I thought this pinned comment could be a good place for people to add (respectfully) things in history and physics that you think I made mistakes on or need more clarification. Please nothing about sound quality or other superficials in this thread. Let me start: I wish I had added that when a battery is in a circuit the chemicals take a while to react, so that the electric potential difference from the charge distribution Delta V is less than the emf, or the chemical potential energy per charge. The equation becomes Delta V = emf - ir, where i is the current and "r" is the internal resistance. This is why a battery heats up when you have a lot of current flowing through it. 11
I sent you by email the PDF of a highly relevant paper on the very subject (Galilia and Goihbarg, 2005). You did not use it. Have you got it? BTW, I also think you misstated something about Feynman because you first agree with him and then seem you say that the same quote is nonsense. I've made a separate comment on that.
I'm currently working on a video debunking his video about the direct downwind faster than wind cart powered only by wind. I was going to do do a video about the DC electricity video. To me this two are very similar and both have to do with understanding what energy is and the fact that energy storage is as important as friction in physics but much less disused. My simplification of Derk's DC setup will be using a charged capacitor instead of the DC battery and a discharge capacitor instead of the light bulb. I used this analogy and people have a hard time understanding why after the switch is closed assuming the two capacitors are identical just one fully charged and one fully discharged why only half of the energy will be in the two capacitors as half was lost as heat in the wire then radiated from the wire to the outside. And yes the switch is a capacitor and you can transfer energy to the light bulb by only moving the contacts closer to each other without closing the switch so mechanical energy used to move the switch contacts will get dissipated as heat including in the bulb filament but no energy has left the battery if you return the switch contacts to the original distance.
The energy required to charge 30, 000 KMs of conductor, seems to be the limiting factor till quantified, the problem can continue being solved from there. Quantum is a synonym of the word magic, it only remains so till explained using correct nomenclature rather than ambiguous bucket-terms.
Why do you jump from one name to other, then continually admitting you did not understand, did not learn it and you disagree. Your only credentials is that you showed up in the class and looked at many science cartoons. Fineman put science on the map, what have you done?
Alpha's video proved, (in my view) that a transmission line is not the same thing as power supply. If the wires coming from the battery were perpendicular to the wires supplying the "bulb", you wouldn't even see much of a spike. And in any case you would not see continuous power.
@@zhoufang996that video of Voltage waves is totally amazing and stunning. It truly makes the behavior of Voltage look like water. I'm a student in Electrical Engineering and I can't stop thinking about that freaking video.
When I was studying Electrical Engineering in the early 1960's we first studied DC and Steady State AC circuits at lower frequencies. Then later we took a class in Transient Circuits and that introduced the concepts of electromagnetic waves and high speed transient effects of electrical conductors, spacing, conductor geometry, electric fields, magnetic fields and high frequency effects on circuits. Then we studied transmission lines, waves and antennas which then lead to Smith Charts and impedance matching and wave lengths, etc. I think what got Vertasium confused was conflating the 'transient' charge effects with the 'steady state' current/energy flow. Certainly an oscilloscope will see a 'pulse' of electric charge after the switch is closed but the light bulb required steady flow of electrons to create an (I^2 x R) energy flow to heat the filament and then create the light energy. Those two events don't happen at the same time. If all we wanted was to create an electromagnetic pulse then our house wiring could use hollow copper wires or 'wave guides' as microwave antennas us to move electromagnetic pulses around the house. However we need electrical energy to continuously flow to light bulbs and move motors, etc. so we must use 12 Gauge wire to move 20 amperes of current in a continuous manner to move energy without overheating the wire as the National Electric Code requires for all houses. The center of the wire as well as the outer part of wire all matter when you are transmitting DC or 60 Hz AC current flow to light bulbs, appliances, motors, etc. Of course if you are transmitting megahertz frequency signals to an antenna then the rules change but that is a different matter as I studied in college. Thanks Kathy for helping clear up the differences in electrical concepts of current flow.
The only difference between AC and DC is whether the current flows through the valence electrons or the conduction band. While the conduction band is closer to the heart of the molecule it is not the "center of the conductor". It is not like the "flow of water in a pipe" that's a blatantly false analogy. Electron drift is from negative to positive. The flow of current is from positive to negative. In the opposite direction. The charge is a virtual photon that pops in and out of existence as the electrons oscillate up and down their respective bands of energy. Most importantly the charge flows in the "holes" left behind the electrons. Not through or in the electrons themselves. That's why plasma physics requires ion's with electron-hole pairs.
