I would love to see that! Heres what i think, maybe it can help you form an opinion and make another great video: I personally think that the light bulb would actually light up almost instantly, but not for the reasons described here. I think the cables are indeed what carries the energy, that transformers work by the magnetic field made by the primary side inducing current in the secondary, and that the reason the light bulb light up nearly instantly being that the charge in the wire builds up very quickly despite the wire being so long (this is assuming charge is conveyed instantly when there is no resistance, otherwise i would think that the bulb would light up after half a second). The wire gets charged, so there's a difference in charge at the light bulb. I believe that electrons do not have potential energy, the density of electrons in the wire is what carries charge, and charge is whats carrying the energy. The telegraph cable actually disproves his take, in my opinion. If it was true, the signal would either never arrive, or it would arrive entirely normally. The reason it was so distorted is that the metal protection layer created a giant capacitor that caused all the distortions and slowness. Also, if the energy was transmitted by electromagnetic waves, the inverse-square-law would apply, which it doesnt. If the electromagnetic waves stay equally strong throughout the circuit, that proves that the wires are what creates them, meaning they are what carries the energy. (I shall update this comment whenever i think of new reasons)
WOW! I'm 80 years old. Started learning electronics in the Army in 1959. We were taught the "Right Hand Rule" in the study of inductors and transformers. Although we knew about the magnetic field around conductors we never applied that knowledge like this. Thank you for teaching an old man a new trick.
Two atoms were walking down the street. One atom says to the other atom "oh crap! I just lost an electron". The second atoms says "are you sure?" The first atom says "yes, I'm positive!!!"
EE here; I think most of this info is technically correct, but potentially misleading in some areas. For one, while it's true that energy is transferred in the space around a conductor, as opposed to through the conductor, the *vast* majority of that transfer is taking place *extremely* close to the conductor (we're talking millimeters, typically), due to both the magnetic and electric field strengths decreasing exponentially with distance from the conductor. So in reality, the energy being transferred actually decreases superexponentially with distance from the conductor. Now, in power lines, the ground is still a concern because it's a very long conductor, carrying very high voltage, at very high currents; it's a somewhat extreme case. Yet, even though the cable is *miles* long, we only need to separate it from the ground by tens of meters to significantly reduce losses over that long distance. Furthermore, the ground is only a problem because power lines are AC. If they were DC, you could lay the cable right on the ground, and you wouldn't get any significant energy loss. Edit: see below, the dropoff is not actually superexponential, but the general idea that energy transfer is greater closer to the conductor is still accurate. For two, the analogy of electron flow being like water through a tube is actually still accurate in the case of the undersea transmission line. The metal rings around the cable cause a change in electrical impedance for that section of the cable. In the case of water in a tube, this would be analogous to having an air bubble trapped in your tube. As a pressure wave travels through the water, it will suddenly hit this air pocket, which is far more compressible than the water (i.e. has a different impedance), which will cause the waveform to distort in precisely the same manner as the electric wave does in the cable. Some energy will pass through the bubble, creating your distorted (attenuated) waveform, and the rest of the energy will actually become a wave reflected back in the other direction. This is precisely what's causing the distortions in the undersea transmission line. There's a bunch of reflected waves bounding back and forth between all the iron rings that stretch and distort the original signal. (for the real electrical nerds, check out "time domain reflectometry", which uses this principle to precisely detect where a fault exists on a power line) Third; yes, energy transfer from the switch to the bulb will occur in 1/c time (by the way, I think you could clarify this by representing it as d/c time, where d is distance from the switch to the bulb. You never really state where the 1 comes from in that equation (at first I thought you were implying it was a constant value, unrelated to this distance)). And yes, you do clarify that it will only be a fraction of the steady state energy. But I think you should stress that this would be an *extremely* small portion of that steady state energy. The initial energy that the bulb receives will only be due to the capacitive and magnetic coupling between the two long portions of the conductor. And in the case of wire separated by 1 meter, both the capacitive and magnetic coupling would be practically zero. This again is due in part to the exponentially decaying electrical and magnetic field strengths with distance from the conductor, as well as the poor electric and magnetic permiativity of the dielectric (air) between the conductors. Fourth; addressing your question about "why is energy transferred during one half cycle, but not returned back to the plant in the other half of the cycle", I think your physical demonstration actually explains that perfectly. No matter which end of the chain you pull, there's something down the line offering resistance to the motion of the chain. Heck, you even get friction between the chain and the tube, which is like resistance in electrical conductors. However, if you attached a sort of clock spring to your wheel (such that the spring always worked to return the wheel to its at-rest position), you would indeed see some energy returned to the power plant (you) on the second half of the cycle. This is analogous to powering a capacitive load with AC.
If the energy is transferred in the space extremely close to the conductor, and he said that electric field needs to extend through the circuit (at 6:15) , does it mean that he's wrong saying that the light bulb will turn on almost instantaneously (at 11:45)?
That's a really complete comment. It touches most of the points that bothered me. Thank you. One frequent things I've been seeing on the comment section was the idea of cutting the wire midway through the experiment. From what I understand, I reckon the electric field will just propagate through the wire until it reaches the cut ends; at which point there will be no current and the magnetic field will drop off and no more power will reach the light bulb, correct?
+1 on the technically correct but very misleading train. Everything he said was true, but it implies something that's not quite right. I'd love to see some calculations showing the current across the bulb vs time for the very long wire case shown in the video. If anyone knows a place where that's been done that'd be great! It feels like a lot of the misunderstandings about this come from the classical simplifying assumptions that are made to make lumped element circuit modeling easier. Things like assuming that there's no wave propagation time. This means that the intuition gained from lumped element circuit modeling can fail us. This certainly gets me. The full time dependent maxwell description of this problem is much harder to reason about. The problem as posed seems like a good application of distributed element modeling The other thing that surprised me was the professors talking about how there isn't energy in the electrons. Now this is also technically true as well, in as much as energy is mostly book keeping, but there's definitely an energy change associated with moving a charge in an electric field. You can turn the electrical potential energy into a kinetic energy of an electron. In an electron beam for example. And I feel like they both know and kinda say this, but the way Derek has presented this seems to imply something a bit different. If misunderstood something then please let me know.
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I'm 66 years old. As a child, we lived near large transmission lines in a rural area of CA. They passed over one of our pastures. We had a small water pump shed near the base of one of the towers. I "helped" my dad bury the power wires to the pump shed, 400 ft. from our barn/shop when he was installing a new pump. My dad used pipe strapping tape to mount some fluorescent tubes inside and outside of the shed. Everynight the lights were always on and I asked him why. He took me out to the shed, and asked me if I felt anyything... I realized that the hairs on my arms felt tingly, and I felt something in my ears. He explained about how such high voltage cables as above "induce" a magnetic field way around the big cables, that's what gives me the feelings, and what makes the tubes glow like they were wired to something. That had to have been 1960 /61- as I had just started 1st grade. He drew some sketches to show how "he thought" it worked. He gave me a basic electricity book and quizzed me every once in awhile. His sketches looked just like your graphics. I guess my dad WAS a lot smarter when I was younger. LOL
Yeah. My dad used to tell me a similar story: he told me that fluorescent tubes were constantly on near a big AM antenna and they used it to illuminate their shed also! Anyway, that's not what Derek told on his video. There is two ways of transmit electrical power: wireless and wired. The light bulb will receive a very tiny little amount of power due to wire coupling (electrically or magnetically coupled). But in this case the power is transmitted in a wired way, not wirelessly. Transmission lines like the one over your heads do irradiate a lot of EM field and can be picked up by items that could work because it uses very little power (compared to the amount transmitted on the lines). But it's wrong to conclude what Derek concluded on his video.
I teach physics at the University of California, San Diego, including this very topic. Within an hour of watching this, I set up the experiment, and got the result. I have photographs of the experimental setup, and of the oscilloscope traces. I discussed the results at length with a physics professor friend, and we agree on the explanation. In fact, the load gets (nearly) the full voltage (almost) immediately; there is no (visible) ramp-up time, nor delay through the long wires (delay < 10 ns). This is fully consistent with transmission line theory that is well established for about a century. Dr. Muller's Veritasium series is great, but in this case, there are several claims that are incorrect, or at least misleading. There are many subtleties, and I cannot do them justice in a comment. I would enjoy talking with Dr. Muller to clear these up. For reference, I have a BS in Electrical Engineering, a PhD in physics, and I am author of "Quirky Quantum Concepts", an upper-division/graduate quantum mechanics text supplement. This is my first TH-cam comment ever. Update: I love the Veritasium series, and I have learned a lot from it. To respond to some replies: I chose the simplest case, which I think illustrates the point that power can reach the load without going the whole length of the "wings." The analysis link below the video covers the more-complicated case. My "wings" are 50' hardware store extension cords. My propagation test confirms that coiling them doesn't matter, as expected. My analysis is fully transient, and the circuit transits to steady-state DC over time. Resistance can safely be approximated as zero, but inductance and capacitance cannot, as expected by theory. My load is 270 ohm, roughly the on-resistance of a 50 W incandescent bulb. The characteristic impedance Z ~53 ohm, which is substantially less than the load; that's what's needed for the simple case of near full response nearly immediately (the load is _not_ matched to Z). In this case, the wing capacitance dominates the behavior. Consolidating my previous reply: Examples of subtleties: Do two electrons repel each other? (a) Most people would say yes, and I agree. But one could argue (b) No, one electron creates an electric field, and that field pushes on the other electron. This is also correct; it's slightly more detailed, and from a somewhat different viewpoint, but (a) is still correct, as well. But (c) In calculating the force of (b), we use only the E-field from one electron, even though we know both produce E-fields. To use the full E-field, we have to compute force with the Maxwell stress tensor; this is also correct. There are multiple correct views one can take. The video's chain analogy is very good, and correct. Separately, a few replies have hit on the most-direct (IMO) explanation: the capacitance in the wires provides an immediate, physically short path for the electricity to reach the load. The path of current changes over time. Your gut might tell you that the capacitance is too small, but a quantitative transient analysis using standard circuit theory matches the experiment. Special Relativity still stands. More subtleties: characteristic impedance, etc. I do similar demonstrations in class, so I happen to have all the equipment and experience ready to go.
So...why do we use wires? Couldn't we do without wires in theory, to transmit energy? Basically it needs nothing in between the switch and the bulb, why does he use the wire if it really worked like he explained in the video...?
I am a lowly aircraft electrical technician and mechanic. But from troubleshooting aircraft systems over the years, a fuzzy picture started to form in my head almost exactly like what you illustrated. And I've used that image to do mental checks in my head against where power is going, and if my diagnostics are correct or I have my test equipment in the wrong place. This video completed the puzzle in my head, and I think a lot of people in the blue collar world who work with electrical systems every day without ever defining the knowledge they've learned from it will appreciate seeing this video.
Yes, most people in practice think about electrics as about hydraulics. Closed system where medium (electrons) runs around and does useful work. Pump = battery, power supply, hose diameter = voltage, pressure = amperage, current, viscosity = resistance, valve = switch, check valve = diode, hydraulic motor = motor, accumulator = capacitor, etc. This way of thinking will allow you to solve vast majority of electrical problems. But the reality is much much more complicated.
I think he's playing games with us rather than teaching for clicks. Electrons move and they generate EMF, they're 2 sides of the same coin and can be looked at from eitherside. Nothing wrong with what he said except it doesn't invalidate the otherside, that part he said about it being purely academic, he knows what he's doing. That's why he's getting more dislikes than usual.
Dear SyTy, I sincerely suggest that in your work you follow the procedures established by the aircraft manufacturer and NOT your feelings and impressions you're getting from youtube videos, even ones of such respected authors like Veritassium. As a pilot, I sincerely hope you do.
@@Commander_ZiN Wait, you're still seeing dislikes? I thought TH-cam got rid of them. I certainly can't see them anymore. I suppose they may be 'phasing' it out? Not sure what the point of that would be, though.
Trained in the military about electricity, using the water hose analogy. pressure=V, Flow=A , hose diameter=wire gauge=R . This answers a lot of questions Thanks.
Of course I find this video now… around 6 months ago I got into a small debate with my electrical engineering professor over a topic very similar to this. Everyone in the class seemed to be on the professors side which I guess makes sense but then the following week our professor walks into class and tells me he thought about what I was asking and had looked into it. He walked up to the board and showed some of the similar stuff you did in this video and proclaimed I had actually been correct and my original question that countered his previous discussion he admitted to the class he was in fact wrong. This was the first time in my life I had such a crystallized idea of what someone that was truly intelligent acted like. He wasn’t upset, frustrated or hurt that his initial statement was wrong because he didn’t care about being right, he cared about the truth. I know it sounds corny to say seeing someone look for confirmation instead of affirmation changed my outlook on life but it really did. Never before had I seen some so openly question their very own view and search for the truth rather than search for what backs up their view or idea. Great video, as always
wanting to know the truth and rethinking you own knowledge, just to find out you've been wrong is a true sign of high intelligence. 👏👏👏 thinking that one is always right, on the other hand, is not
Reminds of when I was in 8th grade I argued with my elective science teacher about bullets firing in space his argument was based on the lack of oxygen and I knew that didnt matter since they can fire under water which doesn't have usable oxygen for combustion. I also liked guns growing up and its simple firearms knowledge that the use of self oxidizing smokeless propellants was a huge leap in their development. He reacted the opposite of your professor when we googled it and I was proven right.
"Power and Logic are not related." (-me) People concerned with logic aren't concerned when they're wrong, but people use _use logic_ to wield power get upset when someone else is right - their power is tied up in being right. (Note: that's the core to mansplaining too - explaining to assert dominance, not to bring equality of knowledge.)
Yes, same for me. It is a new concept for me, so I am so glad about the video but unfortunatelly many questions raised that are not covered by the video...
@@alanwannemaker2518 But what if the information in this presentation is in error? How does that profit an individual to spend a lot of time and mental energy trying to understand something that may not be true. It may be like global warming, all garbage but we still won't quit talking about it.
Because he's lying. He's using misleading editing with the professors to try to make it sound like he's saying something counterintuitive. He's cheating the viewer.
dude i cannot express how thankful i am about this video, i asked multiple teachers as to how AC current carries energy when the net displacement by the electrons are zero, like there are electrons that wont reach our home provided the "wire" is extremely long. and so now that i've watched your video, this greatly aided me in understanding AC current and DC current
That's really not a problem. The net displacement of the teeth of a hand saw is also zero, but it transfers energy the whole time it moves, in both directions, just like electric current. This video is misleading.
I'm an electrician from the UK. This theory can be proven by holding a florescent tube near a power line. It will glow. My family didn't believe me so I showed them. So glad you explained this in a way they understands fully. Thankyou. Very clever.
A total physics noob here, Im sorry if this is a really dumb question: But if a florescent tube can glow because it gets energy from the power line, why dont we get electrocuted just by standing near a power line?
@@shiraishichan3944 I feel its all about distance and what you are wearing. I'm sure if you got close enough with no clothing and a direct line to ground. You may experience ark jumping. Its a very good question 🤔
@@shiraishichan3944 hey EM waves not harm us ( like light not hurt you when it falls / passes through you) here energy is transferred by EM waves from the source to the electrical device which receive and convert to their known energy ( electrical) When you keep a fluorescent bulb near it takes those energy which was carried by em waves Same concept using in a current detector in a wire , we actually detect the em waves around wire which have more intensity near it
but wait.. how can that be possible? what if someone cut the wire at the end and then at the same time you turn it on? does it still turn on instantly, but then "realises" 1 second later that the wire got cut and turns off again? I guess from your perspective, you would be turning it on first, and then from your frame of reference you would PERCEIVE the other person cutting the wire only 1 second later, despite them doing it a second earlier from their frame of reference.. edit: but what about signal reflections? what are they then? what the heck was I dealing with with ADSL ports having the signal reflected back to the first wall socket from the disconnected wire leading to the 2nd wall socket? and why do RAM traces on motherboards suffer from reflection?
You perceiving something a second later does not mean it did not happen a second ago. So if at the time of turning it on it gets cut, its not gonna light up. How would that work for the cutter? He wohld cut it, and then he would perceive that the light would be switched on a second later, so he would perceive it as being turned on a second AFTER his cut. Both are wrong as its not about the observer. Its about the event itself.
I know you predicted pushback, and with good reason, so here it is. I’m not saying this video is wrong, but at best, it’s incomplete. First off, the fields can’t intrinsically be separated from the flow of charges as if the electron drift isn’t significant. For the magnetic fields to permeate free space in the first place, the charges must undergo acceleration to create them, and if you cut off the switch, the fields would collapse without the current. If I turned on a fan next to a piece of paper and the paper flew away, would it be accurate to say that the air alone did the deed? Sure, the energy that moved the paper was transferred to it by the air, but neglecting that the fan moved the air in the first place would be a glaring omission. It’s also essential to remember that the Poynting vector itself is DERIVED from the continuity equation (local conservation of charge), and what it represents is the interplay between the energy transfer among the fields and the movement of the charges that generate them. In other words, fields don’t carry energy on their own without the movement of charge. Also, the vast majority of energy transfer in the fields happens extremely close to the wires, and the graphic that you’ve given of these fields taking such wild departures away from the circuit ignores the infinitesimal magnitude by which this happens. With regards to your experiment, the following should be noted. Yes, there would be some current flow instantly with the closing of the switch, but only because the electric field in the conducting wire has had time to reach equilibrium along its length. If instead of a switch, you connected the wires to the leads of the battery directly, the propagation of the electric field along the circuit would occur at a speed less than that of light in free space. Lastly, I challenge you to explain the energy release from the actual light bulb that doesn’t involve electrons flowing through the filament. Also, I posted the following as a reply further on in this thread, but I'm putting it here because it's important. The power (energy per time) that a circuit puts out is always IV (current times voltage). This relation makes no reference to fields of any sort. Now, it is absolutely true that the electric and magnetic fields carry the energy - the current does not - but when one takes the spatial integration over the Poynting vector, it always reproduces the power law P=IV. The fields carry the energy, but the current generates it. You can change those fields in a million different ways and the circuit will behave the same. For example, wrapping the wires in a grounded sheet of aluminum foil creates shielding, which is how high transmission data cables such as CAT6 or COAX reduce noise and capacitance between wires. You could say that they contain the electric fields within the space of the insulation. You could also coil the wires into an electromagnet. However you reconfigure the fields themselves, the fact is that the overall power dissipation of a circuit depends on the current, not on the field strength, and to trivialize this fact by focusing on how the energy is carried is confusing and misleading. As with my earlier analogy to a fan blowing air, the energy may be carried away by the air, but the amount of that energy depends solely on the power output of the fan. Ultimately this video has some good information, but it is also extremely misleading, and I caution people to take any claims that “they way you understand things is false” with a grain of salt. Usually, there’s more nuance than that, and as something of a cynic myself, I think it’s often a form of clickbait. I encourage interested viewers to look elsewhere for the full picture of electrodynamics in all its beauty.
I second Manuela's question. Apparently, you'd first need a general education in physics and only then would studying electromagnetism make proper sense. What would you recommend?
@@ManuelaNChannel @wii3willRule I'd argue without a fundamental knowledge if calculus and/or differential equations many textbooks on this subject would go over anyone's head. Assuming you have such a background, a text on microwave circuit theory (I prefer Microwave Engineering by Pozar) would help paint a slightly better picture of the EM processes occurring inside of a wire. A book like this would also speak on the applications of such methods in broader sense.
I agree, Derek purposefully took a topic lecturers debate about and gave us just enough fuel to start an internet bonfire and not enough knowledge to put it out. He did this on purpose and we'll need to wait for the next video to find out why. This isn't educational, but an experiment on who fact checks. There's nothing wrong with poynting's therom, but also there's nothing wrong with traditional Electronics Engineering. The only thing wrong is his transfromers and undersea cable explainations and then at the end pretending electrons don't have anything to do with it. His entire electron flow was also missleading, sure it's slow and AC goes back and forth but think of Newton's cradle, one ball makes the ball at the end move without ever the traveling to the end. Transformers excite different electrons on the other side, think of it as it's own generator if you will. The undersea cable had issues with inductance that can be explained traditionally. It's like looking at 2 sides of the one coin, neither side is incorrect they both represent the coin. However if you want to design a ciruit you'll use math that follows the electrons. His video was misleading at best and the dislikes are worse than his usual. 176k likes and 4.3k dislikes and most people probably can't see them. I feel like it's a social experiment or he's just desparate for views. There's plenty of resources online for classical electron flow, not so many resources on poynting's therom, I would of expected far more and I couldn't find a single other resource pointing to electrons not doing the work. Derek has sources but not going to go out and buy those books without a better reason as to why.
I’ve been an electronic technician since the 90’s and I remember one of my electronics instructors explaining this to us and it still blows my mind all these years later. Fascinating video, thank you for posting.
Suppose the bulb in the diagram was at the middle of the top line of the square of wires would the field arrows that were in the diagram still move towards the lightbulb?
I think it is a bit easier to picture when thinking about microwave Radio Frequency (RF): they literally have wave-guides that look like steel pipes. From the shapes of these "pipes", it is clear that all the energy is in the empty space inside the "pipe" rather than in the conductor on the surface.
I am not convinced. I think the E field needs to propagate along the wire to have enough intensity to light up the bulb. Otherwise, if I disconnect the bulb from the wire, according to the video, it seems the light would still be on, which cannot be right. Would you might help me understand this?
I think the best part of this video isn't just the information it presents, but also the conversation it sparks in the comments! People asking questions, people trying to understand what's being said, and even people providing counter-arguments in certain scenarios where what Derek explains doesn't seem to match up. I think having civil discussions helps a ton, thanks Derek + the Veritasium community! This video and the comment section is genuinely interesting to go through
@@markmd9 He is partially correct and partially wrong. There will be some small energy transfer between the bulb and the battery in 1/c but the bulk will happen after more than 1s.
The central issue here is the muddy definition of the bulb being "on". It obscures the fact that there are two separate events in terms of current in this scenario. 1) After 3.3 nanoseconds, the light bulb will experience a very tiny electrical signal. This is true even if you cut the wires, and has more to do with antennae than circuits. (Hell, you might as well say the light bulb will turn on *before* you close the circuit due to the ambient radio signals) 2) After 1 second, the light bulb will experience the full voltage of the battery like it would in a "normal" circuit. The energy does travel along the outside of the wire, but the vast majority of it stays very close to the surface of the wire. Thus, when talking about energy propagating in circuits in any real sense, it does need to travel the entire length of the wire.
So if the only switch is at the wire extremity (half a light second away) and is open, then the capacitors are charged and in steady state => light is off When I close the switch (half a light second away) then the light will take half a second to turn « on » right?
Yep! The visuals in the video even show this. While a small signal magnitude will cross directly, most of the flux vectors do actually have a length close to that of the wire. Hence why none of the Profs at the end wanted to guess what would happen in a real experiment because none could guess the "on" conditions
@@christiansimon399 you're going to get a signal quicker than that. Think what the OP said about antenna. It's a direct path. In terms of the "full" voltage, then yes, it will take longer
@@christiansimon399 Interesting question. I don't know exactly how the wires would behave in terms of the antenna effect in this example, but we can neatly step around that detail! In your example, the switch is half a light second from the bulb. So due to relativity, any effect of you closing the switch *must* take (at least) half a second to reach the bulb. So to the extent there is still an antenna effect, it will take half a second to reach the bulb. Which is about the same time it will take the full voltage to reach the bulb.
The part about AC was mindblowing. The Poynting vector is S = E x B but if both E and B are reversed, then S = (-E) x (-B) so the energy flow stays the same!
The visualation was the only why I would have understood that concept. Seeing the diagram, I immediately recognized it as just rotating the circuit along the axis. People who can look at numbers and gleen the same information are wizards as far as I'm concerned.
Still having one doubt: I understand that energy doesn't need to travel through the whole circuit, but how does the light bulb know it's a closed circuit when you flip the switch? Let's say the wire is cut off somewhere very far away from the switch and the light bulb, information should still take time to travel instead of instantaneous. Unless it will work even if it's not a closed circuit, but this doesn't make sense either. It's like I can just flip a switch near a light bulb and it will magically work without a closed circuit. I know it may work without a closed circuit like a transformer, but this setup is not like that at all. Also, mentioned by Rick K in the comments: If this is true, then why don't we use that effect for "faster than light" data transfer? If the light bulb "reacts" to the switch almost instantly, that would mean that the "information" transferred with the flip of the switch is also transmitted instantly.
The information still dont travel faster than light. it just takes a more direct way. We basically already transmit information this way with radio waves. I am still corious about the explanaition of the first part of your question tough...i dont grasp that either
This channel is impressive. You are an amazing teacher and have put together an outstanding video. Nothing about this video feels cheap and generic. Thank you for the authenticity that you bring. I really got something out of this!
Honestly, the analysis from the professors made a lot more sense to me than the video just from a small clarification that I didn't catch from this with one watch, and had left me very confused. The energy most are generally used to seeing from a long, wired connection is from the "transmission line" current, but the energy being talked about here is from "antenna current," and the two modes of transfer, along with major differences in voltage that actually reaches the bulb by either type, felt like important info to leave out. The implication I got from the original video was that the length of the conductor did not matter at all for this model, but the reality was just that the 1m distance in the math, and specification of "any" current, hid the conflicting nature of two modes. So, from my corrected understanding: The "transmission line" current *would* take one second to reach the bulb, through electron to electron EM field interactions in the wire, it's just that the "antenna" current can travel there first, because of a lack of shielding, and the misconception/lie here isn't so much a misconception/lie, but a lack of information on additional modes of energy transfer. It felt like this video was more focused on becoming a popular, trick question via omitting information, rather than informing people on new or misleading information, which is not something I would/could say about any other Veritasium videos I can recall, and I do not like to say.
Agreed entirely. This felt more like a parlor trick gotcha rather than any deep (causality-violating) explanation of a fundamental misunderstanding around electricity
Reviewing the comments, I see that many others share the misinterpretation that I had, and I feel that is not a good reflection on the clarity of this video, with many accepting that interpretation as fact even in the case of others pointing out causality issues. If I am wrong, I will accept that, but this is my current opinion upon what I have seen as of now.
well I mean the question asked was how long till the bulb lit up. It doesn't matter about how long the current takes or anything else. just the bulb. I think you just didnt listen to the first words of the video.
I guess the next question would be what's the ratio of antenna to transmission line current in standard environments, how significant are the two sources.
man, I'm generally a fan of yours, but I do hope for an errata on this one. You're absolutely right regarding the fact that the energy is propagated by the fields, and not the wire. But your explanation (and specially the answer to the '1c*s wire question') hides the importance of the wire: IT GUIDES THE WAVES. Without a wire to guide the waves, you can't propagate the energy at all. Meaning: the state of the wire is important. If the wire gets cut, the energy won't be propagated, as common experience shows. So with the long wire situation, the fields will take time to propagate based on the length of the wire. Not because the energy is propagated by the electrons, but the wire is what guides the waves from the source (battery) to the load (lamp). Think about it: if the energy arrived 1/c seconds later, what's the point of the wire? Of course there are secondary effects (through capacitance, inductance and radiative effects), but these mostly die out at a time scale much shorter than 1 second, and are much, MUCH, less capable of transmitting energy than the conductance effect which is capable with the wire. You mentioned this briefly, but your brief explanation (and the graphs you show) implied that you were talking about transients (since you said it depended on the impedance), but transients also only travel at the speed of light.
The light turns on at 1/C? If that were true wouldn't you be able to setup two circuits and communicate between the two ends faster than C? Seems to break a few theories...
As a tradesperson who has created and installed many home wiring circuits, wired up car stereos, installed lights and even built circuit boards; you have shattered the sense of pride and accomplishment in what I've done by pointing out I didn't REALLY know what I was doing. I'm going out to rub two sticks together in order to claw back some small semblence of human ingenuity.
To be fair, this is very misrepresented in this video and arguably incorrect even though everything stated is actually true. Ultimately the power is inducted into the light as the em field generated around the battery and outgoing wires propogates outwards at C. IE: its basically the same type of inductance you see in an air gapped transformer where current and voltage are generated in the light by the inductance of the power from the battery after 1/c seconds. So yeah technically it is "on" (sort of at an extremely minimal state though it would not be visibly on). With what we classically think of as "turning on" occuring at 1sec once the electric current also travelling at c (along the longer path) reached the light through the conductor.
Don't feel to badly. All this desktop research about power transmission is really interesting but how many of "them" have wired the same number of houses successfully as you have?. Still I am grateful for the knowledge shared here.
I got the same rude awakening but once I accepted it I feel much more excited about the possibility of free energy from tapping the earths natural magnetic force and static electricity. I believe Tesla’s experiments in this field we’re grossly underestimated ...or purposely sabotaged. All we need to learn now is how to throw the “on” switch to power our homes, cars, airplanes etc. We already know we can run cars trucks and airplanes on electric motors. All we need is to find the vector of the flow to find where to put the “on” switch.
@@Peter-gq8uh I agree. I’ve watched electricians wiring new homes and how fast they move through the room. The wire literally seems to become molten and flow into the switches and through the metal boxes into they’re receptacles. They become so fast you hardly see the insulation flying off the ends of the wire and they’re already connected to they’re receptacles. Understanding the mechanics and engineering of something perfectly and making it work does not involve the science of electro-magnetic flow and chemistry, physics and other scientific facts. And thank goodness for that or we’d still be living in potato huts.
Speaking as an electrical engineer, electricity is the closest thing in to magic that everyday people deal with. I deal with conceptualizing electricity and electrical components every day, and you're kind of forced to think of amperes like your chain analogy, voltage like water pressure, transformers like gear boxes, etc. But you have to keep in the back of your mind the whole time "but it's not water mains or a gearbox, it's electricity". It's simple up close but a whole other different thing when you try to think of the whole power grid at once. My advice to laypeople? Learn what you can, and marvel at the physics of electricity with me! ...But call a professional if you need to wire a car charger into your garage.
@@nathan87 electrician here; we’re not labourers or handymen, we’re trained in electrical theory and hold technical qualifications. We may end up slightly dirty at the end of a work day but we’re well paid and quite knowledgable 😊
I am exactly the kind of person the wise man was referring to when he said "A little knowledge is a dangerous thing". I'm exactly the kind of person who would learn the basics and immediately think they could DIY their own car charger, lol. This video, and indeed this comment, are good reminders that I don't know ANYTHING about how electricity works, no matter how many cool analogies I know.
@@nathan87 But he will certainly be aware of the dangers evolved with working with electricity! As the OP already quoted, electricity comes pretty close to magic: you can't hear/smell/see it, but it can kill you quite easily.
My grandmother lived on a very remote and isolated island in Norway. When they first got electricity, they had one lightbulb connection hanging from the ceiling in the best living-room (it was only used when having fine visitors). The thing was that when the electrician first lay out the cables, they had no bulb to put in the socket. Also the electricity was not yet connected to the house but would be soon. So each night they put a bucket under the empty socket just in case the electricity would be connected while they was sleeping. Not to spill anything on the floor.
A colleague's grandparents, living on farm land in Belgium, would dress up on Sunday to watch television, thinking the presentator was actually talking to them and did see them.
I have a friend who turns off the switches on all his unused power points - not because of safety, even though that's sensible - but because he believes electricity pours out when there's nothing plugged in, wasting his money.
Derek is somewhat right about the time being roughly 1m/c for the bulb to light up but only because the parameters of the problem were picked to be tricky (sometimes fun and educative). Unfortunately Derek doesn't go into details in the video and only says that the bulb "won't receive the entire voltage of the battery immediately". This may mislead you into thinking that the signal speed in an electric circuit depends not on the length of wires but on the air distance to the switch, which is wrong. The signal speed in wires is roughly 50-95% of the speed of light and most often is what dictates how long it takes for something to turn on in most circuits. This is why, for example, matching copper trace lengths in PCBs is often important. Or why high frequency trading companies care about their internet cable lengths. HOWEVER, often in circuits there's significant wireless EM radiation, intentional (radio, wifi, microwave) or unintentional (reduced with EM shielding). Turns out that in Derek's circuit one side of the wire initially acts roughly like an antenna while the other acts like a receiver and the power transmitted could be enough to light up an LED bulb. At 100m it wouldn't.
I share this sentiment. The EM influence at 1 meter takes 1/c seconds. But unless one has a clever inductive power transfer, not likely to light up the bulb. I tried to do the experiment today in the lab with 30 m of wire to make a video but the problem in the real world is dealing with inductance of long wires---but that said, I could kinda measure a 200 ns delay so at 100 ft, 50% the speed of c, that delay is right on par with what one would expect if the power has to traverse the length of the wire. A wire has the ability to contain the EM fields along the wire path and thus transfer power efficiently. However, with all this talk of wireless charging and some MIT breakthroughs, I can see this as a segue to that topic.
I am a third year Physics uni student and I can onfindently say that you have managed to explain the poynting vector better than any of my professors ever have...
Isn't that the truth. And also after working in the field for many years. I learned so much more on the job. Hardly anything I learned in school whatsoever.. barely. Just the basics.
Bro you need to watch some Eric Dollard lectures... I would recommend "History and Theory of Electricity" and "Origins of Energy Synthesis" right here on TH-cam if you really want to get at understanding the essence of electrical phenomena. Just remember that a Theory of Everything has grave implications for Aerospace and Weapons development, and thus has major national security implications should it ever be out there for all the world to see, and thus why for the most part, we are kept in the dark as a member of the general public on topics that get deep into the essence of the reality of nature and natural philosophy!
This was a GREAT explanation of circuits and electromagnetic energy. The one thing that could be talked about is that if any arbitrarily small current can turn on the bulb, then the long wires used to completed the circuit are not actually necessary--you could just use an antenna--and in this light the explanation is already common knowledge. It would have helped to emphasize the role conductors in "shaping" the fields, and that they are absolutely necessary to deliver enough power to the bulb, which would not be receiving maximum power until the signal travelled all the way down the wire.
I was thinking exactly this. The way he was describing it made it seem like the wires weren't necessary. That you could just "shoot a field" at the lightbulb. I honestly still don't quite understand what the actual process is.
An antenna does not supply current to disturb the electromagnetic field. An antenna receives light waves, and processed into a signal using current supplied to what ever appliance. A Tesla coil however, can produce high enough voltage, that it disturbs the electromagnetic field very well and can excite the fields even in very insulative air, to power devices in it’s proximity. Watch videos on people powering light bulbs (and many other things) from the air around a Tesla coil. This might be the “antenna” you were thinking of.
There is so much to electromagnetic Fields and the like to explain, that this video could not explain it perfectly as well. The Experiment is kinda obfuscating the whole thing. A Lightbulb is commonly known to take a while to light up and to draw a bunch of current. A small LED or something like that would have made that topic better understandable. If you were to do that experiment in real Life, with a real Lightbulb, then you could certainly see the time it would take for the bulb to light up. With a low power LED you would certainly not see the time it would take. Both having conductors with 0 resistance, but otherwise normal electric behaviour.
I have so many questions: - If the energy moves through the fields, how does it light a bulb? What takes on the energy? - People in the comments talk about shielding the bulb from EM fields. How does it work then? I need pictures. - how do computers work, transistors, if it's not the current that moves the energy? Give us more of this!
For the first question, the energy, after traveling through the electrical and magnetic fields from the circuit, will reach the bulb which has its own magnetic field around it. The energy will travel through that field and pass through the filament, thus lighting the bulb
The point being made is that the long wires back and forth will function like an antenna, and so the switching on will create a wave that is propagated over the distance between the antennas. The bulb will sense this (arguably quite weak) wave and flicker on. As an engineer I find this experiment a little frivolous, I think it will confuse people more than it educates people
@@jemert96 Exactly. You can see it as a two transmission lines or antenna. And it's unrealisitic long wires. I find the presentation kinda dishonest either way.
@@jemert96 It is also worth mentioning, that let's say two 300km straight wires with 1 m gap that aren't actually connected will for 1 ms (thinking about it, likely 2ms, but not so sure about that) act exactly the same as the 1c long cable. And the "not whole current" after the 1/c will be so minuscule, that nothing will actually happen.
I've always loved watching your videos. Ever since I was a kid, I've always wanted to be an electrician. After watching this super informative video. Im proud and happy to say that I am still not an electrician, and I will never be :)
Another important thing worth clarifying is that prior to the switch being closed, we have to assume that the system is in a steady state with a buildup of opposite charges on either terminal of the switch (if it wasn't in a steady state, then the light would already be on). When the switch is closed, current starts flowing (which sets up the magnetic field and radiates energy as discussed in the video), but it starts flowing at the switch and not at the battery. The battery doesn't "know" that the switch has been closed until the Poynting vectors from the switch reach the battery. So it's really the distance between the switch and the bulb that determines when the bulb first experiences any current, and not the distance between the battery and the bulb.
Yeah this is a huge piece of the puzzle. The "event" in this case is the switch flipping, so for causality purposes it's the switch-to-bulb distance that matters.
Is this true cuz that’s makes so much since. Or is it like what he said in the video the energy is going from the battery to the lightbulb directly through the air? What would be the case if the light bulb was intact 1/2 light year away but the switch stayed close. Alternatively what if the switch was 1/2 light year away?
That makes more sense to me. I figured there would be a buildup of charge at the switch, and that the system could be simplified to electron source -> bulb -> switch -> electron sink, and it didn't matter that the source and the sink were at the same point. Only the fact that the bulb and switch were close together mattered. It led to another thought experiment: what if there were two switches at the battery terminals that turned on simultaneously? To me, it made more sense that the electric field would need to propagate along the path of the cables, and only once it reaches the bulb (halfway) do electrons actually begin to flow along the electric field, creating the magnetic field. There is no Pointing vector without the magnetic field, and thus energy cannot flow until that electric field has fully propagated along the entire 2 light-second path (though it propagates from both ends, so it would take 1 second). EDIT: Then again, what happens when the battery is a light-second away from the switch-bulb combo? Close the switch and the bulb is close, yes, but the battery has to somehow send energy 1 light-second away to the bulb. Would the energy have to travel for that full second? Or is there already energy that's "stored" in the existing, nearly-complete field?
I think one of the most difficult things about the Poynting vector is to visualise the cross product in your mind. That video with all fields represented in space is extremely helpful and should be shown in EM courses.
I see many engineers talking, and as non-engineer, I got more confused Hope you can do a follow-up video! Some questions I hope I can learn more about: 1. The video seems to suggest that to transfer energy, just setting up a simple wire to set up the electrical field is sufficient. So how does resistance, voltage and the entire electrical engineering degree come into the picture? 2. With so many wires around the world, do these energy fields interfere / cancel each other? I might have some misconceptions, so do advise!
1. this video ignores the *amount* of energy transferred in this way. It's true that some amount of energy always takes a straight-line path, but in real circuits, at steady state, almost all the energy is concentrated around the conductors (though still extending outside them to a measurable extent). 2. Yes, technically, every conductor that isn't perfectly shielded (which is of course impossible in reality) is an antenna, and both receives and transmits energy. In practice, we minimize unwanted signal transmission through shielding and just lump everything except the particular signal we care about into "electromagnetic background noise/interference", (which you can hear as literal noise with an AM radio) and try to make sure that the signal we do care about is many times stronger than any we don't care about. It's also possible to do signal processing to filter signals by frequency, making it easier to ignore background noise.
1. Resistance will cause the electric field to turn at a slight angle, opposite of that of electron flow. The energy flow vector will end up having a slightly inward angle, sending some of that energy into the wire (which ends up heating up the wire). 2. Yes, wires do interfere with each other regularly. Interference from wires is one of the major causes of internet connection unreliability for many people. The fields almost never cancel out though, because the electromagnetic field strength weakens rapidly with increasing distance from the wires. By the time you're a meter away, it mostly just introduces noise, rather than anything serious.
Basic answer - Electromagnetic energy propagates outward, in all directions, from the battery and the wires. Electromagnetic energy also travels infinitely far, but at insanely-reduced energy, as the energy inversely related to distance. So yes, all of the wires in the world do technically interfere with each other, but because of shielding and their distances apart, the interference is completely negligible. And yes, you could use just wires with no closed loop, but the energy would only be a short burst when you flip the switch. And don't forget, this entire concept is also based on zero resistance in the wire. In the real world, you would never have enough current to even "see" the bulb light up. You would need insanely high voltage to pass it through 300,000,000km of wire.
@casper . Isn't it crazy our whole life is based on things literally like magic and we act like its normal? Oh so this cable transfers energy - whatever it just works. Oh this LAN cabel transfers literally billions of bits every second? Okay nice it works. I even learned how the LAN cable looks inside but it doesn't help - it's still basically magic but as long as it works. Only one human has to understand tech to bring it to 8 billion people.
2 questions: 1) Why does the light bulb have to be connected still? If I put a second bulb near the first one without connecting it to the circuit, why doesn't it also "catch" some of the energy and light up? (In particular in AC so the electrons already inside the bulb can be "reused") 2) What happens if a second bulb is added suddenly to an edge of the long circuit?
If I understood it correctly, for the energy transfer to happen you need both electric field and magnetic field, when you connect the wires, the electric charge propagates and you've got electric field then because of that the electrons start moving and you've got magnetic field. I would say "the energy uses both fields to travel"
@@SukSukulent You would be correct in assuming so. Also, air by itself isn't an incredibly efficient conductor. But the principle works, since we now have wireless charging stations, where you don't have to connect your phone or devices to a cable for them to charge. If electricity had moved through wires like most people think, that wouldn't be possible
1) You are correct, in the instant the switch is flipped, the bulb will receive some energy regardless of whether it is connected or not. 2) It will turn on some time later, when the propagating fields reach it
This is an issue I really need to think about, I'm a very good, now retired mechanical/electrical diagnostic & repair technician but I just accepted "electrons vibrate power flows in line" explanation and went to work. I've a always wanted to get back to this eventually. It's been 50yrs and eventually is here. Thanks for your great explanation, it's fantastic and very thought provoking!
Yeah, I'm a low level tech but do high end electronics including power conditioners. My first reaction was to wonder if Ohm's Law is valid, assuming this is. I can't agree or disagree. Interesting, to say the least.
@@rickmilam413 Great point, I didn't even think about Ohm's law but I can still see how it applies. The atoms and electrons still move, vibrate and get stretched a small amount while remaining in their overall place and they vibrate faster with increased voltage pressure, so the resistance would increase. That makes sense to me anyway!
I was taught electron flow theory. Each electron jumping to "hole" along an infintessimal string. That was 30 years ago. Existence of proton and electron along a timeline. So neutrons seem to attract all particles. I wish I still had a copy of Francis Bitters book. "Magnets" the education of a Physicist. Works in progress to study celestial objects and their flux lines. I can barely scratch build a low power am/medium wave radio, So I am no authority on electrical theory. Earth has an iron core. So I maybe incorrect in opinion that electrons always seek the easiest path to earth ground. Free electrons being confined in the earths magnetic lines of flux. Lightning discharging in reaction to corona activity of our sun. Lightning is emitting somewhere on earth as manifeststion of lines of flux altering as our planet continues orbit around Sol. Tesla chose Colorado for his wireless transmission station with a purpose in mind. Presence of conductive minerals underground. Ribbons of ores act as wires for electrical conduction. Some minerals being more conductive than others. 400 years of ore extraction by man has altered the static flow of seismic conductivity. Tons of materials moved from below the earth to the surface. Changing the flow of electrons. Seismic disturbances ebb and flow and continue altering electron flow until Unity lines of flux are restored. Polar flip is merely a tip of electron alignment of earths magnetic poles. Mineral fluidity under heat and pressure affect the magnetic lines of flux. Tesla could not finish his work to build another transmission tower south of the equator to prove his theory.
@@jasonb4703 The electrons don't actually leave the atom they are attached to, think of it like knocking over a domino in a line of domino's. You 'add energy to it by tapping it' so it falls over and bumps the one next to it transferring the extra energy, to the next to the next to the next and so on down the line but each domino remains in place. They don't actually travel from place to place along the wire or circuit!
This video is misleading. Just because the Poynting vector points in the direction of energy flow, it doesn't mean that it causes the energy flow. The conclusion is also dead wrong. Anyone working in a lab with a fast scope can observe the time it takes for a signal to flow down a wire. You don't need a stupid impossible single wire 2 light seconds long. All you need is a few feet of wire on a bench, and a signal generator with a fast pulse generator. Sync the scope from the generator, and probe along the wire. you will see that the pulse is delayed a bit more than 1 nano second per foot. Putting the end of the wire next to the signal generator doesn't make the time delay go towards zero. By the way, for fast signals, the wire should be a transmission line, that consists of another return line spaced closely to the signal line, that is grounded. It could be a twin pair, or a twisted pair, or a coax with carefully crafted test points. The load should be a resistance equal to the characteristic impedance of the transmission line. Otherwise, you get the signal bouncing from the end of the line and traveling back to the generator.
At the end of a very intese physics course and right after the exams, our teacher ended it by telling us that everything we had just learned about the flow of energy in an electric system was most likely wrong and mentioned something about energy not passing through the cables. Now I finally know what he meant. Thank you 😅🙇
@@rocketpig1914 I might be wrong, but I think they are essentially allowing the magnetic field to form properly in the loop configuration and essentially becomes the structure the fields will form around. So for example, without the cable, you can't turn on a battery or switch and just power your devices, it needs a bridge to stabilize around and focus it's energy into. But maybe I am flat wrong, but this is how I am kinda understanding it
I do remember thinking it was weird that a ring voltometer could work at all, If the coating of wires was a good enough insulator to protect me, why would a voltometer work at all? I won't pretend I've fully grasped the info in this video, but it does help me realize the importance of the field itself.
I worked with electronics successfully for years, and am severly confused now. I guess a working model is different from an actual model. I do want to see it accurately, because I'm of the opinion that you can do the best work and achieve the most that way. I'll keep reading and watching until I understand it I suppose.
He talked about electromagnetic energy, electrical energy still flows through the wire, but you can still use the poynting vector there to see the flow of energy because the current in the wires generate magnetic fields.
I've said it many times and I said it now. I'm a nuclear engineer, and the functioning of a nuclear reactor is pretty clear and understandable for me ... Now, how does the electricity generated arrives to your home : MAGIC. It cannot be otherwise
I second that motion. I have a mechanical engineering degree. Why do they have to obfuscate the truth with wrong answers??? First they tell you electrons aren't really going in this direction, they actually move in the opposite direction. Then they say PSYCH the electrons aren't really flowing at all! Then they do some hand wavy right hand rule black magic and boom, electricty.
I have a question: Let's say the far end of that 300,000km wire was cut, then the light bulb wouldn't turn on, so in 1/c seconds I would learn that a cable that is half a light second away from me is cut. Doesn't this violate the idea that information can only travel at the speed of light?
I'd assume that the segment of the wire that you're observing still has a charge, but Idk anything. Really I'm just commenting to get notified when someone who actually knows answers your question
Holy crap. I have degrees in engineering, have investigated numerous electrical fires and worked for decades developing electro-mechanical devices, and no Electrical Engineer has ever explained electricity this way. Things now make a lot more sense.
@@variamente6855 The question is asked in highly misleading manner. There's no "misconception", Maxwell equations are known and taught in 2nd semester of engineering degree.
@@leonidfro8302just because they're taught clearly doesn't mean their implications are understood. As you're evidence of. Most people in these comments have studied engineering, as have I. Over a decade ago.
I’ve watched this video all the way through multiple times and even though I’m paying attention each time I am going to end up watching this again multiple times and still may never learn anything but each time I feel at least a little smarter🎉
What he ment to say is that what 99% of the population was taught about electricity is wrong. I found myself saying; "that is very interesting. My knowledge of power plants and electrical fields generated within power plants leads me to believe that this is more likely true and I wouldn't disagree with the conclusion."
Everyone's stuck on information traveling faster than the speed of light, but it doesn't.. It's traveling 1 meter in 1/c seconds. It just doesn't take the path we've always been taught in primary school..