@@calinbeale2634i think what everyone keeps getting at is "skin effect" which is frequency dependent depth of conduction. high frequency signaling results in charge density nearer the wire surface. the switch closure could be considered an impulse, which is all frequencies but the initial edge will likely be the high frequency portion exhibiting the skin effect followed by the quiescent dc state. when you look at the voltage signal on the wavefront it's a step function... high frequency initially followed by zero so the depth of interaction should be increasing with time. i would posit both components will raise the filament temperature. but the DC component will result in vastly more power dissipation, which makes the light.
I think Derek's imaginary circuit should have had two switches, one on each side of the battery terminals and closes the 2 switches simultaneously to see when the light bulb lights up? Of course, oscilloscope probes place after each switch, may be Veritasium just published the videos for the views only!
@@calinbeale2634 I was under the impression that valence electrons in a metal are already delocalized into a conduction band and that it is these delocalized electrons that are available to flow in a metal wire, either in a consistent direction under a DC electromotive force or in alternating directions under an AC electromotive force. At low frequencies, such as those used in utility grid transmission, I don't believe there is a distinction between the transport mechanisms for electrons through a metal conductor for AC relative to DC. At higher frequencies, we have to consider skin effect, but even then, I believe it is the same "sea" of delocalized electrons that makes conduction possible.
@gracenotes5379 the one thing I would add is that it is not just the conduction band. The CB is a shell for electron orbital closer in to the molecule. The valance band is a lower energy electron band where the "free" electrons float in a cloud. The electron oscillates between these two shells. When it goes up a band it's because it accepted a virtual photon and gained energy. If it goes down a band than it gives off the photon losing energy. It is the passing of virtual photons that is the electromagnetic wave.
I was one of those electrical engineers that reacted to Veritasium's video in a manner that can be best described as "wait a minute, that explains nothing". It's true that an electromagnetic wave needs no conductor, but DC current most certainly does. A lot of debunking of this has been going on since, and lots of good ones at that, so i won't go in to more detail here, but just saying that an explanation with the transmission-line model would have made perfect sense, and that the DC (battery) was a really bad example. I can see that you have been thinking both long and hard about this, and your result is excellent! What bugged me most about Veritasium's claim was the headline "electricity doesn't flow in the wire", well how else can you explain DC current? I'm really looking forward to more of your video's since i find that the historic connection is giving me a firm foothold of understanding, it makes me more grounded, so to speak. (pun intended) :-).
Another EE here. Yes I agree the transmission line model would clarify a lot, and it would explain that the light-bulb mostly likely will slowly ramp up in steps, as you see the reflected wave going back and forth between battery and light, that each have a different impedance than the characteristic impedance of the wire pair. If you look with a scope at the end of a not-terminated T-line you see exactly that. However, the pointing vector does work, even in electrostatics. I applied it myself when I wrote a field simulator (MOM based) to calculate the energy transfer. In this case you need to integrate the pointing vector over a closed surface surrounding the battery or the lightbulb. Voltage is only defined in electro-statics, and doesn’t work well if you have changing magnetic field. When we define voltage for an AC circuit, we use a quasi-static approximation.
Nobody seems to realize that these wire pairs are in fact a networks of resistors and capacitors (transmission lines). Dave and Electroboom get it. But I think this video and Derek's video don't seem to understand it.
@@kriswillems5661 I think Kathy said she had a graduate degree in electrical engineering. If so, she definitely knows what a transmission line is. BTW, you forgot inductor. 😛
@@kriswillems5661Kathy mentions dc circuits, and steady states, but in my non-qualified opinion, the fundamental thing here that closing the switch on this battery / wire / lamp situation creates, for at least an instant, a non-steady state between the two steady states of off and on, and for that intermediate instant this arrangement behaves as an AC system, which is why transmission line theory explains what is going on. Overhead HV transmission lines have a capacitance to ground of several nF/KM, this experiment doesn’t need a light-second’s length of wires to illustrate, electricity leaking away in an AC distribution line is well understood.