Hello Derek, a physics professor here. I love your videos and I subscribe to your channel - in all honestly, I consider it the best example of public communication of physics and science I have ever met - I am not exaggerating. I actually used some of your videos when teaching to my students. However, you did not convince me with this one - not that I love you any less for this. I have similar objections to some that have been made by others here. The explanations of the fields, and the Poynting vector are gorgeous and very instructive, by the way. But I have tried to explicitly calculate the flux of the Poynting vector on the bulb, and I find it to be quantitatively a small effect (quickly dropping with distance of the bulb). Yes, there is *some* disturbance at the bulb, but I think it is a bit misleading to just say that it "turns on". I suggest to have this checked by other people - I would be very curious to see a follow-up on this. You are actually tempting me to try this out in my own lab. Anyway, even if it turned out you had slipped on this one, that does not change my opinion about your work. Physics is non-trivial, and what really matters is to have the right scientific approach to problems, not to never ever make a mistake (even Galileo did) - eventually things sort themselves out if you follow the right track.
I agree that physics is non-trivial and that anybody can make a mistake. But I'm a little disappointed by the lack of experiment. The thought experiment is a good idea, but a real experiment can show that you are right or wrong, and that is extremely important in the scientific method.
PS: to be clear, the reason for the effect not being immediately "complete" is that, although the energy does propagate through the fields and not the wires, the fields do not reach their final configuration until the other wire also settles in the final configuration, that happens only after several back-and-forth along the long wires. One variant to this problem is move the switch to the other wire, next to the light bulb - what do you think would happen in that case ?
Yes I also think Derek has made a misconception. When the DC current flow is stationary many seconds after switch is closed, then the magnetic fields of the long folded wires cancel themselves out because of the symmetric current. There is no statc field either on the outer wires since they are on the same voltage potential and the resistance is defined 0. So In the end there is a resulting energy flow actually over the short distance battery to bulb. So far so good. But as long as we have a switching event, the fields need to establish, and this takes time with the speed of light. When switching on, the voltage potential change on the wire end triggers a wave traveling along for one second until it reaches the bulb. However I am wondering if this argumentation can still be done while assuming the impedance, thus capacitance and inductance of the wires to be 0. I feel this is contradicting and at least a non-zero inductance is needed.
As an electrician, a very curious one who always has to dig deeper into the why and hows of life. Im aware of the concept. Ive never met another electrician that understands or believed me. Great video.
Well, not to say that you’re wrong, but I too have thought this and I’ve been an electrician (now retired!) that thought I was the only one of us to believe it. Where’s Nikola Tesla when we need him???
@@WyrGuy2 i didn’t say they didn’t exist, i just stated i hadn’t met any of them. Now i can say that i have. Nice to meet you. Tesla was a crackpot… an absolutely brilliant mind that i feel had more discoveries left to share with the world.
As an Electric Engieneer(since a year or so), it seems my university never bothered to update on these topics, i learned about electric and magnetic fields as separate topics, and in some of the first and more basic courses about electrons moving throught the surface of cables. So its nice to see a video going deeper on this. Oh and just a little comment, electricity doesnt move at the speed of light on a cable, its better to call it "at the speed of electromagnetic waves throught a medium", and that material will affect to some degree the speed of propagation. Edit: or wait, is this tied to the incorrect explanation? since the fields travel through the air instead?
I am a Master Electrician for 30 years and we more or less where taught power was sent the tough the "skin" of a wire. Fact is many terms used are made simple so people can grasp it in real life situations. Wires clearly have a magnetic field around them or am amp probe would not work. Also working with high voltage cable there are bleeders around the cable like coax cable to discharge stray voltage or with cable wire shield it from stray voltage. I have a collection of old electrical code and theory books back to 1897 that hint at forces they did not really understand but they were spot on in almost all theory even in 1897. The books were made simple to explain wires like plumbing pipes, size vs pressure and this was good enough to have a practical understanding to size wires correct. I see this a lot like gravity when it is calculated as a force that pulls or attracts mass. That is not how it works but the math is correct even if the understanding is dead wrong. Mass bends the grid of space so objects are traveling straight on the grid but the grid is distorted.
Poynting derived his stuff in 1884. But it is largely irrelevant for circuit theory or even for transmission line theory on which the bulk of even very advanced electrical and electronic engineering is based. This video does not portray this truthfully.
I loved this video, and I agree, when it comes to educating people for practical real life scenarios, sometimes it makes more sense to give approximations that work well practically. But I guess the crazy part is that the teach it that way too even theoretically.
The video is theoretically not incorrect, but very misleading and I think a bit sensationalized to draw likes. Thank God physics professors don't wire up our homes!
I'm an electrician; not the sort that you call for installation or problems at your home, but the sort that does industry support (automation, controls, low voltage service, etc). I love the conversations that arise when someone comes around with seemingly random knowledge that is applicable to our work in ways not often considered. Without fail, everyone starts off with the, "mmhmm, sure buddy" look. Then something clicks and suddenly they realize that voltage output in our 3 phase motor drives is proportional to frequency. Cranking that output up to 100Hz to get more speed causing failures is starting to make sense. Then everyone is full of questions. A group of middle to late aged blue collar folks clustered together in a dozen different excited discussions. It's a beautiful thing, that I'd wager isn't often witnessed outside of enthusiastic classrooms. Easily among my favorite experiences. I bet this one will lead to something interesting next time we find a disconnected shield in some com cable.
I'm an electrical engineer too and I can't agree with the video because of the 100m ethernet cable limit. If you need to route ethernet to a terminal across a factory floor, you might be forced to loop the cable into the ceiling ducts due to safety regulations of obstructions. If the ethernet cable length exceeds 100m, even if the terminal is merely meters away on the other side of a wall, you are out of luck. However, if Vertisium's conclusion that the bulb lights in 1/c holds, then delay is limited by Euclidean distance and not cable length, and I'd be able to make the connection even if I used extremely long cables. This is clearly not the case.
Meanwhile we once had a new young electrician asked to connect some wires to be used for some angle grinders. The bosch exploded, then the dewalt. The kid sent 3 phase current instead of taking just one phase and ground as neutral (probably not code but it works in a pinch, im not an electrician btw)
At last!! I had a high school teacher 54 years ago (Dr. Schoenfeld) that beat your electrical pressure/EM field transfer of 'electricity' through a circuit in our heads. Later, I recall on a test in college Physics 110 where the correct (or accepted) answer was always ' ...by virtue of the flow of electrons through a conductor'. I always wondered how many of us students took a fraction of a loss in our GPA due to this belief. Excellent video explaining how capacitance (or inductance) play a role in something most everyone takes for granted. More I²R to you!
I'm still not sold on this idea. The Poynting vector is a just a representation, and not meant to be taken literally. It's like velocity. Velocity has a vector that can take several small components and make a larger vector using vector algebra. Same with the Poynting. The power transfers by several small jumps that contribute to the overall sum vector. The case of the undersea cable doesn't prove anything about power transfer as a whole vector- it only proves that electric fields transfer better with an insulator as in coaxial lines.
I just want to point out that in your setup, (battery, wires, switch, lightbulb) there can be no impedance, because your power source is direct current, not alternating current. (I know small irrelevant detail. It matters to me, because as a newly licensed HAM, I've been studying RF quite a bit lately.)
I have studied electrical engineering for four years. I finally understood why we as an engineer sometimes needs to approach a problem in scientist way. We are just applying some formulas without digging deeper to the profound concept of understanding.
Yeah the electronics engineering courses I took gave Maxwell's equations the same cursory treatment. It annoyed me so much that we only covered the 4 commonly cited ones while there are actually more to his work.
There are aggregates of inprinted sheets of papers glued together we call "books", you can purchase this kind of stuff or borrow them in various places on this planet. generally they come in different sizes and contain informations on the subject of your choice. you will be surprised, if you read some early electric motor sheet paper aggreagate, to find out that there was not a single innovation in this domain in 100 years, and all of the discoveries on this topic were made by one dude named N̶i̶k̶o̶l̶a̶ ̶T̶e̶s̶l̶a̶ Elon Musk.
In electrical engineering, power system for long transmission line, voltage and current are assumed to be traveling as an electromagnetic wave, but never knew time for transmission depending upon the vector displacement between source and load.
A fraction of the energy passes through the fields directly between the source and load, and another (larger) fraction passes through the fields near the wire. So in the idealized case discussed in the video, a small amount of energy passes through the air, and that's enough to light the bulb. For most realistic circuits with relatively short and widely spaced conductors, the amount of energy passing through regions of space distant from the wire is pretty much negligible, particularly since most realistic systems have a minimum voltage/current at which they'll activate. The answer in the video is only correct under the assumption that ANY non-zero current is sufficient to light the bulb. If the bulb in the video required a minimum voltage across it that was some fraction of the battery voltage, then it wouldn't light until a sufficient fraction of the energy from the battery arrived at the bulb. Most of the energy travels very close to the wire, but there are also paths directly from battery to lightbulb, as well as paths that follow near the wire partway and come back near the returning wire. So the voltage seen by the bulb will gradually increase as energy along each of these paths reaches the bulb, with the full voltage only showing up when the fields travelling very near the surface of the wire arrive (~1 second in the setup in the video where the wires are one light-second long from source to bulb).
So you are saying that if I took a magnifying glass and drew dense field lines very very close to the wire most of the energy travels through that all the way?
Yes, exactly! Veritasium essentially just showed as that a nano-Watt of power will radiate instantaneously as if the light bulb is the receiving antenna of a radio. Totally not what his question was framed as asking!
I completely agree with you, I feel like the question is misleading and the "correct" answer is only valid for a very small distance between the source and bulb. The wires still serve a waveguiding function and the vast majority of the energy propagates along them.
With such a long wire, how do the fields "know" where to go? How is it able to transmit energy immediately, but a disconnected lightbulb another meter away wouldn't power on? (or maybe it would?) In fact, how does current "know" to start flowing when the circuit is complete? Or what would happen if you cut the wire at one of the tips? Would the field instantly start receeding everywhere? 1/c seconds to turn off?
If you want a more detailed simulation see the video I posted after he posed the question the other day. I can simulate your alternate scenario as well if you'd like!
This has been amazingly helpful. I cannot learn the way my education teaches. I know they try to simplify things down for children to understand, but if I can't clearly picture how something works it doesn't stick in my brain. I need the greater depth for it to make sense. The information they taught in school always contradicted what I learned outside, and that lead to endless confusion. Electricity therefore became a point of endless procrastination because I was just so damn frustrated with it.
Like a lot of comments on here, there is a big problem I saw: You’re severely undermining the importance of the cable. Yes, the magnetic field carried the energy for the bulb to light up. But the field is strongest right at the wiring. The instantaneous power going to the bulb is a very small fraction of the field. The wire acts not only as the way for electrons to flow, but also for low impedance transmission. The transmission through air is much, much smaller than transmission following the wire. EDIT: Veritasium's new video clears up the major hole that this video brought up. His visual representation of the circuit in the original video was the major issue. The point I made still stands with that representation (insulated cables, car battery, lightbulb). I'm glad he refined this.
That is exactly what I thought after watching the video. The power transmitted through the EM field has the highest flux inside the wire due to metal's high permeability. If the power could as easily travel through air as through metal, we wouldn't use wires to transmit energy/signal in the first place.This is correct that the light bulb in the experiment would light up after 1/c s, but it would be initially very dim, and gradually increasing in brightness until after 1s, when the EM fields traveling through the wires catch up.
@@mateusz7590 Uhm...he did say exactly the same thing in the video, tho. I think people are just pointing out at simplifications made for divulgative purposes.
These "thought experiments" are never meant to be broken down, otherwise you will always find mistakes. They are obviously wrong, that's the whole point, otherwise we can continue adding an arbitrary number of real considerations and debate whether my personal choice of considerations are more accurate than yours. In reality none are, they are just meant to more easily represent a specific phenomenon, such as the fact that energy can in fact travel through air, which was the point of this video.
@@mateusz7590 Yes, there will not be enough energy transferred to the bulb until the waves have traveled sufficient distance down the wires to induce enough current at the bulb--even over one meter there is going to be quite a drop in power. He seems to imply that the energy jumps from the battery to the bulb with sufficient power to light the bulb--answer was D.
This is basically transmission line theory (I'm an electrical engineer who specializes in this, in electro-magnetics). You can view the two lines connected to the battery as a dipole antenna, same for the lines connected to the lamp, and that the two antenna's are shorted at the ends to one another. These antenna's operate in near-field. Another way of looking at it in this particular case is that a capacitor is formed between the lines connected to the battery and the ones connected to the light-bulb. I do not agree however, that the circuit behaves as you said it would, the power transferred should be in the order of milli- or micro watts which is not large enough to cause the lightbulb to glow visibly as it would require tens of watts, you should put it into an electromagnetic simulator to calculate the exact power transfer.
The "light bulb" is really an idealized current detector which consumes no energy from the system. Thus, even if just a nanowatt is transmitted to it, the "light bulb" comes on instantaneously at detectable brightness. Obviously real electric light sources do not behave this way, but this is a thought experiment.
Thank you for this explanation, I was totally lost on his explanation until you mentioned that these lines are acting as (near field) antennas. Otherwise I was lost in the weeds trying to figure out how you could shortcut a transmission line's delay.
I'd like to see more explaination about the antenna/near-field thing, I think that's missing in the video. Together with a diagram of a more complex, less geometric ideal, power transmission.
You will need time that enought to energy transmitted by resistanceless antenas of certain lenght to light a bulb. So you will need (x+1)/c or 1 which is smaller, seconds there the x is length of antenas required to generate power to light the bulb. Possibly it will be already shine if x is smaller than c/4.
This is exactly what i love and adore about physics: even the most fundamental concepts are so hard to comprehend, so that during the first few years of education we are told the most comprehensible "lies" in order to ignite the fire of curiosity and begin the search for what's really going on - fascinated by the mechanisms of the entire cosmos along the way. The ultimate way of teaching anyone to question, observe, experiment and evaluate. Great topic and really on-the-point video.
I was put off by the lies. I'm quite angry about it to be honest. Children are smart enough to understand this, we should teach them from an early age.
@@peepiepo agreed. I was a curious kid and learned a lot outside class. Learning old or bad information broke my brain especially when I would ask the teacher and show them I was right.
@@peepiepo I'm sorry if i put it wrong but i certainly did not mean we are being lied to while learning these concepts but rather encouraged to be sceptic about them so that we would find the truth - because they are not entirely understood by someone teaching/explaining to us - as being the building blocks of scientific understanding.
Just like in Atomic theory. Children are taught that nucleus is like the Sun and electrons are like planets, while in reality, these particles exist as probability wave functions.
I remember day 1 of EE being like, "so we're going to learn how to do circuits over the next couple of semesters and when you take EM fields you'll learn why all of circuits is kinda wrong." Turns out he wasn't just messing with us.
Are you suggesting that there might be a different way of looking at developing whatever it is circuits do? E.g. there might be different ways of directing energy field lines?
Circuits are not WRONG and they obviously work. But they are working at low frequencies where good old Kirchoff's Laws work fine. At radio frequencies and above other factors start to dominate.
It's great to see the Poynting flow argument reaching such a large audience! I always cover this in my college E&M classes. But I have to say that the claim that the light bulb turns on right away is pretty misleading. Consider the case where the circuit is actually open -- somebody cut the wire 300km away. By causality, the light bulb's behavior is identical in both cases (closed and open circuit) for t
Yeah, this video is really misleading in the way it presents the flow of energy through fields as a result of varying voltage as the main way that energy is transferred through the circuit. Not to mention that the "electrons move really slow" things needed to be elaborated on, in both DC and AC it is a chain reaction not too unlike a newton's cradle that moves the electrons further away and transfers the same potential (Voltage) to them. The electrons carry the potential to do work and then as they flow they lose that potential and regain it as they pass through different systems. I feel like this channel has been focusing more on being shocking then actually properly explaining the subject matter.
@@CrystalLily1302 no, the pointing flux part is fine. The em fields definitely carry the energy. The problem is with the idea that the light bulb "turns on". Just a language issue, not a physics issue
@@SamGralla it IS a physics issue. the energy the light bulb gets after "1/c s" (whatever that is... it's a meaningless quantity and hurts my eyes as a physicist and teacher) is way lower than what it gets after some seconds (not just 1). because the energy travels through the fields, but the fields are established by the current. and they travel as a wave (slower than c!!!) along the wire when it is switched on. to really let the bulb glow that fast he would have to use an incredible high voltage battery.
Adding onto this, the Poynting vectors shown in the illustration are the steady-state vector field. They do not reflect the reality of the EM field during the transient period as the circuit reacts after the switch is closed, which is what needs to be considered to answer the question. When one does consider the transient state, the result is that some small transient inductive currents do appear at the bulb, but the net power flow into the bulb remains essentially zero for the first second. Only after the change in voltage propagates from the newly-closed switch along the wire all the way to the bulb, do we finally see a persistent voltage drop across the bulb, which produces a steady current and hence a net power flow into the bulb. Furthermore, even just looking at the Poynting vectors from the illustration, the vast majority of the power flows along paths very close to the wire. So if we consider the opposite question, “What happens when the switch is turned off after it has been on for a while?” we get the answer, “Energy is still flowing along Poynting vectors close to the wire for an entire second after the switch is turned off, and a small amount of extra power continues to follow even longer paths in the space beyond, so the light stays on for at least a second after the switch is turned off.”
Considering how long ago we learned to harness electricity and create electrical circuits and how much misconception surrounds it, makes me wonder about other things we've misunderstood yet utilized nonetheless.
Yeah its very interesting to think about. I wonder if there’s any math we use in common practice that’s not completely accurate and would therefor disprove scientific theories we’ve accepted as being true.
It is fascinating how often heuristics can be just as good, or sometimes even better, than actual absolute knowledge. "Rationality for Mortals" and "Antifragile" are two books that talk about that idea, more so the former, the later kind of hits it tangentially.
@@johnwiand1167 yea i know how ya feel, but we already know that all established math formula give no certain answers without some margin of error, even 1 + 1 = 2, whatever that 1 of something is that your adding is likely not going to have to same number of atoms as the other 1 of something your measuring therefore your answer must be a decimal value. further, even electrons, protons, and neutrons have mass that can be calculated to some approximation but impossible to measure exactly which makes measuring anything exactly impossible.
Yes - a lecturer once told my class that we (humans) understand radio enough to make it work for us but 'exactly' how it works is still a mystery - to be fair that was 30 years ago!!!
I'm mildly confused... Provided that i tried using thw right hand rule in the "AC circuit" electric and magnetic field diagram he gave in 9:15... Did he not show the electric fields in the backwards direction around the battery and in the center region??... I mean... Whenever you apply the right hand rule around the source... You don't get the correct vector... For electric field downwards, the magnetic field should be into the page to get the required resultant vector.... As in the DC current demonstration he showed in 7:05 (for electric field being from positive to negative... Unlike the AC diagram he made) and 8:02 for the full diagram.... But around the AC source ... The arrows are backwards.. and even in the central region... Right??... I'm so confused on this..
Now that I've seen the same diagrams like 5 more times... In the AC diagram... He made the electric field lines from negative to positive.... Which has to be wrong... THERE'S JUST SOMETHING THAT EITHER I'M NOT UNDERSTANDING OR IS WRONG
The magnetic field is definitely there. Whenever I'm welding steel and the floor hasn't been swept in a while the steel filings align with my earth lead, which leaves some nice patterns!
That's not what's in debate. This is a given for a long time. It's the way the energy gets transmitted. Most think over electrons but we just have gotten it explained otherwise
@@felixisme @flawn I'm neither debating or claiming anything ground breaking. It's just cool that it's a visible example of the phenomenon and I thought I'd mention it for those who may not typically come across it.
Yeah, that's an oof on Derek's part. I was watching this and getting confused despite understanding the concepts. Basically, you can think of the flow of electricity like a game of telephone or passing a baton. A generator starts by exciting electrons at point A and that energy propagates through the wire to point B. The electrons themselves don't go very far, but they don't need to, since each one is a carrier. As the energy flows, it generates heat due to resistance in the wire and a magnetic field around that wire, which spreads out like an "aura" around it. This "aura" can align other wires nearby to the same magnetic field and thus passes that same energy to them without the wires being directly connected. This is why live wires can be dangerous and disruptive if not properly insulated from one another. This is also similar to how data can be transferred wirelessly via other kinds of waves like radio or other frequencies, but that's a different story.
@FlyingMonkies325 Yeah, I was just giving a very simplified overview about the concept in layman's terms. It has been a while since I've looked into the details, but point is, Derek went from debunking misconceptions right into Maxwell's equations. I can see why people would be confused with his explanation.
What a perfect name Poynting had so that his vector points in the direction of energy flow! Reminds me of how the Schwarzschild radius for a black hole was calculated by a physicist whose last name means "black shield" in German.
I hope you have a good day. I hope you get everything you've ever wanted this day or tomorrow. Keep going, and don't let anything get in your way. I love you.
I realize this will get buried under 25,000 other comments, but I can't help but wonder about a possible relativity paradox. Imagine that a person does create a circuit like Derek has suggested - a simple battery to light bulb circuit where the two arms of the circuit are an absurd length - but let's make each arm not 1/2 light second but a light year. Derek flips the switch and turns on the light. But...a person at the far end of circuit arm (1/2 light year away) wants to send a message back to Earth. If they momentarily interrupt the circuit from their great distance, wouldn't that turn off the light, and by Derek's explanation that would presumably be near instantaneous. This would seem to violate the principle that nothing - including information - can travel faster than light. I'm *not* suggesting that this thought experiment proves Derek wrong. I'm just wondering about how to resolve the paradox.
The information that the circuit has been interrupted would not be instantaneous, what makes you assume that it would? Even when the light bulb is meters away from the voltage source it still is a nonzero time for the signal to be received. Fields still can only transport information at or below c.
Maybe simpler : the circuit is 1 light-year long AND we don't know if it is open or closed at the very far end (which is 1/4 year away). When I push the switch, how can the magnetic field know in 1/300.000 second if it can transmit power or not?
@@LeCheneDeTele In this case the 1 in the numerator is distance, in the video its 1 meter i.e the distance from the source to the lamp ,in your question the units are light-years. Converting this to meters you might feel a bit better. I wouldn't blindly trust my calculations, but just treating everything classically I believe it would take about 91 days in your case for the lamp to turn off or on.
I have a degree in Mech Engr and my Physics E&M class was the only class where I was like “yeah I just don’t get this”. Sometimes I’ll wonder though if it really was that bad. This video just reminded me that yes, yes it was that bad.
yess @clarierich my whole Electrical engineering is flushed today.... it's interesting to get this phenomenon.... please clear my some dough ...so i can better understand this. so what we checked in ampere meter .... what is the meaning of current raised ... so how battery ..drain, why conductors overheated ..when current raise..if electrons doesn't flows...
@@lalitjoshi7152 Current needs a complete circuit to flow, in a conventional circuit, it's basic Ohm's law. Open circuit = maximum voltage, zero current. Closed circuit = maximum current, zero voltage. Negatively charged atoms (determined by electron surplus so we can say electrons instead) repel each other along the conductor in which they're present, this is why a thin wire cannot carry a large current - electron density. There's only so many electrons in a small space. In doing so it generates heat and yes, current flows. See my post below for where I believe this video gets it all wrong. The same electron as given by the battery is not the one that appears instantaneously to light the bulb. You in line ammeter is measuring electron flow, just how you think. Battery is drained by having free electrons removed, just how you think. It's energy was needed by the device in question to produce either heat or light or both. Conductors overheat because of electron flow, just how you think. Until I see good reason otherwise, I consider this video incorrect.
That's a great video about power transmission! I remember being surprised by that in the university. I really don't like the 1/c answer, though. While it's technically true that there will be some voltage on the lightbulb after 1/c simply because the electromagnetic fields generated around the wire will reach it, but it has nothing to do with them being connected by wires. In the same way, you can say that turning on this battery will "turn on" every single lightbulb on the planet. This is also technically true, because there will be some field generated by the battery in the entire space, and it will induce some voltage everywhere. Although its value will be negligibly small, as the magnitude of fields around the wire quickly drop with the distance from it. Only after 1 second, the proper connection through the electromagnetic mode of the wire will be established. If you replace the wire with an ideal coaxial cable (which doesn't let any EM fields outside the inner space between the two conductors), the answer will always be 1 second, as there's no leakage and thus no way for the lightbulb to receive the EM energy from outside the incoming cable.
Yes this video seems to have been deliberately constructed to be obtuse and misleading. Anyone with a decent understanding of induction can tell you some fllux gets to the bulb in 1/c, but there's an inherent assumption that the bulb needs some threshold of voltage to actually light, or by the same logic every bulb everywhere is always lit from background EMF
Great video on such a complex and controversial area of physics. It may cause people to argue that it is dangerous to be anywhere near the 'field' of wires or power source ( just like the controversy over living near 'phone masks!! LOL.
@Dalnore @Tim Sheehan, I agree but at 0:45, part of the assumptions he asked us to make is that the bulb will light up immediately as soon as current passes through it. The unfortunate demo of it lighting up that brightly is misleading but I’m not sure we would’ve noticed the difference in real time.
Makes perfect sense, but you’re just describing electro magnetic induction. I’ve never seen a short circuit from the magnetic field of an insulated conductor. Current still must have a path to ground to discharge energy, not through the magnetic field.
It's pretty easy to test this. Just take a 100m length of 50 Ohm coax cable arranged in a big loop with the ends 1m apart, connect a 50 Ohm pulse generator to one end and a 50 Ohm resistor across the other end. Use an oscilloscope with two matched probes to see how long it takes for the voltage to arrive at the resistor. If it makes you happier you can put an LED in series with the resistor and cal it a light bulb. The result will be about 0.5 microseconds and not 3 nanoseconds. Of course I know I'm talking to myself, there's no way Veritasium can read 30,000 comments.
1) Energy _is_ transferred by _em_ fields in the direction of the Poynting vector. 2) This can be considered to be energy transferred by photons. 3) Photons 'follow' many paths. In free space all paths are equally probable. 4) Photons interact with electrons in the conductor. When superposed there is an increased probability that these photons will 'follow' the path of the conductor. 5) There is a finite probability that some photons will traverse the path from source to sink by the direct route, taking a time (1 m / _c_ ms^-1) = (1/c) s. 6) It is more probable that photons will follow the path of the conductor. Such photons will take a time (L m / _v_ ms^-1) =(L/v) s, where _v_ is the velocity of light as affected by the electrons (left as an exercise for the reader), and _L_ is the conductor length from source to sink. Conclusions: Some energy _will_ reach the sink in (1/c) s, but the overwhelming amount of energy will take (L/v) s. If the light bulb takes an infinitesimal amount of energy to switch on then it will do so in (1/c) s, but if it is a real light bulb it would have to wait for photons to follow the conductor. Probably. But, as scientists do not decide by voting, has anybody carried out the experiment?
Good you mention photons. Tesla did all the experiments, yes only a very small fraction of the charge field (photons) reach the bulb, but also NO PHOTONS are stored in batteries, they are already all around us, the earth has a charge field, the photons come straight up out of the surface. The wires etc just give the field of photons a path they can take, ie go through the lightbulb wire, as photon density indreases, the atoms start to give off visible light photons as an atom/molecule can only recycle/process so much photons, the photons are spun up. The standard charge field photons are sub-infrared. To research anybody can read Miles Mathis.
I love the comment section. People put arguments and ask great questions. Some even put interesting hypothetical cases related to this concept of energy flow. It makes the video even more interesting. It makes me realize that there are so many things about science that we haven’t even fully grasped on.
Since the death of only 4 terrestrial tv channels in which to choose in Britain- of which two offered scientific shows on a regular basis , a lot of very young peoples’ slight chance of science igniting their imagination has been diluted . Then again I hear how Video Gaming now encourages all kinds of conceptual things so I’ve just ruined my argument...Sorry for wasting your time 🙄👍
@@Xentillus maybe, but even in scientific community, ideas are always challenged through conferences and journals. So it begs you to question your current perspectives.
@@Chris-rg6nm The electromagnetic field must still propagate through the wires at the speed of light, otherwise this is FTL energy that violates causality.
One correction to this video: The four shown equations...Maxwell himself never saw them. Maxwell used the formalism of Quaternions and he always wrote 8-12 equations. So it was very difficult to read the stuff. It was Oliver Heaviside, an autodidact, who later reformulated Maxwell's nasty-looking equations by using Vector Analysis. With that fairly modern tool Heaviside also managed to compactify Maxwell's 8-12 equations into 4, and gave both integral and differential forms. This led to the situation that since the 1890s the equations of electrodynamics were widely referred to as the Heaviside-Maxwell-Hertz equations. Around Einstein's era Heaviside's name was slowly dropped, unfortunately. Einstein himself always spoke of the Maxwell-Hertz equations. And later, Hertz's name was also dropped and all the name-fame went to Maxwell - not entirely deserved though from a scientific point of few.
True. Maxwell developed the entire concept of an electromagnetic wave, but his mathematics was cringey. Using vector fields, line integrals and surface flux integrals, Heaviside improved on the concepts of divergence and curl operators, so achieving the four famous equations that are so easy to apply. If you get inside the physics meaning of Maxwell equations, you can see there is no difference between the original equations and the versions improved upon by Heaviside, this is why his name has been dropped; the scientists of the time cared of who developed the concept. But. The Heaviside version allow everybody to conduct calculations, without the necessity to get deep into a difficult field of our physics.
Quite so. I'm the historian of science Derek talked to a couple of times in the video; I lay out the whole story of Heaviside and his rewriting of "Maxwell's equations" (to which he was led by his independent discovery, not long after Poynting, of the energy-flow theorem) in my book "The Maxwellians." But I have to say that Heaviside himself was fine with calling his set of equations "Maxwell's"; he regarded them as just a distillation of Maxwell's theory.
It's really disingenuous to say the bulb "turns on" in 1/c seconds. Yes, some energy does transfer in that amount of time, but the vast majority of energy transfer is in the EM fields around the conductors, not in the air gap between battery and bulb. This also completely ignores more nuanced effects like reflections due to impedence miss-matching or capacitive and inductive coupling. You could have avoided most of these issues by simply including a plot of energy/time for the light bulb, which would show the bulk of the energy arriving when a lay person would "expect" it to (ignoring reflections), 1 second after turning on. This is akin to saying "which way to gravity pull you?" and instead of saying the answer is down, or mutually up and down due to your mutual interaction with the earth, that instead gravity pulls you everywhere because everything in the universe is pulling on you simultaneously. Yes that's true, but it very much ignores the elephant in the room.
Thank you. Thinking the same thing. I think his falls into the "spherical cow" argument and completely ignores reality since its basically assumed to be acting as a big antenna of sorts with mutual coupling in the conductor and not acting as a normal wire would if it were laid in a large circle and propagation velocity and all the other sundry topics like characteristic impedance and such come into play. Sleazy slight of hand IMO. Thanks for removing the dislike button, YT.
And now that I think of it, this is analogous to the issue that my older LED lights up in the ceiling of my last house had. As they did not have discharge resistors in the capacitive dropper supply, there was enough capacitive coupling in the switch and wires to make them glow dimly as there was sufficient voltage, but very little current available. I would say most people would not consider that to be "almost instantaneously." More like "on", but in a very annoying way.
Ok, I think I've got it, if my assumption is correct: 1. The field needs to be established. This will take the 1s or 2s for the whole build up. The voltage is there then, but the current is not turned on, yet. 2. Then on releasing the current the energy will flow along the field, so only the distance battery and bulb matters. Correct? By initially physically connecting the Battery, first 1. happens, right? So 1 second. Otherwise the build up wouldn't have known if someone near the moon would have cut the wire long ago.
Perhaps if you think of all electrical cabling systems as RADIOS that just happen to use really long antennas and you'll get a more intuitive idea of what's going on here. The energy is always transmitted via fields, but the wire acts as a much more efficient wave-guide, rather than just throwing the field outwards in all direction.
No, this analogy is incorrect, but I don’t blame you because, as an electrical engineer, I can assure you that this video is full of errors. Antennas transmit data very well, but they transmit energy very poorly. For instance a 1,000,000 watt AM broadcast tower will transmit data over 100 miles, but you can safely stand within 50ft with no adverse affects. If your body was subjected to a tiny portion of 1,000,000 watts you would die instantly. This video is fundamentally flawed because the EM waves that propagate radially directly from the source dissipate very quickly and have negligible energy by the time they reach the intended target. If this was not the case, the power source could light the bulb without requiring wires. It is the EM field generated along the wire that brings the power source to the destination and provides sufficient power to light the bulb. I wish he would peer review these things before going through the trouble of making a video that misleads people. All the best
Technically correct but misleading. Electrical Engineer's take: The EM waves will take 1/c seconds to travel the physical distance because it's not traveling through the wires. You will see some current at the other end. The current generated EM waves and they have physically propagated to reach the light bulb. The Poynting vector is useless in this case as the battery doesn't even know the light bulb exists yet. Basically a misdirection here. This example is actually just two antennas initially before it comes a circuit. The current will be based on the inverse square law at the 1 meter distance. Since it's a battery, the initial current will be due to this and only after a second will the electric field in the wires reach the light bulb and it start conducting properly. (Assuming a perfect conductor)
Yes. That is how I understand it too. Because the wire is zero resistance (and assuming battery internal resistance is zero too) it basically acts like a transformer. Electron in the light bulb will move in the opposite direction of the electron in the battery.
@@louis5176 The electric field that travels from the battery is the main source of energy that you want to power your bulb with, the energy that travels through air at that 1*m/c is only a really small fraction of that. If you can power your light bulb with some microwatts of power, you can light your bulb, no problem, but he fails to say anything about this in the video.
I agree. I’m not sure it would be a “voltage spike” at 1/c though. As the long wires are parallel and zero resistance. As the voltage wave travels down the wire, it’s continually being coupled to the other wire. This would happen till the voltage wave “turns the corner” and starts it’s return back to the lightbulb. Assuming lots of ideal components I wouldn’t be surprised if the voltage at 1/c was a constant. Edit: that is of course till after 1 second where it won’t be constant anymore.
I suggest a follow-up which considers what happens if the wires at the far ends are disconnected. The first second after flipping the switch would be exactly unchanged! At first I thought this meant "clearly that means the bulb would be off". But the linked slides convinced me that the antenna mode is really big enough to power the lamp. Once you start thinking about the tips-disconnected scenario, you start seeing that this looks like one big wireless charger. The antenna mode of those is big, because the distance vs wire length is comparable. That's what we have, and I found it pretty convincing for this scenario too. If powered with DC it will stop transmitting power once the ends are reached and the fields settle, but until then there's enough antenna mode transmission to power the lamp. Would be a cool follow-up.
I would say things got mixed up badly here. Derek is not implying any antenna-mode transmission, his thesis is that, since the Poynting analysis of a steady-state DC circuit shows energy flowing through empty space into the bulb, then it won't matter if we broaden the sides of the circuit to an egregious length. The energy will still flow the same way, straight into the bulb. This is wrong. What you're talking about, and what was already discussed prior to the video in Derek's quiz, is the antenna-mode transmission. While it's definitely happening, the power of this mode is significantly lower. If you literally connect a 12V battery that's just about enough to light up the bulb, don't expect the same to happen wirelessly. There will be some signal there, but nowhere close to lighting up. So when Derek shows the bulb lighting up instantly, and also steadily glowing, that's not happening due to antenna transmission.
@@MarkoTopolnik I think you can also think about the super long parallel wires as capacitors, also explaining why the energy transfer starts right away, but very low, and grows over time. It's just an extreme case of every transmission line having capacitance and inductance and effects between adjacent wires.
I asked myself the same question but would like to see a more in depth analysis of what happens to the field at any point and time in the system and how the power of the bulb changes over time.
Question. If the wire is long, all the way to the Andromeda galaxy. And over there, a little green man will cut the cable and start transmitting a signal like a telegraph. After what time on earth will we notice that the light bulb starts to freeze? a) After 600 light years due to cable length? b) After a few nanoseconds due to the proximity of the battery and bulb?
It's disturbing that I successfully graduated high school with entirely wrong concepts. I could've died like that if possibilities didn't bring me here.
I think maybe you didn't emphasise enough an important point that might clear up some of the confusion. The motion of the electrons (current) in the wire DOES have an essential role, just not the simplistic one people usually assume. The electromagnetic field is the thing that carries the energy, but the moving electrons in the wire are a key part of creating that field. Otherwise you could get rid of the wire completely and still expect the light to switch on, which it obviously doesn't. For example, right after you close the switch, the electric field of the battery starts pushing electrons through the wire, setting up a current. This current only exists in the wire in the immediate vicinity of the battery at first, because signals are only transmitted at finite speed. But this initial current induces a magnetic field in its vicinity, which (along with the electric field) propagates through the air to the light bulb, causing it to turn on, as you explained. Meanwhile, the electric field created by the battery continues propagating down the wire (at finite speed), causing the electrons farther and farther away to start moving, until eventually the electrons in the entire wire are moving. As each part of the wire gets a current in it, it sets up its own magnetic field, which propagates through the air to the light bulb, giving it more and more energy until the entire wire is contributing. And although the light first switches on in a very short time in your example, it does not have its full light output until the current has had time to flow through the entire circuit. In other words, although it is indeed the field that is transferring the energy to the bulb, it is the motion of the electrons in the wire that is setting up the field that transfers the energy. This is why you can't keep the bulb on (at least past a certain time) if you remove some or all of the wire: the electrons will be pushed up to the end of the wire and stop and accumulate there, thereby repelling the electrons behind it and stopping all current flow in the circuit, which stops the magnetic field from being formed, which ultimately stops energy being transferred to the bulb. So the electron flow DOES play an essential role in the process, just not the simple mechanical role that is usually portrayed.
Right, this sounds pretty credible. So the correct answer is: yes the light turns on almost immediately, but only slightly. It then takes a second to reach full brightness.
To add to this, the magnetic field strength drops off with the square of the distance, so the contribution of power from the wires near the battery terminals is negligible.
Still doesn't sit right with me though. What if the wire loops were half a light second long as before, but then had a tiny break in the end of one loop? If this is the mechanism, it seems to suggest the light would turn on without there being a complete circuit.
So when we cut the wire, electrons starts accumulating at end of wire? If so, after one year should wire get thicker at end assuming DC power supply is constantly provided to this open circuit?
I see what you're saying there about how some energy would flow through induction in 1/c time, but I feel like that's a bit of a cheat answer. I think many of us know about induction and cross-talk, but that isn't what we are generally talking about when you say "what turns the light on". That would never be enough voltage for threshold current on the most efficient LED, nor the visible emission temperature of the lowest wattage incandescent. I agree with what sandman said about how you have to consider the wire as a wave-guide for the electric field.
Exactly. The wire is a waveguide for the EM field and the Poynting vector cannot overtake the EM field. Veritasium is wrong and his fraudulent experiment here gives a false impression that he’s right. Very disappointing.
@@lradmclovin9 The crux lies in the unshielded nature of the wires and how close they are to each other. I suggest you go through the additional slides linked in the comments
High school physics teacher here. I confess to teaching the "simplified" (i.e. incorrect) model of electrons being carriers of energy in a circuit, though we do extend this to the concept of fields once the fundamentals are understood. I am generally OK with lying to my students in the sense of "start with simple models, and then add layers of complexity as needed / as available." I literally had one of my students email me this video asking me if it is right, so I watched it. Knowing what I think I know about electricity, I agree with Green Lungo on this. I answered the question BEFORE the "assumptions" were stated. One of the assumptions is that the bulb goes "on" as soon as (any non-zero) current goes through it. If we accept this assumption then I agree with the given answer. But if you (somehow) managed to do this as described, with a real bulb (and superconducting wires etc.) then I am confident that no light would be seen coming from the bulb until the fields have propagated *through* the wires. To be a fair question with the intended answer, the assumptions should have been made very clear before providing the question (and multiple choice options).
@@winter-survivor No, you're not dumb. He teaches as professors do, which is not always good. Many professors have difficulty putting themselves in students' shoes. I'm not bashing professors, just my observations from 4 years of college.
Well well well, stepping into my territory, eh?! I shall make a video about this!!
Gauntlet thrown! I have my popcorn ready.
من فن شمام😂😂😂 فارسیم نوشتم چون میدونم ایرانی هستین
I would love to see your take on this
yo
I would love to see that!
Heres what i think, maybe it can help you form an opinion and make another great video:
I personally think that the light bulb would actually light up almost instantly, but not for the reasons described here. I think the cables are indeed what carries the energy, that transformers work by the magnetic field made by the primary side inducing current in the secondary, and that the reason the light bulb light up nearly instantly being that the charge in the wire builds up very quickly despite the wire being so long (this is assuming charge is conveyed instantly when there is no resistance, otherwise i would think that the bulb would light up after half a second). The wire gets charged, so there's a difference in charge at the light bulb. I believe that electrons do not have potential energy, the density of electrons in the wire is what carries charge, and charge is whats carrying the energy.
The telegraph cable actually disproves his take, in my opinion. If it was true, the signal would either never arrive, or it would arrive entirely normally. The reason it was so distorted is that the metal protection layer created a giant capacitor that caused all the distortions and slowness.
Also, if the energy was transmitted by electromagnetic waves, the inverse-square-law would apply, which it doesnt. If the electromagnetic waves stay equally strong throughout the circuit, that proves that the wires are what creates them, meaning they are what carries the energy.
(I shall update this comment whenever i think of new reasons)
I’m so glad this video exists. I use to completely not even understand how electricity worked, and now I still don’t.
lol
Same
I am still confused, but at a much higher level.
😂
Lmaoooo
WOW! I'm 80 years old. Started learning electronics in the Army in 1959. We were taught the "Right Hand Rule" in the study of inductors and transformers. Although we knew about the magnetic field around conductors we never applied that knowledge like this. Thank you for teaching an old man a new trick.
Nice
Wow u still study Great grandpa ji🙏
@@Abhinav-gu2ui Thank you. I love electricity in all forms. Except, of course, the CHAIR!
@@backlash00 do chairs really exist though
thats cap
Two atoms were walking down the street. One atom says to the other atom "oh crap! I just lost an electron". The second atoms says "are you sure?" The first atom says "yes, I'm positive!!!"
Lowkey fire joke for nerds lmao
😂
EE here; I think most of this info is technically correct, but potentially misleading in some areas.
For one, while it's true that energy is transferred in the space around a conductor, as opposed to through the conductor, the *vast* majority of that transfer is taking place *extremely* close to the conductor (we're talking millimeters, typically), due to both the magnetic and electric field strengths decreasing exponentially with distance from the conductor. So in reality, the energy being transferred actually decreases superexponentially with distance from the conductor. Now, in power lines, the ground is still a concern because it's a very long conductor, carrying very high voltage, at very high currents; it's a somewhat extreme case. Yet, even though the cable is *miles* long, we only need to separate it from the ground by tens of meters to significantly reduce losses over that long distance. Furthermore, the ground is only a problem because power lines are AC. If they were DC, you could lay the cable right on the ground, and you wouldn't get any significant energy loss.
Edit: see below, the dropoff is not actually superexponential, but the general idea that energy transfer is greater closer to the conductor is still accurate.
For two, the analogy of electron flow being like water through a tube is actually still accurate in the case of the undersea transmission line. The metal rings around the cable cause a change in electrical impedance for that section of the cable. In the case of water in a tube, this would be analogous to having an air bubble trapped in your tube. As a pressure wave travels through the water, it will suddenly hit this air pocket, which is far more compressible than the water (i.e. has a different impedance), which will cause the waveform to distort in precisely the same manner as the electric wave does in the cable. Some energy will pass through the bubble, creating your distorted (attenuated) waveform, and the rest of the energy will actually become a wave reflected back in the other direction. This is precisely what's causing the distortions in the undersea transmission line. There's a bunch of reflected waves bounding back and forth between all the iron rings that stretch and distort the original signal. (for the real electrical nerds, check out "time domain reflectometry", which uses this principle to precisely detect where a fault exists on a power line)
Third; yes, energy transfer from the switch to the bulb will occur in 1/c time (by the way, I think you could clarify this by representing it as d/c time, where d is distance from the switch to the bulb. You never really state where the 1 comes from in that equation (at first I thought you were implying it was a constant value, unrelated to this distance)). And yes, you do clarify that it will only be a fraction of the steady state energy. But I think you should stress that this would be an *extremely* small portion of that steady state energy. The initial energy that the bulb receives will only be due to the capacitive and magnetic coupling between the two long portions of the conductor. And in the case of wire separated by 1 meter, both the capacitive and magnetic coupling would be practically zero. This again is due in part to the exponentially decaying electrical and magnetic field strengths with distance from the conductor, as well as the poor electric and magnetic permiativity of the dielectric (air) between the conductors.
Fourth; addressing your question about "why is energy transferred during one half cycle, but not returned back to the plant in the other half of the cycle", I think your physical demonstration actually explains that perfectly. No matter which end of the chain you pull, there's something down the line offering resistance to the motion of the chain. Heck, you even get friction between the chain and the tube, which is like resistance in electrical conductors. However, if you attached a sort of clock spring to your wheel (such that the spring always worked to return the wheel to its at-rest position), you would indeed see some energy returned to the power plant (you) on the second half of the cycle. This is analogous to powering a capacitive load with AC.
If the energy is transferred in the space extremely close to the conductor, and he said that electric field needs to extend through the circuit (at 6:15) , does it mean that he's wrong saying that the light bulb will turn on almost instantaneously (at 11:45)?
This should get more upvote, this is what I learned in college, also EE major here.
That's a really complete comment. It touches most of the points that bothered me. Thank you.
One frequent things I've been seeing on the comment section was the idea of cutting the wire midway through the experiment. From what I understand, I reckon the electric field will just propagate through the wire until it reaches the cut ends; at which point there will be no current and the magnetic field will drop off and no more power will reach the light bulb, correct?
+1 on the technically correct but very misleading train. Everything he said was true, but it implies something that's not quite right.
I'd love to see some calculations showing the current across the bulb vs time for the very long wire case shown in the video. If anyone knows a place where that's been done that'd be great!
It feels like a lot of the misunderstandings about this come from the classical simplifying assumptions that are made to make lumped element circuit modeling easier. Things like assuming that there's no wave propagation time. This means that the intuition gained from lumped element circuit modeling can fail us. This certainly gets me. The full time dependent maxwell description of this problem is much harder to reason about. The problem as posed seems like a good application of distributed element modeling
The other thing that surprised me was the professors talking about how there isn't energy in the electrons. Now this is also technically true as well, in as much as energy is mostly book keeping, but there's definitely an energy change associated with moving a charge in an electric field. You can turn the electrical potential energy into a kinetic energy of an electron. In an electron beam for example. And I feel like they both know and kinda say this, but the way Derek has presented this seems to imply something a bit different.
If misunderstood something then please let me know.
@@joshharrison2657 Veritasium in last few years summarised in one comment
I feel like a baby who just realized mom and dad don’t really disappear during peek-a-boo
😂😂😂
It's light, Joe, but not as you know it! (Or thought you knew it)
okay but they still can't see me behind the ankle-high curtains
Your dad might have been disappearing a little bit into your mom... so you weren't totally wrong
Hey, i'm very aware that you dislike people like me, but theres no other way to stand out really. I released a new song which you can find by searching "Thnked - Forever" or through my profile. I'd appreciate it tons if you could drop in some feedback as well. Thanks in advance 💗
I'm 66 years old. As a child, we lived near large transmission lines in a rural area of CA. They passed over one of our pastures. We had a small water pump shed near the base of one of the towers. I "helped" my dad bury the power wires to the pump shed, 400 ft. from our barn/shop when he was installing a new pump. My dad used pipe strapping tape to mount some fluorescent tubes inside and outside of the shed. Everynight the lights were always on and I asked him why. He took me out to the shed, and asked me if I felt anyything... I realized that the hairs on my arms felt tingly, and I felt something in my ears. He explained about how such high voltage cables as above "induce" a magnetic field way around the big cables, that's what gives me the feelings, and what makes the tubes glow like they were wired to something. That had to have been 1960 /61- as I had just started 1st grade. He drew some sketches to show how "he thought" it worked. He gave me a basic electricity book and quizzed me every once in awhile. His sketches looked just like your graphics. I guess my dad WAS a lot smarter when I was younger. LOL
This is a great story, thanks for sharing 🙌
Electric fields. Electric. Magnetic field can not light up a tube. Unless you create a loop which turns magnetic back to electricity.