@@WarrenPostma so if we have perfect circle od wire (length 300 000 km, diameter 95541 km ) and we push the switch, will that signal travel just one second ?
Alpha Phoenix just posted a video where he measured voltage at multiple points along a wire. His animation of those voltages wonderfully shows the flow of electricity through a wire after a switch is closed.
Thank you, that was exactly the video I was thinking about when I posted my comment above about transmission lines. The theory is very well established.
@@laurenpinschannelsobviously the veritasium video is already out there. I think this IS an actual example of peer review, in the same way that a response paper would be a form of peer review in the general sense of the phrase.
In order for there to be peer review, the reviewer must address the subject under discuusion, in this case the Poynting vector. All Kathy does is to profess a dislike for it and for David Jackson who includes a discussion in his book. Kathy claims to be a physicist, but seems unaware of the Poynting vector until the present discussion. I was introduced in my junior E&M course and saw it again in graduate school. The Poynting theorem is simply derived by dotting the E vector into Ampere"s Law and then rearranging to form a conservation law for electric energy. The Poynting vector certainly describes the flow of EM energy through empty space. What is needed here is a discssion of the Poynting vector in dc circuits. Kathy throws up a lot of irrelevant facts but never gets around to the real issue. She does make a glaring error by saying the the electric field is the (negative) gradient of the poential, which is only true in electrostatics. In electrodynamics, one must also have a vector potential to account for the unconservative nature of the electric field due to Faraday's law.
Part II about Feynman: I believe that he was speaking to religious zealots and other crackpots who are eternal science deniers. He was NOT claiming that you can't explain things to children. I do think you have misinterpreted his words.
in fact feynman was great at breaking things down and simplifying in order to explain them. He just was opposed to saying that the simplified way is how it works. When you simplify something in order to explain it, you should say that it's simplified.
@@tommihommi1 I totally agree, that is the point of the Feynman diagrams and the "shut up and calculate" statement, he was always trying to show that the world is strange and wonderful and how things work as opposed to how we understand things work as they can often be mutually exclusive and that is what science is about teasing those two things apart to see what is real.
@Weirdly_wonderful I think I agree with the other commenters, here, about your take on Feynman's quotes which you said were about "education." I don't view the segment that you used about education or about speaking as "handed down from on high," the way you seem to be suggesting in your video. The clip you used was from the beginning of his 1979 University of Auckland lectures describing the theory of quantum electrodynamics (for which he and others shared the Nobel prize). When viewed in the rest of the context of that video (and especially that segment of his first lecture in the series), my interpretation of what Feynman was describing in that quoted section of video was "I am not going to make a fake analogy to give you some false impression about how this theory works, but because of how crazy the calculations look, or how strange the conception of the models may seem, you may not accept the conclusions we get to draw from this model and conception of how nature works. If you don't like that, you're either welcome to move to another universe where the rules are simpler, or try your hardest to come up with a different explanation and conception that fits what we've observed." In my view, this just expresses Feynman's personality and general commitment to not taking shortcuts in trying to give explanations for how things work (according to "the human beings who have struggled as hard as they can to understand it"). He says he can't make it simpler, because at that time (and as far as I know, even now) we don't have a simpler conception of how nature works, at that level (explaining quantum electrodynamics). But in my view, it is not a general remark he is making about explaining all of physics or a general remark about the nature of education. Would you agree with that?
Totally agree. Wasn't it Feynman that said "if you can't explain it to a child, then you don't understand it yourself" (or something to that effect)? So no, I don't agree with Kathy in her view on Feynman.
Love these videos!. Earlier today, AlphaPhoenix put out a video called "Watch electricity hit a fork in the road at half a billion frames per second" with some interesting observations and visualizations on DC electricity.
@@Kathy_Loves_Physics It is wonderful. I get lost in the technical explanations, so I'm not sure Alpha Phoenix's video is directly or tangentially relevant to Derrick's video or not, but it seems so.
Eric L Michelsen touched the right point. I suggest reading Oleg D. Jefimenko’s Electricity and Magnetism, topic 9-5. Displacement Field and Static Charge in Current-Carrying Conductors for clarifications about the static fields in conductors when steady current densities are present. Jackson’s 1996 paper indicates this when saying: “With the early notable exception of Jefimenko’s book, intermediate or advanced texts are no better”.
Veritasium is often off the wall and somewhere out in left field for fake shock effects. People in YT just to grab a mega audience and make money doing so. You rock, Kathy. The truth wins.
Another very good response to Veritasium's videos. One of Derek's reasons to make the original video was to spark discussion. I think you misinterpretted Richard Feyman's comment about keeping it simple. Einstein once said "God does not play dice" The response was "Eistein, you cannot tell God how to make the rules". One of Feynman's strengths was, "if at first you don't understand what you are looking at, then don't say physics doesn't make sense. Try looking at it differently till it does ".
You confused me when you first present Feynman as rejecting the Poynting vector theory, but then state that you reject Feynman's material on the Poynting vector. After checking the Feynman text in its proper context, I noticed that he gives further explanations why it "isn't so terribly puzzling" after all, with the right way of looking at it. Btw, in the "go somewhere else" video Feynman was NOT saying that some people may just be too dumb to learn physics. He is just criticizing people who have decided to reject stuff like quantum mechanics and relativity because it is "too crazy". Feynman's reply is that if you don't like this crazy stuff, go to a universe where the rules are simpler. And it mystifies me why you should even consider discounting the physics work of Feynman just because you (falsely) believe you disagree with him on a point of pedagogy. All in all, this video does not paint you in a very good light at all.
If you listen to Feynman he actually says that the theory (Poynting vector for energy flow radially into a DC carrying wire, etc.) is correct. He further says that our intuition does not match the theory but this is ok. Poynting (1884) shows that the energy (per unit time) flowing radially into the wire is actually the same as the power given by the much simpler, V*I. V*I is just much easier to calculate than the Poynting vector but it doesn't say anything about where the energy comes from (the E and B fields). All electromagnetic theory has to be expressed in terms of fields, the 'flow of electrons' is just a sideline. A full treatment would of course use Quantum Electrodynamics whuch brings us back to Feynman 😁 (Melrose's Quantum Plasmadynamics, may be a better jumping off point for someone interested enough to do the full calculation or at least draw the Feynman diagrams).
I've looked at almost all the comments. It seems Kathy doesn't want to respond to critiques that the Poynting vector is correct for DC circuits. She took Feynman out of context. Her rationales for not trusting the Poynting theorem are not strong enough and don't stand up to scrutiny.
Well, I made some work about Poynting vector especially in quasi-static cases (in the circuit frame). According to me, there is nothing wrong with the present theories, only a poor understanding of the Poynting theorem I am afraid. The Poynting theorem doesn't say anything about the actual flow of electrical energy. Worse it gives infinite possibilities to define the energy flow through a vector field, all leading to the same balance. I have shown in one of my articles (published in the AFLB journal), that you may define an energy flow in a capacitor not going outside radially but axially (parallel to the wires) as your intuition suggest, with the same overall balance. More technically, you can add any rotational field to the Poynting vector without modifying the energy balance. Discussing where the energy flows from one point to another point is pointless :-) both in Maxwell frame and in the QED frame (In the quantum frame, the trajectory of a photon is not more defined). You may consider the flow of energy in the wire, or outside it like Derek and many others, or in circles as Feynman introduced in its course to illustrate the idea of the indetermination of the energy flow (you should have followed the entire course instead of extracting only a short portion of it !). If people generally use the cross product definition it is because it is clearer to describe waves propagation in vacuum, and also because its a relativistic invariant, but this is another problem we may discuss another day. The philosophical question about the actual path of electrical energy flow remains open I am afraid !
Thanks; I was very confused by the Veritasium video which I was never able to digest. AlphaPhoenix just posted a series of videos that made much more sense in which he modeled charge as waves as it moves through wires. It struck me as logical and well presented, and so is a strong recommend.
Yeah - there is just one problem. Shinola gets 20Million views and a $100K check from youtube. Science gets 2000 views and lucky if it gets to million.
I think Feynman's quote to be one not about education but one about the scientific community. I like this take quite a lot. To me it's in the same vein as Tyson's "The universe is under no obligation to make sense to you"
Agree. Feynman was very much in favor of education and explaining and there is much evidence for that view. Here he is pointing out that he's going to be brutally honest in giving an explanation and won't oversimplify it for the listener, which would be dishonest. He says the same when explaining quantum mechanics of light. I love your history lessons Kathy !