@@marko_z_bogdanca how it works.dont know.but a tube will always light round high voltage
@@marko_z_bogdanca They are the same, it's just a question of the point of view, it's relative. 😉
Yeah. My dad used to tell me a similar story: he told me that fluorescent tubes were constantly on near a big AM antenna and they used it to illuminate their shed also!
Anyway, that's not what Derek told on his video. There is two ways of transmit electrical power: wireless and wired. The light bulb will receive a very tiny little amount of power due to wire coupling (electrically or magnetically coupled). But in this case the power is transmitted in a wired way, not wirelessly. Transmission lines like the one over your heads do irradiate a lot of EM field and can be picked up by items that could work because it uses very little power (compared to the amount transmitted on the lines). But it's wrong to conclude what Derek concluded on his video.
I drank too much to be watching this I'll come back tomorrow morning
you never came : (
@escriticapop it's nice to know someone is looking out for me when I get home I shall return to this video
@@cuhrt1248 did you?
@@GiovannivanBogaert yeah not being drunk while watching it made me realize I'm literally studying electromechanics so I know how it works
@@cuhrt1248 This made me laugh so hard
I teach physics at the University of California, San Diego, including this very topic. Within an hour of watching this, I set up the experiment, and got the result. I have photographs of the experimental setup, and of the oscilloscope traces. I discussed the results at length with a physics professor friend, and we agree on the explanation. In fact, the load gets (nearly) the full voltage (almost) immediately; there is no (visible) ramp-up time, nor delay through the long wires (delay < 10 ns). This is fully consistent with transmission line theory that is well established for about a century. Dr. Muller's Veritasium series is great, but in this case, there are several claims that are incorrect, or at least misleading. There are many subtleties, and I cannot do them justice in a comment. I would enjoy talking with Dr. Muller to clear these up. For reference, I have a BS in Electrical Engineering, a PhD in physics, and I am author of "Quirky Quantum Concepts", an upper-division/graduate quantum mechanics text supplement. This is my first TH-cam comment ever.
Update: I love the Veritasium series, and I have learned a lot from it. To respond to some replies: I chose the simplest case, which I think illustrates the point that power can reach the load without going the whole length of the "wings." The analysis link below the video covers the more-complicated case. My "wings" are 50' hardware store extension cords. My propagation test confirms that coiling them doesn't matter, as expected. My analysis is fully transient, and the circuit transits to steady-state DC over time. Resistance can safely be approximated as zero, but inductance and capacitance cannot, as expected by theory. My load is 270 ohm, roughly the on-resistance of a 50 W incandescent bulb. The characteristic impedance Z ~53 ohm, which is substantially less than the load; that's what's needed for the simple case of near full response nearly immediately (the load is _not_ matched to Z). In this case, the wing capacitance dominates the behavior.
Consolidating my previous reply: Examples of subtleties: Do two electrons repel each other? (a) Most people would say yes, and I agree. But one could argue (b) No, one electron creates an electric field, and that field pushes on the other electron. This is also correct; it's slightly more detailed, and from a somewhat different viewpoint, but (a) is still correct, as well. But (c) In calculating the force of (b), we use only the E-field from one electron, even though we know both produce E-fields. To use the full E-field, we have to compute force with the Maxwell stress tensor; this is also correct. There are multiple correct views one can take. The video's chain analogy is very good, and correct. Separately, a few replies have hit on the most-direct (IMO) explanation: the capacitance in the wires provides an immediate, physically short path for the electricity to reach the load. The path of current changes over time. Your gut might tell you that the capacitance is too small, but a quantitative transient analysis using standard circuit theory matches the experiment. Special Relativity still stands. More subtleties: characteristic impedance, etc. I do similar demonstrations in class, so I happen to have all the equipment and experience ready to go.
When the first comment is the best comment.
You know the earth is flat.
@Tim Moles - 😂 that's the exact right thing to say when the scientific jargon resembles an extraterrestrial language.
So...why do we use wires? Couldn't we do without wires in theory, to transmit energy? Basically it needs nothing in between the switch and the bulb, why does he use the wire if it really worked like he explained in the video...?
No delay? Are you saying information travels faster than light, and that you've measured it?
And here I thought all vectors were pointing.
With both direction and magnitude, oh yeah!
Wait till you hear about Killing vectors :-)
Pointing and poyntng are different👍
I C what you did there
(0,0) would like to have a word
I am a lowly aircraft electrical technician and mechanic. But from troubleshooting aircraft systems over the years, a fuzzy picture started to form in my head almost exactly like what you illustrated. And I've used that image to do mental checks in my head against where power is going, and if my diagnostics are correct or I have my test equipment in the wrong place. This video completed the puzzle in my head, and I think a lot of people in the blue collar world who work with electrical systems every day without ever defining the knowledge they've learned from it will appreciate seeing this video.
Yes, most people in practice think about electrics as about hydraulics. Closed system where medium (electrons) runs around and does useful work. Pump = battery, power supply, hose diameter = voltage, pressure = amperage, current, viscosity = resistance, valve = switch, check valve = diode, hydraulic motor = motor, accumulator = capacitor, etc. This way of thinking will allow you to solve vast majority of electrical problems.
But the reality is much much more complicated.
I think he's playing games with us rather than teaching for clicks. Electrons move and they generate EMF, they're 2 sides of the same coin and can be looked at from eitherside.
Nothing wrong with what he said except it doesn't invalidate the otherside, that part he said about it being purely academic, he knows what he's doing.
That's why he's getting more dislikes than usual.
Dear SyTy, I sincerely suggest that in your work you follow the procedures established by the aircraft manufacturer and NOT your feelings and impressions you're getting from youtube videos, even ones of such respected authors like Veritassium. As a pilot, I sincerely hope you do.
@@cheburatorish he's loosing respect from me with every viral video he does. He's a youtuber first now, teaching isn't his primary agenda anymore.
@@Commander_ZiN Wait, you're still seeing dislikes? I thought TH-cam got rid of them. I certainly can't see them anymore. I suppose they may be 'phasing' it out? Not sure what the point of that would be, though.
Trained in the military about electricity, using the water hose analogy. pressure=V, Flow=A , hose diameter=wire gauge=R . This answers a lot of questions Thanks.
Of course I find this video now… around 6 months ago I got into a small debate with my electrical engineering professor over a topic very similar to this. Everyone in the class seemed to be on the professors side which I guess makes sense but then the following week our professor walks into class and tells me he thought about what I was asking and had looked into it.
He walked up to the board and showed some of the similar stuff you did in this video and proclaimed I had actually been correct and my original question that countered his previous discussion he admitted to the class he was in fact wrong. This was the first time in my life I had such a crystallized idea of what someone that was truly intelligent acted like. He wasn’t upset, frustrated or hurt that his initial statement was wrong because he didn’t care about being right, he cared about the truth.
I know it sounds corny to say seeing someone look for confirmation instead of affirmation changed my outlook on life but it really did. Never before had I seen some so openly question their very own view and search for the truth rather than search for what backs up their view or idea. Great video, as always
Epiphanies can be painful, but we make them so. Your professor is clearly a devout scientist! Congrats to you both!!
That’s a great story and lesson! ❤
wanting to know the truth and rethinking you own knowledge, just to find out you've been wrong is a true sign of high intelligence.
👏👏👏
thinking that one is always right, on the other hand, is not
Reminds of when I was in 8th grade I argued with my elective science teacher about bullets firing in space his argument was based on the lack of oxygen and I knew that didnt matter since they can fire under water which doesn't have usable oxygen for combustion. I also liked guns growing up and its simple firearms knowledge that the use of self oxidizing smokeless propellants was a huge leap in their development. He reacted the opposite of your professor when we googled it and I was proven right.
"Power and Logic are not related." (-me)
People concerned with logic aren't concerned when they're wrong, but people use _use logic_ to wield power get upset when someone else is right - their power is tied up in being right.
(Note: that's the core to mansplaining too - explaining to assert dominance, not to bring equality of knowledge.)
The fundamental law of physics: electricity disappear if you stop paying bills.
No its the laws of capitalism that govern the energy flow
Nikola Tesla said energy can be free , but are we willing to
hahaha
No
You can create electricity if you want
Many still it to
:)
Unless you own a solar panel
After watching this video I can confidently say I understand less about how electricity works than I did before.
Try opening your mind sometime ?
Yes, same for me. It is a new concept for me, so I am so glad about the video but unfortunatelly many questions raised that are not covered by the video...
Because it does touch on a more fundamental 'weirdness' (not really) about the universe that you didn't know about before.
@@alanwannemaker2518 But what if the information in this presentation is in error? How does that profit an individual to spend a lot of time and mental energy trying to understand something that may not be true. It may be like global warming, all garbage but we still won't quit talking about it.
Because he's lying. He's using misleading editing with the professors to try to make it sound like he's saying something counterintuitive. He's cheating the viewer.
dude i cannot express how thankful i am about this video, i asked multiple teachers as to how AC current carries energy when the net displacement by the electrons are zero, like there are electrons that wont reach our home provided the "wire" is extremely long.
and so now that i've watched your video, this greatly aided me in understanding AC current and DC current
That's really not a problem. The net displacement of the teeth of a hand saw is also zero, but it transfers energy the whole time it moves, in both directions, just like electric current. This video is misleading.
Mind-blowing. Thanks.
Impulspower ist the Secret. Elektrons move with less m/s but the Impuls Transfers the Power Like Dominos bricks
I'm an electrician from the UK.
This theory can be proven by holding a florescent tube near a power line. It will glow. My family didn't believe me so I showed them. So glad you explained this in a way they understands fully. Thankyou. Very clever.
A total physics noob here, Im sorry if this is a really dumb question: But if a florescent tube can glow because it gets energy from the power line, why dont we get electrocuted just by standing near a power line?
@@shiraishichan3944 same doubt 🧐
@@shiraishichan3944 I feel its all about distance and what you are wearing. I'm sure if you got close enough with no clothing and a direct line to ground. You may experience ark jumping. Its a very good question 🤔
@@shiraishichan3944 hey EM waves not harm us ( like light not hurt you when it falls / passes through you) here energy is transferred by EM waves from the source to the electrical device which receive and convert to their known energy ( electrical)
When you keep a fluorescent bulb near it takes those energy which was carried by em waves
Same concept using in a current detector in a wire , we actually detect the em waves around wire which have more intensity near it
There is a difference between holding a power wire and stands near it
but wait.. how can that be possible? what if someone cut the wire at the end and then at the same time you turn it on? does it still turn on instantly, but then "realises" 1 second later that the wire got cut and turns off again? I guess from your perspective, you would be turning it on first, and then from your frame of reference you would PERCEIVE the other person cutting the wire only 1 second later, despite them doing it a second earlier from their frame of reference.. edit: but what about signal reflections? what are they then? what the heck was I dealing with with ADSL ports having the signal reflected back to the first wall socket from the disconnected wire leading to the 2nd wall socket? and why do RAM traces on motherboards suffer from reflection?
Hold up this is a really good question I'd like to know what happens too
This is an interesting question
You perceiving something a second later does not mean it did not happen a second ago. So if at the time of turning it on it gets cut, its not gonna light up.
How would that work for the cutter? He wohld cut it, and then he would perceive that the light would be switched on a second later, so he would perceive it as being turned on a second AFTER his cut.
Both are wrong as its not about the observer. Its about the event itself.
This question should go up
if we cut the wire then the tow wire connected to the battery act as tx antenna and the other act as rx antenna so the bulb will emit only a flash .
I know you predicted pushback, and with good reason, so here it is. I’m not saying this video is wrong, but at best, it’s incomplete.
First off, the fields can’t intrinsically be separated from the flow of charges as if the electron drift isn’t significant. For the magnetic fields to permeate free space in the first place, the charges must undergo acceleration to create them, and if you cut off the switch, the fields would collapse without the current. If I turned on a fan next to a piece of paper and the paper flew away, would it be accurate to say that the air alone did the deed? Sure, the energy that moved the paper was transferred to it by the air, but neglecting that the fan moved the air in the first place would be a glaring omission.
It’s also essential to remember that the Poynting vector itself is DERIVED from the continuity equation (local conservation of charge), and what it represents is the interplay between the energy transfer among the fields and the movement of the charges that generate them. In other words, fields don’t carry energy on their own without the movement of charge. Also, the vast majority of energy transfer in the fields happens extremely close to the wires, and the graphic that you’ve given of these fields taking such wild departures away from the circuit ignores the infinitesimal magnitude by which this happens.
With regards to your experiment, the following should be noted. Yes, there would be some current flow instantly with the closing of the switch, but only because the electric field in the conducting wire has had time to reach equilibrium along its length. If instead of a switch, you connected the wires to the leads of the battery directly, the propagation of the electric field along the circuit would occur at a speed less than that of light in free space. Lastly, I challenge you to explain the energy release from the actual light bulb that doesn’t involve electrons flowing through the filament.
Also, I posted the following as a reply further on in this thread, but I'm putting it here because it's important. The power (energy per time) that a circuit puts out is always IV (current times voltage). This relation makes no reference to fields of any sort. Now, it is absolutely true that the electric and magnetic fields carry the energy - the current does not - but when one takes the spatial integration over the Poynting vector, it always reproduces the power law P=IV. The fields carry the energy, but the current generates it. You can change those fields in a million different ways and the circuit will behave the same. For example, wrapping the wires in a grounded sheet of aluminum foil creates shielding, which is how high transmission data cables such as CAT6 or COAX reduce noise and capacitance between wires. You could say that they contain the electric fields within the space of the insulation. You could also coil the wires into an electromagnet. However you reconfigure the fields themselves, the fact is that the overall power dissipation of a circuit depends on the current, not on the field strength, and to trivialize this fact by focusing on how the energy is carried is confusing and misleading. As with my earlier analogy to a fan blowing air, the energy may be carried away by the air, but the amount of that energy depends solely on the power output of the fan.
Ultimately this video has some good information, but it is also extremely misleading, and I caution people to take any claims that “they way you understand things is false” with a grain of salt. Usually, there’s more nuance than that, and as something of a cynic myself, I think it’s often a form of clickbait. I encourage interested viewers to look elsewhere for the full picture of electrodynamics in all its beauty.
what would you recommend to read to understand it ?
I second Manuela's question. Apparently, you'd first need a general education in physics and only then would studying electromagnetism make proper sense. What would you recommend?
@@ManuelaNChannel @wii3willRule I'd argue without a fundamental knowledge if calculus and/or differential equations many textbooks on this subject would go over anyone's head. Assuming you have such a background, a text on microwave circuit theory (I prefer Microwave Engineering by Pozar) would help paint a slightly better picture of the EM processes occurring inside of a wire. A book like this would also speak on the applications of such methods in broader sense.
Ok, thank you. I had a sense that there was amore to the story, and that Derek's explanation was somewhat lopsided.
I agree, Derek purposefully took a topic lecturers debate about and gave us just enough fuel to start an internet bonfire and not enough knowledge to put it out.
He did this on purpose and we'll need to wait for the next video to find out why.
This isn't educational, but an experiment on who fact checks.
There's nothing wrong with poynting's therom, but also there's nothing wrong with traditional Electronics Engineering.
The only thing wrong is his transfromers and undersea cable explainations and then at the end pretending electrons don't have anything to do with it.
His entire electron flow was also missleading, sure it's slow and AC goes back and forth but think of Newton's cradle, one ball makes the ball at the end move without ever the traveling to the end.
Transformers excite different electrons on the other side, think of it as it's own generator if you will.
The undersea cable had issues with inductance that can be explained traditionally.
It's like looking at 2 sides of the one coin, neither side is incorrect they both represent the coin. However if you want to design a ciruit you'll use math that follows the electrons.
His video was misleading at best and the dislikes are worse than his usual. 176k likes and 4.3k dislikes and most people probably can't see them.
I feel like it's a social experiment or he's just desparate for views.
There's plenty of resources online for classical electron flow, not so many resources on poynting's therom, I would of expected far more and I couldn't find a single other resource pointing to electrons not doing the work. Derek has sources but not going to go out and buy those books without a better reason as to why.
I love learning when its not obligated upon me, this was genuinely fascinating
I hope your channel only grows from here, you deserve it.
I’ve been an electronic technician since the 90’s and I remember one of my electronics instructors explaining this to us and it still blows my mind all these years later. Fascinating video, thank you for posting.
Suppose the bulb in the diagram was at the middle of the top line of the square of wires would the field arrows that were in the diagram still move towards the lightbulb?
I think it is a bit easier to picture when thinking about microwave Radio Frequency (RF): they literally have wave-guides that look like steel pipes. From the shapes of these "pipes", it is clear that all the energy is in the empty space inside the "pipe" rather than in the conductor on the surface.
I am not convinced. I think the E field needs to propagate along the wire to have enough intensity to light up the bulb. Otherwise, if I disconnect the bulb from the wire, according to the video, it seems the light would still be on, which cannot be right. Would you might help me understand this?
Can you explain something? When I switch my house light on, what distance is taken into equasion? From lightbulb to nearest transformer?
@@Megalolio From the switch to the light.
I think the best part of this video isn't just the information it presents, but also the conversation it sparks in the comments! People asking questions, people trying to understand what's being said, and even people providing counter-arguments in certain scenarios where what Derek explains doesn't seem to match up. I think having civil discussions helps a ton, thanks Derek + the Veritasium community! This video and the comment section is genuinely interesting to go through
People just figured out that he is wrong 🙂
@@markmd9 where's your evidence?
I think he is being somewhat intentionally deceptive/vague in the video on purpose to cause this :P
He's not wrong, it's just a weird perspective.
I'm wondering if you even watched the video before you posted this self-aggrandizing waste.
@@markmd9 He is partially correct and partially wrong. There will be some small energy transfer between the bulb and the battery in 1/c but the bulk will happen after more than 1s.
The central issue here is the muddy definition of the bulb being "on". It obscures the fact that there are two separate events in terms of current in this scenario.
1) After 3.3 nanoseconds, the light bulb will experience a very tiny electrical signal. This is true even if you cut the wires, and has more to do with antennae than circuits. (Hell, you might as well say the light bulb will turn on *before* you close the circuit due to the ambient radio signals)
2) After 1 second, the light bulb will experience the full voltage of the battery like it would in a "normal" circuit.
The energy does travel along the outside of the wire, but the vast majority of it stays very close to the surface of the wire. Thus, when talking about energy propagating in circuits in any real sense, it does need to travel the entire length of the wire.
Very simple and clear explanation! While the whole video confused me, this simple 3 paragraph explanations made it very clear.
Thanks
So if the only switch is at the wire extremity (half a light second away) and is open, then the capacitors are charged and in steady state => light is off
When I close the switch (half a light second away) then the light will take half a second to turn « on » right?
Yep! The visuals in the video even show this. While a small signal magnitude will cross directly, most of the flux vectors do actually have a length close to that of the wire. Hence why none of the Profs at the end wanted to guess what would happen in a real experiment because none could guess the "on" conditions
@@christiansimon399 you're going to get a signal quicker than that. Think what the OP said about antenna. It's a direct path. In terms of the "full" voltage, then yes, it will take longer
@@christiansimon399 Interesting question. I don't know exactly how the wires would behave in terms of the antenna effect in this example, but we can neatly step around that detail!
In your example, the switch is half a light second from the bulb. So due to relativity, any effect of you closing the switch *must* take (at least) half a second to reach the bulb. So to the extent there is still an antenna effect, it will take half a second to reach the bulb. Which is about the same time it will take the full voltage to reach the bulb.
Thanks, Eric P. Dollard pointed this out years ago.
Glad you're showing this❤
The part about AC was mindblowing. The Poynting vector is S = E x B but if both E and B are reversed, then S = (-E) x (-B) so the energy flow stays the same!
For me, that was one of the only parts where I was like "oh, yeah, I know this one!" ahahah! Everything else was mind-blowing!
The visualation was the only why I would have understood that concept. Seeing the diagram, I immediately recognized it as just rotating the circuit along the axis. People who can look at numbers and gleen the same information are wizards as far as I'm concerned.
I absolutely read SEX the first time I saw your comment. Had to do a double take, lol.
wat
@@FranciscoPower same lmao, I'm still shocked for everything else, I guess I have to watch the video a few more time
Still having one doubt: I understand that energy doesn't need to travel through the whole circuit, but how does the light bulb know it's a closed circuit when you flip the switch? Let's say the wire is cut off somewhere very far away from the switch and the light bulb, information should still take time to travel instead of instantaneous. Unless it will work even if it's not a closed circuit, but this doesn't make sense either. It's like I can just flip a switch near a light bulb and it will magically work without a closed circuit. I know it may work without a closed circuit like a transformer, but this setup is not like that at all.
Also, mentioned by Rick K in the comments: If this is true, then why don't we use that effect for "faster than light" data transfer? If the light bulb "reacts" to the switch almost instantly, that would mean that the "information" transferred with the flip of the switch is also transmitted instantly.
I asked basically the same question, hope somebody explains this
Very interesting take, can't wait for the expert responses.
I have the same concerns, definitely an interesting topic
The information still dont travel faster than light. it just takes a more direct way. We basically already transmit information this way with radio waves. I am still corious about the explanaition of the first part of your question tough...i dont grasp that either
dude do you realise, the speed of light is like, mind numbingly fast? it might not be instantaneous but it's the closest you can get to instantaneous!
This channel is impressive. You are an amazing teacher and have put together an outstanding video. Nothing about this video feels cheap and generic. Thank you for the authenticity that you bring.
I really got something out of this!
This video: "Forget everything you know about electricity."
Me: "Way ahead of you, as I already know nothing."
Hahaha exactly what I was thinking
Me too. :D
I know that I am intelligent because I know nothing.
- Socrates.
None of the above
As said in the video most if not all doesn't know the real thing even the experts in the field.
Honestly, the analysis from the professors made a lot more sense to me than the video just from a small clarification that I didn't catch from this with one watch, and had left me very confused. The energy most are generally used to seeing from a long, wired connection is from the "transmission line" current, but the energy being talked about here is from "antenna current," and the two modes of transfer, along with major differences in voltage that actually reaches the bulb by either type, felt like important info to leave out. The implication I got from the original video was that the length of the conductor did not matter at all for this model, but the reality was just that the 1m distance in the math, and specification of "any" current, hid the conflicting nature of two modes.
So, from my corrected understanding: The "transmission line" current *would* take one second to reach the bulb, through electron to electron EM field interactions in the wire, it's just that the "antenna" current can travel there first, because of a lack of shielding, and the misconception/lie here isn't so much a misconception/lie, but a lack of information on additional modes of energy transfer.
It felt like this video was more focused on becoming a popular, trick question via omitting information, rather than informing people on new or misleading information, which is not something I would/could say about any other Veritasium videos I can recall, and I do not like to say.
Sounds like the one on autonomous vehicles. Thank you for clarifying what was missing here
Agreed entirely. This felt more like a parlor trick gotcha rather than any deep (causality-violating) explanation of a fundamental misunderstanding around electricity
Reviewing the comments, I see that many others share the misinterpretation that I had, and I feel that is not a good reflection on the clarity of this video, with many accepting that interpretation as fact even in the case of others pointing out causality issues. If I am wrong, I will accept that, but this is my current opinion upon what I have seen as of now.
well I mean the question asked was how long till the bulb lit up. It doesn't matter about how long the current takes or anything else. just the bulb. I think you just didnt listen to the first words of the video.
I guess the next question would be what's the ratio of antenna to transmission line current in standard environments, how significant are the two sources.
man, I'm generally a fan of yours, but I do hope for an errata on this one.
You're absolutely right regarding the fact that the energy is propagated by the fields, and not the wire. But your explanation (and specially the answer to the '1c*s wire question') hides the importance of the wire: IT GUIDES THE WAVES. Without a wire to guide the waves, you can't propagate the energy at all. Meaning: the state of the wire is important. If the wire gets cut, the energy won't be propagated, as common experience shows.
So with the long wire situation, the fields will take time to propagate based on the length of the wire. Not because the energy is propagated by the electrons, but the wire is what guides the waves from the source (battery) to the load (lamp). Think about it: if the energy arrived 1/c seconds later, what's the point of the wire?
Of course there are secondary effects (through capacitance, inductance and radiative effects), but these mostly die out at a time scale much shorter than 1 second, and are much, MUCH, less capable of transmitting energy than the conductance effect which is capable with the wire. You mentioned this briefly, but your brief explanation (and the graphs you show) implied that you were talking about transients (since you said it depended on the impedance), but transients also only travel at the speed of light.
A cut wouldn't let the wire form fields at all
> Without a wire to guide the waves, you can't propagate the energy at all.
Not true, this is exactly how antennas work!
Did u not read the top comment?
@@adelelopez1246 yes, now compare the efficiency between a guided system and a radiative system. You barely feel the fields when they are radiated.
There are wireless energy solutions though. You can transmit electricity wirelessly.
The light turns on at 1/C? If that were true wouldn't you be able to setup two circuits and communicate between the two ends faster than C? Seems to break a few theories...
Exactly my first thought
I really like how you post a poll first and then post the video with in-depth explanation later, keep at it. :D
Oh where did he organize polls
Great way to get a ton of engagement and boost the video in the algorithm, too.
@HARSH MAURYA It comes up when you’re on TH-cam app and subscribed and all notifications allowed.
@@harshmaurya7639 community poll of TH-cam
@@harshmaurya7639 you can check his community tab in his channel
As a tradesperson who has created and installed many home wiring circuits, wired up car stereos, installed lights and even built circuit boards; you have shattered the sense of pride and accomplishment in what I've done by pointing out I didn't REALLY know what I was doing. I'm going out to rub two sticks together in order to claw back some small semblence of human ingenuity.
You and i sir, i feel that everything in my life is fake and i have been lied to all my life
To be fair, this is very misrepresented in this video and arguably incorrect even though everything stated is actually true.
Ultimately the power is inducted into the light as the em field generated around the battery and outgoing wires propogates outwards at C. IE: its basically the same type of inductance you see in an air gapped transformer where current and voltage are generated in the light by the inductance of the power from the battery after 1/c seconds. So yeah technically it is "on" (sort of at an extremely minimal state though it would not be visibly on). With what we classically think of as "turning on" occuring at 1sec once the electric current also travelling at c (along the longer path) reached the light through the conductor.
Don't feel to badly. All this desktop research about power transmission is really interesting but how many of "them" have wired the same number of houses successfully as you have?. Still I am grateful for the knowledge shared here.
I got the same rude awakening but once I accepted it I feel much more excited about the possibility of free energy from tapping the earths natural magnetic force and static electricity. I believe Tesla’s experiments in this field we’re grossly underestimated ...or purposely sabotaged.
All we need to learn now is how to throw the “on” switch to power our homes, cars, airplanes etc.
We already know we can run cars trucks and airplanes on electric motors. All we need is to find the vector of the flow to find where to put the “on” switch.
@@Peter-gq8uh I agree. I’ve watched electricians wiring new homes and how fast they move through the room. The wire literally seems to become molten and flow into the switches and through the metal boxes into they’re receptacles. They become so fast you hardly see the insulation flying off the ends of the wire and they’re already connected to they’re receptacles.
Understanding the mechanics and engineering of something perfectly and making it work does not involve the science of electro-magnetic flow and chemistry, physics and other scientific facts. And thank goodness for that or we’d still be living in potato huts.
Speaking as an electrical engineer, electricity is the closest thing in to magic that everyday people deal with.
I deal with conceptualizing electricity and electrical components every day, and you're kind of forced to think of amperes like your chain analogy, voltage like water pressure, transformers like gear boxes, etc.
But you have to keep in the back of your mind the whole time "but it's not water mains or a gearbox, it's electricity". It's simple up close but a whole other different thing when you try to think of the whole power grid at once.
My advice to laypeople? Learn what you can, and marvel at the physics of electricity with me! ...But call a professional if you need to wire a car charger into your garage.
word!
I can almost guarantee that the electrician who wires your car charger doesn't understand much of this either >
@@nathan87 electrician here; we’re not labourers or handymen, we’re trained in electrical theory and hold technical qualifications. We may end up slightly dirty at the end of a work day but we’re well paid and quite knowledgable 😊
I am exactly the kind of person the wise man was referring to when he said "A little knowledge is a dangerous thing". I'm exactly the kind of person who would learn the basics and immediately think they could DIY their own car charger, lol. This video, and indeed this comment, are good reminders that I don't know ANYTHING about how electricity works, no matter how many cool analogies I know.
@@nathan87 But he will certainly be aware of the dangers evolved with working with electricity! As the OP already quoted, electricity comes pretty close to magic: you can't hear/smell/see it, but it can kill you quite easily.
My grandmother lived on a very remote and isolated island in Norway. When they first got electricity, they had one lightbulb connection hanging from the ceiling in the best living-room (it was only used when having fine visitors). The thing was that when the electrician first lay out the cables, they had no bulb to put in the socket. Also the electricity was not yet connected to the house but would be soon. So each night they put a bucket under the empty socket just in case the electricity would be connected while they was sleeping. Not to spill anything on the floor.
Nice story
Lol that's amazing.
Wow
A colleague's grandparents, living on farm land in Belgium, would dress up on Sunday to watch television, thinking the presentator was actually talking to them and did see them.
I have a friend who turns off the switches on all his unused power points - not because of safety, even though that's sensible - but because he believes electricity pours out when there's nothing plugged in, wasting his money.
Derek is somewhat right about the time being roughly 1m/c for the bulb to light up but only because the parameters of the problem were picked to be tricky (sometimes fun and educative). Unfortunately Derek doesn't go into details in the video and only says that the bulb "won't receive the entire voltage of the battery immediately". This may mislead you into thinking that the signal speed in an electric circuit depends not on the length of wires but on the air distance to the switch, which is wrong. The signal speed in wires is roughly 50-95% of the speed of light and most often is what dictates how long it takes for something to turn on in most circuits. This is why, for example, matching copper trace lengths in PCBs is often important. Or why high frequency trading companies care about their internet cable lengths. HOWEVER, often in circuits there's significant wireless EM radiation, intentional (radio, wifi, microwave) or unintentional (reduced with EM shielding). Turns out that in Derek's circuit one side of the wire initially acts roughly like an antenna while the other acts like a receiver and the power transmitted could be enough to light up an LED bulb. At 100m it wouldn't.
This is the exact reasoning I was looking for. Thank you!
Your answer (1m/c seconds) is correct. The video answer D: (1/c seconds) is nonsense, because 1/c has the units of seconds/meter, not seconds.
thank you
Are you talking about inrush?
I share this sentiment. The EM influence at 1 meter takes 1/c seconds. But unless one has a clever inductive power transfer, not likely to light up the bulb. I tried to do the experiment today in the lab with 30 m of wire to make a video but the problem in the real world is dealing with inductance of long wires---but that said, I could kinda measure a 200 ns delay so at 100 ft, 50% the speed of c, that delay is right on par with what one would expect if the power has to traverse the length of the wire. A wire has the ability to contain the EM fields along the wire path and thus transfer power efficiently. However, with all this talk of wireless charging and some MIT breakthroughs, I can see this as a segue to that topic.
I am a third year Physics uni student and I can onfindently say that you have managed to explain the poynting vector better than any of my professors ever have...
I bet
That’s because I bet none of them have ever taken any education classes (not required if you can believe that).
Isn't that the truth. And also after working in the field for many years. I learned so much more on the job. Hardly anything I learned in school whatsoever.. barely. Just the basics.
Bro you need to watch some Eric Dollard lectures... I would recommend "History and Theory of Electricity" and "Origins of Energy Synthesis" right here on TH-cam if you really want to get at understanding the essence of electrical phenomena.
Just remember that a Theory of Everything has grave implications for Aerospace and Weapons development, and thus has major national security implications should it ever be out there for all the world to see, and thus why for the most part, we are kept in the dark as a member of the general public on topics that get deep into the essence of the reality of nature and natural philosophy!
@@Defooriginal he misspelled confidently....so you're just as wrong? 😆
You are the real teacher❤❤❤❤❤❤❤ Thank you and goodness
This was a GREAT explanation of circuits and electromagnetic energy. The one thing that could be talked about is that if any arbitrarily small current can turn on the bulb, then the long wires used to completed the circuit are not actually necessary--you could just use an antenna--and in this light the explanation is already common knowledge. It would have helped to emphasize the role conductors in "shaping" the fields, and that they are absolutely necessary to deliver enough power to the bulb, which would not be receiving maximum power until the signal travelled all the way down the wire.
Yea the wire is just a waveguide. I think he wants to make it sound more counterintuitive on purpose to generate more discussion :P
I was thinking exactly this. The way he was describing it made it seem like the wires weren't necessary. That you could just "shoot a field" at the lightbulb. I honestly still don't quite understand what the actual process is.
An antenna does not supply current to disturb the electromagnetic field. An antenna receives light waves, and processed into a signal using current supplied to what ever appliance.
A Tesla coil however, can produce high enough voltage, that it disturbs the electromagnetic field very well and can excite the fields even in very insulative air, to power devices in it’s proximity.
Watch videos on people powering light bulbs (and many other things) from the air around a Tesla coil. This might be the “antenna” you were thinking of.
@@Grynjolf i guess this was exactly what tesla thought with his wireless electricity radio towers 😅
There is so much to electromagnetic Fields and the like to explain, that this video could not explain it perfectly as well.
The Experiment is kinda obfuscating the whole thing. A Lightbulb is commonly known to take a while to light up and to draw a bunch of current.
A small LED or something like that would have made that topic better understandable.
If you were to do that experiment in real Life, with a real Lightbulb, then you could certainly see the time it would take for the bulb to light up.
With a low power LED you would certainly not see the time it would take.
Both having conductors with 0 resistance, but otherwise normal electric behaviour.
This actually raises more questions than it answers.
yeah i think that was the intent of the video... classic youtuber ploy
Yeah. But it is so with all knowledge.
means there's more to learn
as always;)
it SOO DOES!
naah everything is solved.
I have so many questions:
- If the energy moves through the fields, how does it light a bulb? What takes on the energy?
- People in the comments talk about shielding the bulb from EM fields. How does it work then? I need pictures.
- how do computers work, transistors, if it's not the current that moves the energy?
Give us more of this!
For the first question, the energy, after traveling through the electrical and magnetic fields from the circuit, will reach the bulb which has its own magnetic field around it. The energy will travel through that field and pass through the filament, thus lighting the bulb
The point being made is that the long wires back and forth will function like an antenna, and so the switching on will create a wave that is propagated over the distance between the antennas. The bulb will sense this (arguably quite weak) wave and flicker on. As an engineer I find this experiment a little frivolous, I think it will confuse people more than it educates people
@@jemert96 Exactly. You can see it as a two transmission lines or antenna. And it's unrealisitic long wires. I find the presentation kinda dishonest either way.
@@jemert96 Great point, thank you.
@@jemert96 It is also worth mentioning, that let's say two 300km straight wires with 1 m gap that aren't actually connected will for 1 ms (thinking about it, likely 2ms, but not so sure about that) act exactly the same as the 1c long cable. And the "not whole current" after the 1/c will be so minuscule, that nothing will actually happen.
I've always loved watching your videos. Ever since I was a kid, I've always wanted to be an electrician. After watching this super informative video. Im proud and happy to say that I am still not an electrician, and I will never be :)
Another important thing worth clarifying is that prior to the switch being closed, we have to assume that the system is in a steady state with a buildup of opposite charges on either terminal of the switch (if it wasn't in a steady state, then the light would already be on). When the switch is closed, current starts flowing (which sets up the magnetic field and radiates energy as discussed in the video), but it starts flowing at the switch and not at the battery. The battery doesn't "know" that the switch has been closed until the Poynting vectors from the switch reach the battery. So it's really the distance between the switch and the bulb that determines when the bulb first experiences any current, and not the distance between the battery and the bulb.
Yeah you are absolutely right
Yeah this is a huge piece of the puzzle. The "event" in this case is the switch flipping, so for causality purposes it's the switch-to-bulb distance that matters.
Is this true cuz that’s makes so much since. Or is it like what he said in the video the energy is going from the battery to the lightbulb directly through the air? What would be the case if the light bulb was intact 1/2 light year away but the switch stayed close. Alternatively what if the switch was 1/2 light year away?
@@TraxxasJr causality alone should make it a 1/2 year delay at the shortest in that case.
That makes more sense to me. I figured there would be a buildup of charge at the switch, and that the system could be simplified to electron source -> bulb -> switch -> electron sink, and it didn't matter that the source and the sink were at the same point. Only the fact that the bulb and switch were close together mattered.
It led to another thought experiment: what if there were two switches at the battery terminals that turned on simultaneously? To me, it made more sense that the electric field would need to propagate along the path of the cables, and only once it reaches the bulb (halfway) do electrons actually begin to flow along the electric field, creating the magnetic field. There is no Pointing vector without the magnetic field, and thus energy cannot flow until that electric field has fully propagated along the entire 2 light-second path (though it propagates from both ends, so it would take 1 second).
EDIT: Then again, what happens when the battery is a light-second away from the switch-bulb combo? Close the switch and the bulb is close, yes, but the battery has to somehow send energy 1 light-second away to the bulb. Would the energy have to travel for that full second? Or is there already energy that's "stored" in the existing, nearly-complete field?
I think one of the most difficult things about the Poynting vector is to visualise the cross product in your mind. That video with all fields represented in space is extremely helpful and should be shown in EM courses.
The poynting vector visualization is wrong though! Vectors are much closer to the wires. Unfortunately a misconception in this video
@@marvinalbert not wrong, just not 100% to scale is what you meant.
@@isaacgroen3692 Actually arrow directions are pretty wrong, they're much more parallel to the wires.
The vector isn’t a real thing, it’s just a mathematical device.
Once again I remember why I nearly failed E&M in college.
I see many engineers talking, and as non-engineer, I got more confused
Hope you can do a follow-up video! Some questions I hope I can learn more about:
1. The video seems to suggest that to transfer energy, just setting up a simple wire to set up the electrical field is sufficient. So how does resistance, voltage and the entire electrical engineering degree come into the picture?
2. With so many wires around the world, do these energy fields interfere / cancel each other?
I might have some misconceptions, so do advise!
1. this video ignores the *amount* of energy transferred in this way. It's true that some amount of energy always takes a straight-line path, but in real circuits, at steady state, almost all the energy is concentrated around the conductors (though still extending outside them to a measurable extent).
2. Yes, technically, every conductor that isn't perfectly shielded (which is of course impossible in reality) is an antenna, and both receives and transmits energy. In practice, we minimize unwanted signal transmission through shielding and just lump everything except the particular signal we care about into "electromagnetic background noise/interference", (which you can hear as literal noise with an AM radio) and try to make sure that the signal we do care about is many times stronger than any we don't care about. It's also possible to do signal processing to filter signals by frequency, making it easier to ignore background noise.
1. Resistance will cause the electric field to turn at a slight angle, opposite of that of electron flow. The energy flow vector will end up having a slightly inward angle, sending some of that energy into the wire (which ends up heating up the wire).
2. Yes, wires do interfere with each other regularly. Interference from wires is one of the major causes of internet connection unreliability for many people. The fields almost never cancel out though, because the electromagnetic field strength weakens rapidly with increasing distance from the wires. By the time you're a meter away, it mostly just introduces noise, rather than anything serious.
Basic answer - Electromagnetic energy propagates outward, in all directions, from the battery and the wires. Electromagnetic energy also travels infinitely far, but at insanely-reduced energy, as the energy inversely related to distance. So yes, all of the wires in the world do technically interfere with each other, but because of shielding and their distances apart, the interference is completely negligible. And yes, you could use just wires with no closed loop, but the energy would only be a short burst when you flip the switch. And don't forget, this entire concept is also based on zero resistance in the wire. In the real world, you would never have enough current to even "see" the bulb light up. You would need insanely high voltage to pass it through 300,000,000km of wire.
@casper . Isn't it crazy our whole life is based on things literally like magic and we act like its normal?
Oh so this cable transfers energy - whatever it just works. Oh this LAN cabel transfers literally billions of bits every second? Okay nice it works. I even learned how the LAN cable looks inside but it doesn't help - it's still basically magic but as long as it works. Only one human has to understand tech to bring it to 8 billion people.
Would the light bulb turn on if the cable was cut? Would it stay on if the cable was cut? How fast does the information about the cut travel?
2 questions:
1) Why does the light bulb have to be connected still? If I put a second bulb near the first one without connecting it to the circuit, why doesn't it also "catch" some of the energy and light up? (In particular in AC so the electrons already inside the bulb can be "reused")
2) What happens if a second bulb is added suddenly to an edge of the long circuit?
If I understood it correctly, for the energy transfer to happen you need both electric field and magnetic field, when you connect the wires, the electric charge propagates and you've got electric field then because of that the electrons start moving and you've got magnetic field.
I would say "the energy uses both fields to travel"
Yes! Would love to know this too!
@@SukSukulent You would be correct in assuming so. Also, air by itself isn't an incredibly efficient conductor. But the principle works, since we now have wireless charging stations, where you don't have to connect your phone or devices to a cable for them to charge. If electricity had moved through wires like most people think, that wouldn't be possible
1) You are correct, in the instant the switch is flipped, the bulb will receive some energy regardless of whether it is connected or not.
2) It will turn on some time later, when the propagating fields reach it
Excellent question. I'll be waiting for a proper response.
This is an issue I really need to think about, I'm a very good, now retired mechanical/electrical diagnostic & repair technician but I just accepted "electrons vibrate power flows in line" explanation and went to work. I've a always wanted to get back to this eventually. It's been 50yrs and eventually is here. Thanks for your great explanation, it's fantastic and very thought provoking!
Yeah, I'm a low level tech but do high end electronics including power conditioners. My first reaction was to wonder if Ohm's Law is valid, assuming this is. I can't agree or disagree. Interesting, to say the least.
@@rickmilam413 Great point, I didn't even think about Ohm's law but I can still see how it applies. The atoms and electrons still move, vibrate and get stretched a small amount while remaining in their overall place and they vibrate faster with increased voltage pressure, so the resistance would increase. That makes sense to me anyway!
I was taught electron flow theory. Each electron jumping to "hole" along an infintessimal string. That was 30 years ago.
Existence of proton and electron along a timeline. So neutrons seem to attract all particles.
I wish I still had a copy of Francis Bitters book. "Magnets" the education of a Physicist.
Works in progress to study celestial objects and their flux lines.
I can barely scratch build a low
power am/medium wave radio,
So I am no authority on electrical theory.
Earth has an iron core. So I maybe incorrect in opinion that electrons always seek the easiest path to earth ground. Free electrons being confined in the earths magnetic lines of flux. Lightning discharging in reaction to corona activity of our sun. Lightning is emitting somewhere on earth as manifeststion of lines of flux altering as our planet continues orbit around Sol.
Tesla chose Colorado for his wireless transmission station with a purpose in mind. Presence of conductive minerals underground. Ribbons of ores act as wires for electrical conduction. Some minerals being more conductive than others. 400 years of ore extraction by man has altered the static flow of seismic conductivity.
Tons of materials moved from below the earth to the surface. Changing the flow of electrons. Seismic disturbances ebb and flow and continue altering electron flow until
Unity lines of flux are restored. Polar flip is merely a tip of electron alignment of earths magnetic poles. Mineral fluidity under heat and pressure affect the magnetic lines of flux. Tesla could not finish his work to build another transmission tower south of the equator to prove his theory.
@@jasonb4703 The electrons don't actually leave the atom they are attached to, think of it like knocking over a domino in a line of domino's. You 'add energy to it by tapping it' so it falls over and bumps the one next to it transferring the extra energy, to the next to the next to the next and so on down the line but each domino remains in place. They don't actually travel from place to place along the wire or circuit!
This video is misleading. Just because the Poynting vector points in the direction of energy flow, it doesn't mean that it causes the energy flow. The conclusion is also dead wrong. Anyone working in a lab with a fast scope can observe the time it takes for a signal to flow down a wire. You don't need a stupid impossible single wire 2 light seconds long. All you need is a few feet of wire on a bench, and a signal generator with a fast pulse generator. Sync the scope from the generator, and probe along the wire. you will see that the pulse is delayed a bit more than 1 nano second per foot. Putting the end of the wire next to the signal generator doesn't make the time delay go towards zero.
By the way, for fast signals, the wire should be a transmission line, that consists of another return line spaced closely to the signal line, that is grounded. It could be a twin pair, or a twisted pair, or a coax with carefully crafted test points. The load should be a resistance equal to the characteristic impedance of the transmission line. Otherwise, you get the signal bouncing from the end of the line and traveling back to the generator.
At the end of a very intese physics course and right after the exams, our teacher ended it by telling us that everything we had just learned about the flow of energy in an electric system was most likely wrong and mentioned something about energy not passing through the cables.
Now I finally know what he meant. Thank you 😅🙇
What are the cables for then?
@@rocketpig1914 I might be wrong, but I think they are essentially allowing the magnetic field to form properly in the loop configuration and essentially becomes the structure the fields will form around. So for example, without the cable, you can't turn on a battery or switch and just power your devices, it needs a bridge to stabilize around and focus it's energy into. But maybe I am flat wrong, but this is how I am kinda understanding it
@@rocketpig1914 I believe they are to transmit those fields to your home, otherwise they'd disperse.
I'm actually dumbfolded by what I just learned.
I do remember thinking it was weird that a ring voltometer could work at all, If the coating of wires was a good enough insulator to protect me, why would a voltometer work at all? I won't pretend I've fully grasped the info in this video, but it does help me realize the importance of the field itself.
A teacher saying everything they just taught you was wrong is such a baller move, honestly. That's how you keep people curious.
Id guess that this is why an electric tester will sound in close vicinity of live wires. Great video. Thank you 🙏
Derek: Didn't rent a 2 light years long wire to settle a physics debate
Me: Disappointed, but not surprised
2 light seconds not light years
@@mrcat6433 well yes, but the original comment still remains technically correct. The best kind of correct.
Says the same dude
Please edit your comment
@@acrackedwall please comment your edit
"Now that you understand how electrical energy flows..."
Bold assumption, sir! I'm still wrapping my head around this lol
Yeah, I think I'm more confused now than before I watched this.
I worked with electronics successfully for years, and am severly confused now. I guess a working model is different from an actual model. I do want to see it accurately, because I'm of the opinion that you can do the best work and achieve the most that way. I'll keep reading and watching until I understand it I suppose.
I forget everything that I have learned in classes.
And considering the comments on this video; no, not everyone understands it. :)
He talked about electromagnetic energy, electrical energy still flows through the wire, but you can still use the poynting vector there to see the flow of energy because the current in the wires generate magnetic fields.
I've said it many times and I said it now. I'm a nuclear engineer, and the functioning of a nuclear reactor is pretty clear and understandable for me ... Now, how does the electricity generated arrives to your home : MAGIC. It cannot be otherwise
once it gets up to radio frequencies it ceases to be magic and becomes voodoo.
I second that motion. I have a mechanical engineering degree. Why do they have to obfuscate the truth with wrong answers??? First they tell you electrons aren't really going in this direction, they actually move in the opposite direction. Then they say PSYCH the electrons aren't really flowing at all! Then they do some hand wavy right hand rule black magic and boom, electricty.