@@fotrj No, he wanted people to accept the concepts of modern physics even if those concepts go against our intuition. If some lay person tells him "time dilation is absurd, your math must be wrong, come back with something better", then he will tell that person to go somewhere else.
I thought seriously. about creating lots of new accounts so I could like this video a bunch more times... Kathy, thank you so much, I still have tears on my face because of your kindness and humility, not to mention all of your hard work.
Have you seen AlphaPhoenix's recent video? Especially his second channel further explanations about impedence matching? I find it a great explanation as well.
I'm Eric L Michelsen, but Google is scrambling my name. To clarify, I'm affiliated with the University of California, San Diego (and my last name is spelled "...sen"). There is much interesting and useful material in this video. For example, I have given a talk describing simple experiments which show that power does NOT flow along the Poynting vector, and that is fully compatible with electromagnetic theory. For reference (but not claiming infallibility), I have a BSEE, and a PhD in physics, and decades of experience in laboratories and measurements; I teach this material at the upper-division college level. However, I think it is well established that the electric field inside a current carrying wire does, indeed, drive the current, and that this field is created by surface charges. Conductors can expel E-fields only in a static (or quasi-static) system. In contrast, a DC circuit is a steady-state dynamic equilibrium, and though the charges in the conductor move to reduce the E-field, the battery is constantly "pulling" them out of (and "pushing" them in) the wire, so they can never cancel the E-field completely. It takes only a tiny E-field in a good conductor to drive a significant current. This is established by extensive experiment, and organized into the detailed theory of electromagnetism (with no deference to anyone's authority). I have a detailed discussion of the speed of electricity and the Poynting vector in my "Funky Electromagnetic Concepts" (at the bottom of my web page), starting around page 69 (as of this writing). I performed (the moral equivalent of) Derek's experiment, and confirmed that in some very realistic situations (but not all situations), the bulb turns on nearly full brightness, nearly instantly (as expected from theory). My document includes photographs of my setup and results, and a discussion of the theory, but is written at the upper-division college-physics level. This is all well-established science, and fully consistent with relativity. (In Dr. Muller's follow-up video, I think he actually didn't give himself enough credit for his prediction.)
When you close the switch, positive charges start to spread on the plus pole, and negative charges start to spread on the negative pole. These charges cause on electric field. On the positive side, with the positive charges, the field pushes away positive charges in the parallel wire, on the negative side the field pushes negative charges away in the parallel wire. So an unbalance is created in the parallel wire and a current flows and the light goes on. This happens after 1/c seconds, because the field only need to travel 1 meter. It's pretty simple, both wire pairs act as capacitors. And DC pulse passes the capacitors (but a continuous DC voltage does not). The continuous flow of current happens only later when the electron flow in the wire starts. This happens much later. So, the bulb flashes after 1/c seconds, but it is only stable much later on.
Love the actual experiments you’ve done! Great channel that I have frequently used before giving lectures to give some human interest to where these equations come from in the first place. Great book too!
...and I think I can reconcile two of my favorite science educators in my mind. Feynman frequently tried to be dramatic in order to engage his listeners and at heart is a theoretical physicist. Kathy is, at heart, a teacher, and to you, it is the teaching and communicating. Feynman wants the student to already have a complete grasp deep within maths. Kathy, is happy to explain in simpler terms. I like Feynman. I love Kathy. I have Feynman's lectures. I watch and re-watch Kathy's TH-cam stuff to refresh my mind and reeducate myself for all the stuff I forget or forgot. Thank you, Kathy, for making me very happy. Thank you, Richard, for your contributions to science, too.
Feynman is happy to explain physics. He does that in his lectures. But he will (very obviously) refuse to bend physics just for the sake of people who reject concepts that contradict their intuition. That was his whole point. It had nothing to do with how to teach physics. Kathy misunderstands Feynman completely on this point.