@@KX36 and then there were microwaves and things really got hot
I still say magnets are the closest thing to real magic that exists on earth.
@@KX36 I like your comment. That's a great way to put it.
Thanks!
Question about your question! Are we assuming the speed of light is equal in all directions?
Smart
Lol
Won't change the results of the experiment though. At least if you measure anything 😋
Good one!
Good one dude
I have a question: Let's say the far end of that 300,000km wire was cut, then the light bulb wouldn't turn on, so in 1/c seconds I would learn that a cable that is half a light second away from me is cut. Doesn't this violate the idea that information can only travel at the speed of light?
This is an excellent question. Also wondering this.
Even of the wires were cut it would still receive some energy when the one half of the circuit gets energized. That's how antennas work.
Technically in this scenario you would only know that the cable is cut somewhere, but yes, I have the same basic question, and others too
I'd assume that the segment of the wire that you're observing still has a charge, but Idk anything. Really I'm just commenting to get notified when someone who actually knows answers your question
what a thought experiment. lets call elon and ask him to spool a wire behind his next spacex launch to test this
Holy crap. I have degrees in engineering, have investigated numerous electrical fires and worked for decades developing electro-mechanical devices, and no Electrical Engineer has ever explained electricity this way. Things now make a lot more sense.
His explanations are trivial, and answer to light bulb problem is absolutely wrong.
@leonidfro8302 source: "trust me bro"
@@leonidfro8302nah its correct and you just dont understand at all
@@variamente6855 The question is asked in highly misleading manner. There's no "misconception", Maxwell equations are known and taught in 2nd semester of engineering degree.
@@leonidfro8302just because they're taught clearly doesn't mean their implications are understood. As you're evidence of. Most people in these comments have studied engineering, as have I. Over a decade ago.
I’ve watched this video all the way through multiple times and even though I’m paying attention each time I am going to end up watching this again multiple times and still may never learn anything but each time I feel at least a little smarter🎉
"What you were taught about electricity is wrong"
Me (an electrical engineer): "I sure hope not"
Same, except as an electronic engineer lol
Lol same
What he ment to say is that what 99% of the population was taught about electricity is wrong.
I found myself saying; "that is very interesting. My knowledge of power plants and electrical fields generated within power plants leads me to believe that this is more likely true and I wouldn't disagree with the conclusion."
Damm that degree
Everyone's stuck on information traveling faster than the speed of light, but it doesn't..
It's traveling 1 meter in 1/c seconds. It just doesn't take the path we've always been taught in primary school..
Hello Derek, a physics professor here. I love your videos and I subscribe to your channel - in all honestly, I consider it the best example of public communication of physics and science I have ever met - I am not exaggerating. I actually used some of your videos when teaching to my students. However, you did not convince me with this one - not that I love you any less for this. I have similar objections to some that have been made by others here. The explanations of the fields, and the Poynting vector are gorgeous and very instructive, by the way. But I have tried to explicitly calculate the flux of the Poynting vector on the bulb, and I find it to be quantitatively a small effect (quickly dropping with distance of the bulb). Yes, there is *some* disturbance at the bulb, but I think it is a bit misleading to just say that it "turns on". I suggest to have this checked by other people - I would be very curious to see a follow-up on this. You are actually tempting me to try this out in my own lab.
Anyway, even if it turned out you had slipped on this one, that does not change my opinion about your work. Physics is non-trivial, and what really matters is to have the right scientific approach to problems, not to never ever make a mistake (even Galileo did) - eventually things sort themselves out if you follow the right track.
I would really appreciate if you try it in your lab.
I agree that physics is non-trivial and that anybody can make a mistake. But I'm a little disappointed by the lack of experiment. The thought experiment is a good idea, but a real experiment can show that you are right or wrong, and that is extremely important in the scientific method.
PS: to be clear, the reason for the effect not being immediately "complete" is that, although the energy does propagate through the fields and not the wires, the fields do not reach their final configuration until the other wire also settles in the final configuration, that happens only after several back-and-forth along the long wires.
One variant to this problem is move the switch to the other wire, next to the light bulb - what do you think would happen in that case ?
Yes I also think Derek has made a misconception.
When the DC current flow is stationary many seconds after switch is closed, then the magnetic fields of the long folded wires cancel themselves out because of the symmetric current. There is no statc field either on the outer wires since they are on the same voltage potential and the resistance is defined 0. So In the end there is a resulting energy flow actually over the short distance battery to bulb. So far so good.
But as long as we have a switching event, the fields need to establish, and this takes time with the speed of light. When switching on, the voltage potential change on the wire end triggers a wave traveling along for one second until it reaches the bulb. However I am wondering if this argumentation can still be done while assuming the impedance, thus capacitance and inductance of the wires to be 0. I feel this is contradicting and at least a non-zero inductance is needed.
I love to see comments like this.
Healthy discussion about science. Awesome stuff
As an electrician, a very curious one who always has to dig deeper into the why and hows of life. Im aware of the concept. Ive never met another electrician that understands or believed me. Great video.
Well, not to say that you’re wrong, but I too have thought this and I’ve been an electrician (now retired!) that thought I was the only one of us to believe it. Where’s Nikola Tesla when we need him???
are you hiring?
Hey, I'm about to start my apprenticeship as an electrician!
@@WyrGuy2 i didn’t say they didn’t exist, i just stated i hadn’t met any of them. Now i can say that i have. Nice to meet you. Tesla was a crackpot… an absolutely brilliant mind that i feel had more discoveries left to share with the world.
@@null-00000 i think its an amazing career. I wish i had started right out of highschool
As an Electric Engieneer(since a year or so), it seems my university never bothered to update on these topics, i learned about electric and magnetic fields as separate topics, and in some of the first and more basic courses about electrons moving throught the surface of cables. So its nice to see a video going deeper on this. Oh and just a little comment, electricity doesnt move at the speed of light on a cable, its better to call it "at the speed of electromagnetic waves throught a medium", and that material will affect to some degree the speed of propagation. Edit: or wait, is this tied to the incorrect explanation? since the fields travel through the air instead?
I am a Master Electrician for 30 years and we more or less where taught power was sent the tough the "skin" of a wire. Fact is many terms used are made simple so people can grasp it in real life situations. Wires clearly have a magnetic field around them or am amp probe would not work. Also working with high voltage cable there are bleeders around the cable like coax cable to discharge stray voltage or with cable wire shield it from stray voltage. I have a collection of old electrical code and theory books back to 1897 that hint at forces they did not really understand but they were spot on in almost all theory even in 1897. The books were made simple to explain wires like plumbing pipes, size vs pressure and this was good enough to have a practical understanding to size wires correct. I see this a lot like gravity when it is calculated as a force that pulls or attracts mass. That is not how it works but the math is correct even if the understanding is dead wrong. Mass bends the grid of space so objects are traveling straight on the grid but the grid is distorted.
Poynting derived his stuff in 1884. But it is largely irrelevant for circuit theory or even for transmission line theory on which the bulk of even very advanced electrical and electronic engineering is based. This video does not portray this truthfully.
I loved this video, and I agree, when it comes to educating people for practical real life scenarios, sometimes it makes more sense to give approximations that work well practically. But I guess the crazy part is that the teach it that way too even theoretically.
What are the titles of these early books? I've found old textbooks present information much clearer than modern ones, so I collect them too.
Correction: Gravity bends the grid of spacetime.
The video is theoretically not incorrect, but very misleading and I think a bit sensationalized to draw likes. Thank God physics professors don't wire up our homes!
I'm an electrician; not the sort that you call for installation or problems at your home, but the sort that does industry support (automation, controls, low voltage service, etc). I love the conversations that arise when someone comes around with seemingly random knowledge that is applicable to our work in ways not often considered.
Without fail, everyone starts off with the, "mmhmm, sure buddy" look. Then something clicks and suddenly they realize that voltage output in our 3 phase motor drives is proportional to frequency. Cranking that output up to 100Hz to get more speed causing failures is starting to make sense. Then everyone is full of questions. A group of middle to late aged blue collar folks clustered together in a dozen different excited discussions. It's a beautiful thing, that I'd wager isn't often witnessed outside of enthusiastic classrooms. Easily among my favorite experiences.
I bet this one will lead to something interesting next time we find a disconnected shield in some com cable.
mmhmm, sure buddy
I'm an electrical engineer too and I can't agree with the video because of the 100m ethernet cable limit. If you need to route ethernet to a terminal across a factory floor, you might be forced to loop the cable into the ceiling ducts due to safety regulations of obstructions. If the ethernet cable length exceeds 100m, even if the terminal is merely meters away on the other side of a wall, you are out of luck. However, if Vertisium's conclusion that the bulb lights in 1/c holds, then delay is limited by Euclidean distance and not cable length, and I'd be able to make the connection even if I used extremely long cables. This is clearly not the case.
Meanwhile we once had a new young electrician asked to connect some wires to be used for some angle grinders. The bosch exploded, then the dewalt. The kid sent 3 phase current instead of taking just one phase and ground as neutral (probably not code but it works in a pinch, im not an electrician btw)
@@wwmmxd Ethernet does more than simply deliver power.
At last!! I had a high school teacher 54 years ago (Dr. Schoenfeld) that beat your electrical pressure/EM field transfer of 'electricity' through a circuit in our heads. Later, I recall on a test in college Physics 110 where the correct (or accepted) answer was always ' ...by virtue of the flow of electrons through a conductor'. I always wondered how many of us students took a fraction of a loss in our GPA due to this belief. Excellent video explaining how capacitance (or inductance) play a role in something most everyone takes for granted. More I²R to you!
Theoretical vs Practical! Which direction does your battery flow?
I'm still not sold on this idea. The Poynting vector is a just a representation, and not meant to be taken literally. It's like velocity. Velocity has a vector that can take several small components and make a larger vector using vector algebra. Same with the Poynting. The power transfers by several small jumps that contribute to the overall sum vector. The case of the undersea cable doesn't prove anything about power transfer as a whole vector- it only proves that electric fields transfer better with an insulator as in coaxial lines.
I just want to point out that in your setup, (battery, wires, switch, lightbulb) there can be no impedance, because your power source is direct current, not alternating current. (I know small irrelevant detail. It matters to me, because as a newly licensed HAM, I've been studying RF quite a bit lately.)
I have studied electrical engineering for four years. I finally understood why we as an engineer sometimes needs to approach a problem in scientist way. We are just applying some formulas without digging deeper to the profound concept of understanding.
Yeah the electronics engineering courses I took gave Maxwell's equations the same cursory treatment. It annoyed me so much that we only covered the 4 commonly cited ones while there are actually more to his work.
It's astonishing to me that people can use math to engineer (successfully) without understanding the core physical reality of how it works.
There are aggregates of inprinted sheets of papers glued together we call "books",
you can purchase this kind of stuff or borrow them in various places on this planet.
generally they come in different sizes and contain informations on the subject of your choice.
you will be surprised, if you read some early electric motor sheet paper aggreagate, to find out that there was not a single innovation in this domain in 100 years, and all of the discoveries on this topic were made by one dude named N̶i̶k̶o̶l̶a̶ ̶T̶e̶s̶l̶a̶ Elon Musk.
@@josh__mclendon that's how engineering is taught unfortunately.
In electrical engineering, power system for long transmission line, voltage and current are assumed to be traveling as an electromagnetic wave, but never knew time for transmission depending upon the vector displacement between source and load.
A fraction of the energy passes through the fields directly between the source and load, and another (larger) fraction passes through the fields near the wire. So in the idealized case discussed in the video, a small amount of energy passes through the air, and that's enough to light the bulb. For most realistic circuits with relatively short and widely spaced conductors, the amount of energy passing through regions of space distant from the wire is pretty much negligible, particularly since most realistic systems have a minimum voltage/current at which they'll activate. The answer in the video is only correct under the assumption that ANY non-zero current is sufficient to light the bulb.
If the bulb in the video required a minimum voltage across it that was some fraction of the battery voltage, then it wouldn't light until a sufficient fraction of the energy from the battery arrived at the bulb. Most of the energy travels very close to the wire, but there are also paths directly from battery to lightbulb, as well as paths that follow near the wire partway and come back near the returning wire. So the voltage seen by the bulb will gradually increase as energy along each of these paths reaches the bulb, with the full voltage only showing up when the fields travelling very near the surface of the wire arrive (~1 second in the setup in the video where the wires are one light-second long from source to bulb).
Yes ! Such an hypothesized light bulb would just light-up anytime you get it near a cable with AC going through it... This is an abusive hypothesis.
Yes, Veritassium is wrong in this case.
So you are saying that if I took a magnifying glass and drew dense field lines very very close to the wire most of the energy travels through that all the way?
Yes, exactly! Veritasium essentially just showed as that a nano-Watt of power will radiate instantaneously as if the light bulb is the receiving antenna of a radio. Totally not what his question was framed as asking!
I completely agree with you, I feel like the question is misleading and the "correct" answer is only valid for a very small distance between the source and bulb. The wires still serve a waveguiding function and the vast majority of the energy propagates along them.
With such a long wire, how do the fields "know" where to go? How is it able to transmit energy immediately, but a disconnected lightbulb another meter away wouldn't power on? (or maybe it would?) In fact, how does current "know" to start flowing when the circuit is complete?
Or what would happen if you cut the wire at one of the tips? Would the field instantly start receeding everywhere? 1/c seconds to turn off?
Exactly this. I need answers.
That's the best question.
You need a conductor to propagate the EM-field.
I think it would still turn on because we effectively have two antennas, one at the battery and one at the bulb.
Yeah, I think he's wrong on that one. With no wire to guide the waves, the light bulb wouldn't feel the source.
If you want a more detailed simulation see the video I posted after he posed the question the other day. I can simulate your alternate scenario as well if you'd like!
This has been amazingly helpful. I cannot learn the way my education teaches. I know they try to simplify things down for children to understand, but if I can't clearly picture how something works it doesn't stick in my brain. I need the greater depth for it to make sense. The information they taught in school always contradicted what I learned outside, and that lead to endless confusion. Electricity therefore became a point of endless procrastination because I was just so damn frustrated with it.
Like a lot of comments on here, there is a big problem I saw:
You’re severely undermining the importance of the cable. Yes, the magnetic field carried the energy for the bulb to light up. But the field is strongest right at the wiring. The instantaneous power going to the bulb is a very small fraction of the field. The wire acts not only as the way for electrons to flow, but also for low impedance transmission. The transmission through air is much, much smaller than transmission following the wire.
EDIT: Veritasium's new video clears up the major hole that this video brought up. His visual representation of the circuit in the original video was the major issue. The point I made still stands with that representation (insulated cables, car battery, lightbulb). I'm glad he refined this.
That is exactly what I thought after watching the video. The power transmitted through the EM field has the highest flux inside the wire due to metal's high permeability. If the power could as easily travel through air as through metal, we wouldn't use wires to transmit energy/signal in the first place.This is correct that the light bulb in the experiment would light up after 1/c s, but it would be initially very dim, and gradually increasing in brightness until after 1s, when the EM fields traveling through the wires catch up.
Didn't tesla come up with a death ray because he thought that we could transmit energy through the air effectively?
@@mateusz7590 Uhm...he did say exactly the same thing in the video, tho. I think people are just pointing out at simplifications made for divulgative purposes.
These "thought experiments" are never meant to be broken down, otherwise you will always find mistakes. They are obviously wrong, that's the whole point, otherwise we can continue adding an arbitrary number of real considerations and debate whether my personal choice of considerations are more accurate than yours. In reality none are, they are just meant to more easily represent a specific phenomenon, such as the fact that energy can in fact travel through air, which was the point of this video.
@@mateusz7590
Yes, there will not be enough energy transferred to the bulb until the waves have traveled sufficient distance down the wires to induce enough current at the bulb--even over one meter there is going to be quite a drop in power. He seems to imply that the energy jumps from the battery to the bulb with sufficient power to light the bulb--answer was D.
This is basically transmission line theory (I'm an electrical engineer who specializes in this, in electro-magnetics). You can view the two lines connected to the battery as a dipole antenna, same for the lines connected to the lamp, and that the two antenna's are shorted at the ends to one another. These antenna's operate in near-field. Another way of looking at it in this particular case is that a capacitor is formed between the lines connected to the battery and the ones connected to the light-bulb. I do not agree however, that the circuit behaves as you said it would, the power transferred should be in the order of milli- or micro watts which is not large enough to cause the lightbulb to glow visibly as it would require tens of watts, you should put it into an electromagnetic simulator to calculate the exact power transfer.
The "light bulb" is really an idealized current detector which consumes no energy from the system. Thus, even if just a nanowatt is transmitted to it, the "light bulb" comes on instantaneously at detectable brightness. Obviously real electric light sources do not behave this way, but this is a thought experiment.
Thank you for this explanation, I was totally lost on his explanation until you mentioned that these lines are acting as (near field) antennas. Otherwise I was lost in the weeds trying to figure out how you could shortcut a transmission line's delay.
I'd like to see more explaination about the antenna/near-field thing, I think that's missing in the video. Together with a diagram of a more complex, less geometric ideal, power transmission.
@@killerbee.13 Random noise sources want to have a word with this thought experiment
You will need time that enought to energy transmitted by resistanceless antenas of certain lenght to light a bulb. So you will need (x+1)/c or 1 which is smaller, seconds there the x is length of antenas required to generate power to light the bulb. Possibly it will be already shine if x is smaller than c/4.
This is exactly what i love and adore about physics: even the most fundamental concepts are so hard to comprehend, so that during the first few years of education we are told the most comprehensible "lies" in order to ignite the fire of curiosity and begin the search for what's really going on - fascinated by the mechanisms of the entire cosmos along the way. The ultimate way of teaching anyone to question, observe, experiment and evaluate. Great topic and really on-the-point video.
I was put off by the lies. I'm quite angry about it to be honest. Children are smart enough to understand this, we should teach them from an early age.
Gonna tell my teacher she should stop teaching f=ma until we find a theory of quantum gravity.
@@peepiepo agreed. I was a curious kid and learned a lot outside class. Learning old or bad information broke my brain especially when I would ask the teacher and show them I was right.
@@peepiepo I'm sorry if i put it wrong but i certainly did not mean we are being lied to while learning these concepts but rather encouraged to be sceptic about them so that we would find the truth - because they are not entirely understood by someone teaching/explaining to us - as being the building blocks of scientific understanding.
Just like in Atomic theory. Children are taught that nucleus is like the Sun and electrons are like planets, while in reality, these particles exist as probability wave functions.
I remember day 1 of EE being like, "so we're going to learn how to do circuits over the next couple of semesters and when you take EM fields you'll learn why all of circuits is kinda wrong." Turns out he wasn't just messing with us.
I wonder how it would look if all circuits education was redone with the field lines in the diagrams and explained that way...
If I remember correctly, as long as they’re relatively low frequency circuits, circuit diagrams work just fine
Are you suggesting that there might be a different way of looking at developing whatever it is circuits do? E.g. there might be different ways of directing energy field lines?
Circuits are not WRONG and they obviously work. But they are working at low frequencies where good old Kirchoff's Laws work fine. At radio frequencies and above other factors start to dominate.
@@thomasmaughan4798 yes since the frequency is low, the reactance due to parasitic inductance and capacitance is negligible
It's great to see the Poynting flow argument reaching such a large audience! I always cover this in my college E&M classes. But I have to say that the claim that the light bulb turns on right away is pretty misleading. Consider the case where the circuit is actually open -- somebody cut the wire 300km away. By causality, the light bulb's behavior is identical in both cases (closed and open circuit) for t
Yeah, this video is really misleading in the way it presents the flow of energy through fields as a result of varying voltage as the main way that energy is transferred through the circuit. Not to mention that the "electrons move really slow" things needed to be elaborated on, in both DC and AC it is a chain reaction not too unlike a newton's cradle that moves the electrons further away and transfers the same potential (Voltage) to them.
The electrons carry the potential to do work and then as they flow they lose that potential and regain it as they pass through different systems. I feel like this channel has been focusing more on being shocking then actually properly explaining the subject matter.
@@CrystalLily1302 no, the pointing flux part is fine. The em fields definitely carry the energy. The problem is with the idea that the light bulb "turns on". Just a language issue, not a physics issue
@@CrystalLily1302 agreed
@@SamGralla it IS a physics issue. the energy the light bulb gets after "1/c s" (whatever that is... it's a meaningless quantity and hurts my eyes as a physicist and teacher) is way lower than what it gets after some seconds (not just 1). because the energy travels through the fields, but the fields are established by the current. and they travel as a wave (slower than c!!!) along the wire when it is switched on.
to really let the bulb glow that fast he would have to use an incredible high voltage battery.
Adding onto this, the Poynting vectors shown in the illustration are the steady-state vector field. They do not reflect the reality of the EM field during the transient period as the circuit reacts after the switch is closed, which is what needs to be considered to answer the question.
When one does consider the transient state, the result is that some small transient inductive currents do appear at the bulb, but the net power flow into the bulb remains essentially zero for the first second. Only after the change in voltage propagates from the newly-closed switch along the wire all the way to the bulb, do we finally see a persistent voltage drop across the bulb, which produces a steady current and hence a net power flow into the bulb.
Furthermore, even just looking at the Poynting vectors from the illustration, the vast majority of the power flows along paths very close to the wire. So if we consider the opposite question, “What happens when the switch is turned off after it has been on for a while?” we get the answer, “Energy is still flowing along Poynting vectors close to the wire for an entire second after the switch is turned off, and a small amount of extra power continues to follow even longer paths in the space beyond, so the light stays on for at least a second after the switch is turned off.”
Considering how long ago we learned to harness electricity and create electrical circuits and how much misconception surrounds it, makes me wonder about other things we've misunderstood yet utilized nonetheless.
Yeah its very interesting to think about. I wonder if there’s any math we use in common practice that’s not completely accurate and would therefor disprove scientific theories we’ve accepted as being true.
It is fascinating how often heuristics can be just as good, or sometimes even better, than actual absolute knowledge. "Rationality for Mortals" and "Antifragile" are two books that talk about that idea, more so the former, the later kind of hits it tangentially.
@@johnwiand1167 yea i know how ya feel, but we already know that all established math formula give no certain answers without some margin of error, even 1 + 1 = 2, whatever that 1 of something is that your adding is likely not going to have to same number of atoms as the other 1 of something your measuring therefore your answer must be a decimal value.
further, even electrons, protons, and neutrons have mass that can be calculated to some approximation but impossible to measure exactly which makes measuring anything exactly impossible.
Yes - a lecturer once told my class that we (humans) understand radio enough to make it work for us but 'exactly' how it works is still a mystery - to be fair that was 30 years ago!!!
Women?
I'm mildly confused... Provided that i tried using thw right hand rule in the "AC circuit" electric and magnetic field diagram he gave in 9:15... Did he not show the electric fields in the backwards direction around the battery and in the center region??... I mean... Whenever you apply the right hand rule around the source... You don't get the correct vector... For electric field downwards, the magnetic field should be into the page to get the required resultant vector.... As in the DC current demonstration he showed in 7:05 (for electric field being from positive to negative... Unlike the AC diagram he made) and 8:02 for the full diagram.... But around the AC source ... The arrows are backwards.. and even in the central region... Right??... I'm so confused on this..
Now that I've seen the same diagrams like 5 more times... In the AC diagram... He made the electric field lines from negative to positive.... Which has to be wrong... THERE'S JUST SOMETHING THAT EITHER I'M NOT UNDERSTANDING OR IS WRONG
@@AbbyHatcher-gd7bh Get your keyboard fixed.
The magnetic field is definitely there. Whenever I'm welding steel and the floor hasn't been swept in a while the steel filings align with my earth lead, which leaves some nice patterns!
That's not what's in debate. This is a given for a long time. It's the way the energy gets transmitted. Most think over electrons but we just have gotten it explained otherwise
@@flawnski No one said it was.
@@felixisme @flawn I'm neither debating or claiming anything ground breaking. It's just cool that it's a visible example of the phenomenon and I thought I'd mention it for those who may not typically come across it.
@@thomashenderson3901 everything cool, was just trying to uncover a possible misconception of yours 👍🏼
@@flawnski And that's cool. 👍🏻
"Now that you understand how electrical energy actually flows..."
I DON'T, DEREK, I DON'T!
Yeah, that's an oof on Derek's part. I was watching this and getting confused despite understanding the concepts.
Basically, you can think of the flow of electricity like a game of telephone or passing a baton. A generator starts by exciting electrons at point A and that energy propagates through the wire to point B. The electrons themselves don't go very far, but they don't need to, since each one is a carrier. As the energy flows, it generates heat due to resistance in the wire and a magnetic field around that wire, which spreads out like an "aura" around it. This "aura" can align other wires nearby to the same magnetic field and thus passes that same energy to them without the wires being directly connected. This is why live wires can be dangerous and disruptive if not properly insulated from one another.
This is also similar to how data can be transferred wirelessly via other kinds of waves like radio or other frequencies, but that's a different story.
@FlyingMonkies325 Yeah, I was just giving a very simplified overview about the concept in layman's terms. It has been a while since I've looked into the details, but point is, Derek went from debunking misconceptions right into Maxwell's equations. I can see why people would be confused with his explanation.
What a perfect name Poynting had so that his vector points in the direction of energy flow! Reminds me of how the Schwarzschild radius for a black hole was calculated by a physicist whose last name means "black shield" in German.
Right? When I first taught about the Poynting vector, I thought my professor had said "pointing vector", and he had to spell it out haha.
That way he wouldn't end up disappoynting us
Bruh i speak german and i never realized that
Nominative determinism
Yeah. I laughed at reading the name. It's like an unintentional pun.
I admire your work, even when I was teaching high school students 10/12 years ago, I used to show them your videos. Thanks @Veritasium.
I hope you have a good day. I hope you get everything you've ever wanted this day or tomorrow. Keep going, and don't let anything get in your way. I love you.
I realize this will get buried under 25,000 other comments, but I can't help but wonder about a possible relativity paradox.
Imagine that a person does create a circuit like Derek has suggested - a simple battery to light bulb circuit where the two arms of the circuit are an absurd length - but let's make each arm not 1/2 light second but a light year. Derek flips the switch and turns on the light. But...a person at the far end of circuit arm (1/2 light year away) wants to send a message back to Earth. If they momentarily interrupt the circuit from their great distance, wouldn't that turn off the light, and by Derek's explanation that would presumably be near instantaneous. This would seem to violate the principle that nothing - including information - can travel faster than light.
I'm *not* suggesting that this thought experiment proves Derek wrong. I'm just wondering about how to resolve the paradox.
The information that the circuit has been interrupted would not be instantaneous, what makes you assume that it would? Even when the light bulb is meters away from the voltage source it still is a nonzero time for the signal to be received. Fields still can only transport information at or below c.
Maybe simpler : the circuit is 1 light-year long AND we don't know if it is open or closed at the very far end (which is 1/4 year away). When I push the switch, how can the magnetic field know in 1/300.000 second if it can transmit power or not?
@@LeCheneDeTele In this case the 1 in the numerator is distance, in the video its 1 meter i.e the distance from the source to the lamp ,in your question the units are light-years. Converting this to meters you might feel a bit better. I wouldn't blindly trust my calculations, but just treating everything classically I believe it would take about 91 days in your case for the lamp to turn off or on.
@@KayaksAreBoats Then how does the bulb even "know" that the 1 ly long wire is an actual uninterrupted circut?
there is no paradox in the question as written.
I have a degree in Mech Engr and my Physics E&M class was the only class where I was like “yeah I just don’t get this”. Sometimes I’ll wonder though if it really was that bad. This video just reminded me that yes, yes it was that bad.
yess @clarierich my whole Electrical engineering is flushed today....
it's interesting to get this phenomenon....
please clear my some dough ...so i can better understand this.
so what we checked in ampere meter ....
what is the meaning of current raised ...
so how battery ..drain,
why conductors overheated ..when current raise..if electrons doesn't flows...
We keep the energy away from the conductor, it must not flow there, so we coat the conductor with isolation to keep the fkrs out@@lalitjoshi7152
I'm also an EE and I just got stumped. In a few minutes all my knowledge is getting jumbled up in my brain.
@@lalitjoshi7152 please clear my some dough ...so i can better understand this.
@@lalitjoshi7152 Current needs a complete circuit to flow, in a conventional circuit, it's basic Ohm's law. Open circuit = maximum voltage, zero current. Closed circuit = maximum current, zero voltage.
Negatively charged atoms (determined by electron surplus so we can say electrons instead) repel each other along the conductor in which they're present, this is why a thin wire cannot carry a large current - electron density. There's only so many electrons in a small space. In doing so it generates heat and yes, current flows. See my post below for where I believe this video gets it all wrong. The same electron as given by the battery is not the one that appears instantaneously to light the bulb.
You in line ammeter is measuring electron flow, just how you think.
Battery is drained by having free electrons removed, just how you think. It's energy was needed by the device in question to produce either heat or light or both.
Conductors overheat because of electron flow, just how you think.
Until I see good reason otherwise, I consider this video incorrect.
That's a great video about power transmission! I remember being surprised by that in the university.
I really don't like the 1/c answer, though. While it's technically true that there will be some voltage on the lightbulb after 1/c simply because the electromagnetic fields generated around the wire will reach it, but it has nothing to do with them being connected by wires. In the same way, you can say that turning on this battery will "turn on" every single lightbulb on the planet. This is also technically true, because there will be some field generated by the battery in the entire space, and it will induce some voltage everywhere. Although its value will be negligibly small, as the magnitude of fields around the wire quickly drop with the distance from it. Only after 1 second, the proper connection through the electromagnetic mode of the wire will be established.
If you replace the wire with an ideal coaxial cable (which doesn't let any EM fields outside the inner space between the two conductors), the answer will always be 1 second, as there's no leakage and thus no way for the lightbulb to receive the EM energy from outside the incoming cable.
Yes this video seems to have been deliberately constructed to be obtuse and misleading. Anyone with a decent understanding of induction can tell you some fllux gets to the bulb in 1/c, but there's an inherent assumption that the bulb needs some threshold of voltage to actually light, or by the same logic every bulb everywhere is always lit from background EMF
Great video on such a complex and controversial area of physics. It may cause people to argue that it is dangerous to be anywhere near the 'field' of wires or power source ( just like the controversy over living near 'phone masks!! LOL.
Yes thank you for saying this
The bulb being ordinary ruined him.
@Dalnore @Tim Sheehan, I agree but at 0:45, part of the assumptions he asked us to make is that the bulb will light up immediately as soon as current passes through it. The unfortunate demo of it lighting up that brightly is misleading but I’m not sure we would’ve noticed the difference in real time.
Makes perfect sense, but you’re just describing electro magnetic induction. I’ve never seen a short circuit from the magnetic field of an insulated conductor. Current still must have a path to ground to discharge energy, not through the magnetic field.
It's pretty easy to test this. Just take a 100m length of 50 Ohm coax cable arranged in a big loop with the ends 1m apart, connect a 50 Ohm pulse generator to one end and a 50 Ohm resistor across the other end. Use an oscilloscope with two matched probes to see how long it takes for the voltage to arrive at the resistor. If it makes you happier you can put an LED in series with the resistor and cal it a light bulb. The result will be about 0.5 microseconds and not 3 nanoseconds.
Of course I know I'm talking to myself, there's no way Veritasium can read 30,000 comments.
At least I just read your comment if it makes you feel better :)
Who loves ya baby?
@@petehiggins33 - we're all born bald
@@kojak8403 But some are born balder than others.
Why they do not take into account that the most of energy propagates along wires so it takes 1 s to light up the bulb at full power
1) Energy _is_ transferred by _em_ fields in the direction of the Poynting vector.
2) This can be considered to be energy transferred by photons.
3) Photons 'follow' many paths. In free space all paths are equally probable.
4) Photons interact with electrons in the conductor. When superposed there is an increased probability that these photons will 'follow' the path of the conductor.
5) There is a finite probability that some photons will traverse the path from source to sink by the direct route, taking a time (1 m / _c_ ms^-1) = (1/c) s.
6) It is more probable that photons will follow the path of the conductor. Such photons will take a time (L m / _v_ ms^-1) =(L/v) s, where _v_ is the velocity of light as affected by the electrons (left as an exercise for the reader), and _L_ is the conductor length from source to sink.
Conclusions:
Some energy _will_ reach the sink in (1/c) s, but the overwhelming amount of energy will take (L/v) s.
If the light bulb takes an infinitesimal amount of energy to switch on then it will do so in (1/c) s, but if it is a real light bulb it would have to wait for photons to follow the conductor. Probably.
But, as scientists do not decide by voting, has anybody carried out the experiment?
Good you mention photons. Tesla did all the experiments, yes only a very small fraction of the charge field (photons) reach the bulb, but also NO PHOTONS are stored in batteries, they are already all around us, the earth has a charge field, the photons come straight up out of the surface. The wires etc just give the field of photons a path they can take, ie go through the lightbulb wire, as photon density indreases, the atoms start to give off visible light photons as an atom/molecule can only recycle/process so much photons, the photons are spun up. The standard charge field photons are sub-infrared. To research anybody can read Miles Mathis.
@@danielarcher369 If the photons are being pulled from the Earth's EM field, how do electrical systems function on spacecrafts?
@@pleasejustletmebeanonymous6510 space is filled with charge too, it connects all stars/planets, galaxies, basically the whole universe.
@@danielarcher369 thanks
what im not getting is, why is copper needed, if electricity flows through magnet field?
Pease explain as if im a 3 year old. thank you so kindly
I love the comment section. People put arguments and ask great questions. Some even put interesting hypothetical cases related to this concept of energy flow. It makes the video even more interesting. It makes me realize that there are so many things about science that we haven’t even fully grasped on.
Since the death of only 4 terrestrial tv channels in which to choose in Britain- of which two offered scientific shows on a regular basis , a lot of very young peoples’ slight chance of science igniting their imagination has been diluted . Then again I hear how Video Gaming now encourages all kinds of conceptual things so I’ve just ruined my argument...Sorry for wasting your time 🙄👍
Remember though that while the comment section may not fully grasp it, the scientific community almost definitely has.
@@Xentillus maybe, but even in scientific community, ideas are always challenged through conferences and journals. So it begs you to question your current perspectives.
@@Chris-rg6nm The electromagnetic field must still propagate through the wires at the speed of light, otherwise this is FTL energy that violates causality.
Z
You should be an Instructor somewhere, if you are not already. Your demeanor & voice are top notch towards teaching!
I really like how you have started almost teasing us with the community posts and awesome follow up videos, please keep at it.
this is a bot.
One correction to this video: The four shown equations...Maxwell himself never saw them. Maxwell used the formalism of Quaternions and he always wrote 8-12 equations. So it was very difficult to read the stuff. It was Oliver Heaviside, an autodidact, who later reformulated Maxwell's nasty-looking equations by using Vector Analysis. With that fairly modern tool Heaviside also managed to compactify Maxwell's 8-12 equations into 4, and gave both integral and differential forms.
This led to the situation that since the 1890s the equations of electrodynamics were widely referred to as the Heaviside-Maxwell-Hertz equations. Around Einstein's era Heaviside's name was slowly dropped, unfortunately. Einstein himself always spoke of the Maxwell-Hertz equations. And later, Hertz's name was also dropped and all the name-fame went to Maxwell - not entirely deserved though from a scientific point of few.
True.
Maxwell developed the entire concept of an electromagnetic wave, but his mathematics was cringey. Using vector fields, line integrals and surface flux integrals, Heaviside improved on the concepts of divergence and curl operators, so achieving the four famous equations that are so easy to apply.
If you get inside the physics meaning of Maxwell equations, you can see there is no difference between the original equations and the versions improved upon by Heaviside, this is why his name has been dropped; the scientists of the time cared of who developed the concept.
But. The Heaviside version allow everybody to conduct calculations, without the necessity to get deep into a difficult field of our physics.
Quite so. I'm the historian of science Derek talked to a couple of times in the video; I lay out the whole story of Heaviside and his rewriting of "Maxwell's equations" (to which he was led by his independent discovery, not long after Poynting, of the energy-flow theorem) in my book "The Maxwellians." But I have to say that Heaviside himself was fine with calling his set of equations "Maxwell's"; he regarded them as just a distillation of Maxwell's theory.
@@bjhuntaustin I very much enjoyed your book! Heaviside was quite a character.
For historical reasons they are called maxwell's equations. Heck he wrote them all fairly explicitly in his book about it.
It's really disingenuous to say the bulb "turns on" in 1/c seconds. Yes, some energy does transfer in that amount of time, but the vast majority of energy transfer is in the EM fields around the conductors, not in the air gap between battery and bulb. This also completely ignores more nuanced effects like reflections due to impedence miss-matching or capacitive and inductive coupling.
You could have avoided most of these issues by simply including a plot of energy/time for the light bulb, which would show the bulk of the energy arriving when a lay person would "expect" it to (ignoring reflections), 1 second after turning on.
This is akin to saying "which way to gravity pull you?" and instead of saying the answer is down, or mutually up and down due to your mutual interaction with the earth, that instead gravity pulls you everywhere because everything in the universe is pulling on you simultaneously. Yes that's true, but it very much ignores the elephant in the room.
I'm afraid I'm actually not going to listen to this guy anymore. I prefer Sabine
Thank you. Thinking the same thing. I think his falls into the "spherical cow" argument and completely ignores reality since its basically assumed to be acting as a big antenna of sorts with mutual coupling in the conductor and not acting as a normal wire would if it were laid in a large circle and propagation velocity and all the other sundry topics like characteristic impedance and such come into play. Sleazy slight of hand IMO. Thanks for removing the dislike button, YT.
And now that I think of it, this is analogous to the issue that my older LED lights up in the ceiling of my last house had. As they did not have discharge resistors in the capacitive dropper supply, there was enough capacitive coupling in the switch and wires to make them glow dimly as there was sufficient voltage, but very little current available. I would say most people would not consider that to be "almost instantaneously." More like "on", but in a very annoying way.
Is 12:39 not the graph you're describing? - "You could have avoided most of these issues by simply including a plot of energy/time for the light bulb"
there is an energy/time graph in the video?
Ok, I think I've got it, if my assumption is correct:
1. The field needs to be established. This will take the 1s or 2s for the whole build up. The voltage is there then, but the current is not turned on, yet.
2. Then on releasing the current the energy will flow along the field, so only the distance battery and bulb matters.
Correct?
By initially physically connecting the Battery, first 1. happens, right? So 1 second.
Otherwise the build up wouldn't have known if someone near the moon would have cut the wire long ago.
Perhaps if you think of all electrical cabling systems as RADIOS that just happen to use really long antennas and you'll get a more intuitive idea of what's going on here. The energy is always transmitted via fields, but the wire acts as a much more efficient wave-guide, rather than just throwing the field outwards in all direction.
That's amazing! Thanks, made me understand it much better.
Thanks. Now it makes sense!
No, this analogy is incorrect, but I don’t blame you because, as an electrical engineer, I can assure you that this video is full of errors. Antennas transmit data very well, but they transmit energy very poorly. For instance a 1,000,000 watt AM broadcast tower will transmit data over 100 miles, but you can safely stand within 50ft with no adverse affects. If your body was subjected to a tiny portion of 1,000,000 watts you would die instantly. This video is fundamentally flawed because the EM waves that propagate radially directly from the source dissipate very quickly and have negligible energy by the time they reach the intended target. If this was not the case, the power source could light the bulb without requiring wires. It is the EM field generated along the wire that brings the power source to the destination and provides sufficient power to light the bulb. I wish he would peer review these things before going through the trouble of making a video that misleads people. All the best
That makes a whole lot of sense
@@SignalCorps1 oh, ok
Technically correct but misleading. Electrical Engineer's take: The EM waves will take 1/c seconds to travel the physical distance because it's not traveling through the wires. You will see some current at the other end. The current generated EM waves and they have physically propagated to reach the light bulb. The Poynting vector is useless in this case as the battery doesn't even know the light bulb exists yet. Basically a misdirection here.
This example is actually just two antennas initially before it comes a circuit. The current will be based on the inverse square law at the 1 meter distance. Since it's a battery, the initial current will be due to this and only after a second will the electric field in the wires reach the light bulb and it start conducting properly. (Assuming a perfect conductor)
Yes. That is how I understand it too. Because the wire is zero resistance (and assuming battery internal resistance is zero too) it basically acts like a transformer. Electron in the light bulb will move in the opposite direction of the electron in the battery.
So the the energy travels only 1/c but the electric field needs to travel at the very long cable first that this process can start. right?
@@louis5176 no, it travels at d/c where d is 1 meter in this setup. It's a rather important distinction because if you have two meters it's be 2m/c
@@louis5176 The electric field that travels from the battery is the main source of energy that you want to power your bulb with, the energy that travels through air at that 1*m/c is only a really small fraction of that.
If you can power your light bulb with some microwatts of power, you can light your bulb, no problem, but he fails to say anything about this in the video.
I agree. I’m not sure it would be a “voltage spike” at 1/c though. As the long wires are parallel and zero resistance.
As the voltage wave travels down the wire, it’s continually being coupled to the other wire. This would happen till the voltage wave “turns the corner” and starts it’s return back to the lightbulb.
Assuming lots of ideal components I wouldn’t be surprised if the voltage at 1/c was a constant.
Edit: that is of course till after 1 second where it won’t be constant anymore.
I suggest a follow-up which considers what happens if the wires at the far ends are disconnected. The first second after flipping the switch would be exactly unchanged! At first I thought this meant "clearly that means the bulb would be off". But the linked slides convinced me that the antenna mode is really big enough to power the lamp.
Once you start thinking about the tips-disconnected scenario, you start seeing that this looks like one big wireless charger. The antenna mode of those is big, because the distance vs wire length is comparable. That's what we have, and I found it pretty convincing for this scenario too. If powered with DC it will stop transmitting power once the ends are reached and the fields settle, but until then there's enough antenna mode transmission to power the lamp. Would be a cool follow-up.
Can you verify this with an experiment ?
I would say things got mixed up badly here. Derek is not implying any antenna-mode transmission, his thesis is that, since the Poynting analysis of a steady-state DC circuit shows energy flowing through empty space into the bulb, then it won't matter if we broaden the sides of the circuit to an egregious length. The energy will still flow the same way, straight into the bulb. This is wrong.
What you're talking about, and what was already discussed prior to the video in Derek's quiz, is the antenna-mode transmission. While it's definitely happening, the power of this mode is significantly lower. If you literally connect a 12V battery that's just about enough to light up the bulb, don't expect the same to happen wirelessly. There will be some signal there, but nowhere close to lighting up. So when Derek shows the bulb lighting up instantly, and also steadily glowing, that's not happening due to antenna transmission.
@@MarkoTopolnik I think you can also think about the super long parallel wires as capacitors, also explaining why the energy transfer starts right away, but very low, and grows over time. It's just an extreme case of every transmission line having capacitance and inductance and effects between adjacent wires.
I asked myself the same question but would like to see a more in depth analysis of what happens to the field at any point and time in the system and how the power of the bulb changes over time.
Question. If the wire is long, all the way to the Andromeda galaxy. And over there, a little green man will cut the cable and start transmitting a signal like a telegraph. After what time on earth will we notice that the light bulb starts to freeze?
a) After 600 light years due to cable length?
b) After a few nanoseconds due to the proximity of the battery and bulb?
It's disturbing that I successfully graduated high school with entirely wrong concepts. I could've died like that if possibilities didn't bring me here.
I think maybe you didn't emphasise enough an important point that might clear up some of the confusion. The motion of the electrons (current) in the wire DOES have an essential role, just not the simplistic one people usually assume. The electromagnetic field is the thing that carries the energy, but the moving electrons in the wire are a key part of creating that field. Otherwise you could get rid of the wire completely and still expect the light to switch on, which it obviously doesn't.
For example, right after you close the switch, the electric field of the battery starts pushing electrons through the wire, setting up a current. This current only exists in the wire in the immediate vicinity of the battery at first, because signals are only transmitted at finite speed. But this initial current induces a magnetic field in its vicinity, which (along with the electric field) propagates through the air to the light bulb, causing it to turn on, as you explained. Meanwhile, the electric field created by the battery continues propagating down the wire (at finite speed), causing the electrons farther and farther away to start moving, until eventually the electrons in the entire wire are moving. As each part of the wire gets a current in it, it sets up its own magnetic field, which propagates through the air to the light bulb, giving it more and more energy until the entire wire is contributing. And although the light first switches on in a very short time in your example, it does not have its full light output until the current has had time to flow through the entire circuit.
In other words, although it is indeed the field that is transferring the energy to the bulb, it is the motion of the electrons in the wire that is setting up the field that transfers the energy. This is why you can't keep the bulb on (at least past a certain time) if you remove some or all of the wire: the electrons will be pushed up to the end of the wire and stop and accumulate there, thereby repelling the electrons behind it and stopping all current flow in the circuit, which stops the magnetic field from being formed, which ultimately stops energy being transferred to the bulb. So the electron flow DOES play an essential role in the process, just not the simple mechanical role that is usually portrayed.
Right, this sounds pretty credible. So the correct answer is: yes the light turns on almost immediately, but only slightly. It then takes a second to reach full brightness.
This made a lot more sense for me than the video did
To add to this, the magnetic field strength drops off with the square of the distance, so the contribution of power from the wires near the battery terminals is negligible.
Still doesn't sit right with me though. What if the wire loops were half a light second long as before, but then had a tiny break in the end of one loop? If this is the mechanism, it seems to suggest the light would turn on without there being a complete circuit.
So when we cut the wire, electrons starts accumulating at end of wire? If so, after one year should wire get thicker at end assuming DC power supply is constantly provided to this open circuit?
I see what you're saying there about how some energy would flow through induction in 1/c time, but I feel like that's a bit of a cheat answer. I think many of us know about induction and cross-talk, but that isn't what we are generally talking about when you say "what turns the light on". That would never be enough voltage for threshold current on the most efficient LED, nor the visible emission temperature of the lowest wattage incandescent. I agree with what sandman said about how you have to consider the wire as a wave-guide for the electric field.
exactly!
Thank you! Exactly!
Exactly. The wire is a waveguide for the EM field and the Poynting vector cannot overtake the EM field. Veritasium is wrong and his fraudulent experiment here gives a false impression that he’s right. Very disappointing.
@@lradmclovin9 The crux lies in the unshielded nature of the wires and how close they are to each other. I suggest you go through the additional slides linked in the comments
High school physics teacher here. I confess to teaching the "simplified" (i.e. incorrect) model of electrons being carriers of energy in a circuit, though we do extend this to the concept of fields once the fundamentals are understood. I am generally OK with lying to my students in the sense of "start with simple models, and then add layers of complexity as needed / as available."
I literally had one of my students email me this video asking me if it is right, so I watched it. Knowing what I think I know about electricity, I agree with Green Lungo on this. I answered the question BEFORE the "assumptions" were stated. One of the assumptions is that the bulb goes "on" as soon as (any non-zero) current goes through it. If we accept this assumption then I agree with the given answer. But if you (somehow) managed to do this as described, with a real bulb (and superconducting wires etc.) then I am confident that no light would be seen coming from the bulb until the fields have propagated *through* the wires. To be a fair question with the intended answer, the assumptions should have been made very clear before providing the question (and multiple choice options).
We need at least a mini series about this.
This is so insane that i still don't understand.
Dispites the effort he did to explain the concept I still don't fully understand it yet. This is hard to grasp. Or I'm too dumb LOL
@Floppy Disk Well seems like most people are confused here so you are just in the average you aint dumb 😁
Same here, damn!
@@winter-survivor No, you're not dumb. He teaches as professors do, which is not always good. Many professors have difficulty putting themselves in students' shoes. I'm not bashing professors, just my observations from 4 years of college.
@@JohnnyAngel8 yeah they understand the concepts too obviously for them hard to explain to someone that has no idea about it