What Feynman was saying is that the universe has no need to be simple ---in terms of linear, intuitive to human understanding etc---and that one must accept experimental evidence over a neat simple concise but wrong theory. In terms of his views on education, there were two main sentiments expressed: 1) If you can express something in a way that ordinary people can understand,,then the likelihood is that you don't understand it as well as you think (that's his famous meme on learning) 2) Somethings in nature cannot be explained without first explaining a whole gamut of mathematics except by analogy. The second sentiment was expressed in an interview where the interviewer had asked him to explain how magnets work and why. Feynman could go only so far before he needed to upgrade the individuals maths skills. I think that your notion is entirely true in that: anyone should in theory be able to understand anything scientific; however, the depth of understanding does depend upon having or possessing mathematical ideas once you go beyond certain levels of knowledge.
I'm sorry but that's really not how batteries work. All chemical cells are based on specific redox reactions occurring within them. Some of these do use acids or bases and metal electrodes as their reagents but others do not. Their common element is that half of the reaction (reduction, which consumes electrons) occurs on one electrode and the other half (oxidation, which generates electrons) occurs on the other electrode. The simplest cells will achieve this by making the electrodes from the reagents, but _there are_ plenty of cases where one, or both electrodes take no part in the reaction. You can keep the electrodes in two different solutions connected via some sort of an ion exchanger. You can cover the electrodes with a catalyst. There are plenty of options. And second of all, when the battery is not yet part of the circuit, the reaction indeed isn't occurring. But that doesn't mean it can't give you current right away - as soon as you complete the circuit. The reaction isn't progressing precisely because it has progressed the furthest it could get, building up charge on the electrodes, internal wires and the terminals. And finally, the heat generated from resistance is frankly negligible. The vast majority of heat will be produced in the chemical reaction itself.
The electric field inside a wire is only zero when there is no current in it. If it's carrying a current and it has resistance, there will be a charge gradient along it and therefore an electric field.
The fact that people are STILL posting responses to that video gives me faith in humanity. I watch them all and every one teaches me something new, a slightly different perspective for thinking of how electricity works. Great one from Kathy here, with an illuminating historical perspective. For all the problems of that original video, hats off to Derek for pushing many of us to look beyond the elementary school depictions of electricity.
I am a BSChE about ready to retire in 15 mos. Going back to my alma mater to get a degree in physics. Been watching MIT OCW (diff eq to refresh after 40 years) and Elliot and ViaScience... and you... and some others but your videos are fantastic. Thanks Kathy!!!
I admire your videos. But now, i'm in love into them. You're great communicator and reinventor of old wonders and stories. Thank you for the great work. Looking forward to more videos
I think energy is just an accounting thing in physics. Energy is defined as the ability of a system to do work. If a system do work then its energy is decreasing, and the energy increases on the other system that the work is done on. This continues until both systems are in equilibrium and neither system can do any work on the other. The physical thing here is work and not energy. Like in accounting, my work is the physical thing and the money I get for it is just an abstract accounting number. So energy doesn't really "flow" as in something physical like water flowing in a river. Something physical must do work. "Energy doesn't flow in wires" is really nonsense, energy doesn't flow. What happens is that a field is created, that field is doing work, pushing the charges, those charges collide with other charges, change the orbitals in the bulb, those orbitals decay releasing a photon (which is also work) and the light bulb lights up. Mass as a form energy comes also from work done. About 99% of mass comes from the complex interactions of quarks and gluons in the proton, which is work. 1% of mass comes from the interaction with the Higgs field, which is also work.
It feels like you are taking Feynman’s comments on the Poynting vector out of context. The Poynting vector is a measure of energy flux, and that’s by definition, there isn’t anything to argue about there. What he was talking about is a bar magnet next to a battery, where no power is either provided or dissipated, but the Poynting vector is non zero, seemingly indicating that energy is flowing in circles, which is not intuitive, but is still true. To say that the Poynting vector doesn’t work at DC, or that it isn’t accurate is wrong, it works because it is defined to work, it is an extension of Maxwell’s equations.
I think this wholly comes down to semantics and what it means to "light up" the bulb. It also seems to have some relationship with the difference between the maximum speed of causality and the propagation speed of "meaningful" events in the physical world.
Actually, as you well know, Feynman did a a great deal to make physics understandable to people. Who is perfect across all areas at all times in their life.
Honestly, I don’t understand your confusion. I don’t think it’s good for someone to put something that they think is obviously nuts and crazy in a textbook. Also, I do not know that he did “a great deal to make physics understandable to people”, as I’ve never seen a single example of that. I’m not asking for perfection, I’m asking for kindness. But I have not watched/ read everything that he did. Maybe he was kind and relatable in other areas. I just haven’t seen them. Also, we are allowed to have different opinions. I’m allowed to think negative thoughts about Feynman and still be a physicist right?
@@Kathy_Loves_Physics absence of evidence is not evidence of absence. Seeing involves looking. Maybe you have a responsibility to investigate properly, as you do for the characters you write about, before making such a public statement. Feynman did not have the attitude you claim, quite the reverse. Disappointed.
Warren, I am particularly interested in your use of the word quixotic. Quixotic is a reference to one of my favorite novels Don Quixote where a poor farmer decides that he is a knight, and a windmill is a dragon that he cannot defeat. But I don’t get what that means in reference to my video. I mean, you could be saying that I am not really a physicist, just as Don Quiote was not really a knight. But if that’s the case, then my complaints about Richard Feman are quixotic means that Richard Feinman wasn’t a physicist either, he’s just a windmill. Care to clarify?
It is hard to separate what Feynman did and what he claimed he did. The guy was an extremely good story teller and had a sizeable ego. That and he had a very poor attitude towards women. Kathy has every right to be suspicious of him, I can only imagine the amount of sexism she has put up with in this field.
I agree fully with Feynman's statement. My interpretation of it, based on some wider context, is that he saw simplification as inherently untruthful. He was well documented happily spoon-feeding complex topics to any level of audience. The important semantic detail is that simplification of a complex thing is an arbitrary modification of the thing, and not equal to dividing the thing into manageable components for learning. Simplifications taught to children are very often a major source of trouble later in their education, and even in general life, because you have constructed a faulty foundation and now the entre first floor needs a complete tear down and rebuild before the second floor can be added. (This applies to any introduction level education, not limited to children.) In short incomplete (building blocks) and incorrect (simplified) are different things.
You said, "It was because of Feynmann's comments on education that I started discounting all of Feynmann work." This betrays a fundamental principle of science that we look at the science, not the source. Anti-scientists use this technique. "Oh, he believes in climate change, so I won't take his studies in geology seriously." Feynmann's improtant physics work was peer reviewed. So, you are also discounting peer reviewed science, including I suppose quantum electrodynamics. I also have to point out that the lecture you showed a clip of was Feynmann at a QED lecture. The audience would be expected to understand his point. Facts (and observations) are the proper test of theory. It was completely irrelevant as to education of children. So, clearly taken out of context. Real context: In April 1966, Feynman delivered an address to the National Science Teachers Association, in which he suggested how students could be made to think like scientists, be open-minded, curious, and especially, to doubt. (From Wikipedia)
Well, people often make the mistake of confusing the message with the messenger. It's actually a logical fallacy. If you want to attack an argument, attack the argument - not the one who is putting it forward. However, confusing ideology with how the world actually works is often producing this result. Which is a pity, because by very nature any ideology is internally inconsistent.
I love these historical perspectives! Much of modern science communication is so difficult exactly because it is unaware of the original progression of discoveries that made us understand these processes in the first place. I think we should teach most topics by repeating the original discovery, with newer information only added in where they really make it easier to understand.
5:59 Wait: "static charges don't affect field in the conductor" is only true if there is no electric flow. Imagine a battery short-circuited with a wire from + to -. Now draw a closed loop through the battery and the wire. Along the wire, inside the wire, voltage goes from +1.5 V to zero, therefore there *must* be a field inside the wire too. Charges are constantly moving in an effort to balance out this field, but can't because of the external (chemical) energy source.
@@supermikeb yes exactly. Kathy is citing the rule that applies when there is no flow, while Electroboom is talking about a situation where there is a flow, balanced by a resistivity.
With dc it's the electric field IN the wire that drive current and power IN wire and ac will be totally different. Sounds like you are correct. Great video. Thank you
5:57 "Static charges do not affect the electric field in a conductor" That is *remarkably* false. What Michael faraday discovered and whats actually true is that the electric field inside a conductor in electrostatic equilibrium is Zero. The simple reason is that a conductor can be seen to a fair degree of accuracy as a material with free electrons in it, this means that if there was an electric field inside these would feel a force and therefore they would move and that wouldn't be electrostatic equilibrium. For a conductor that's not in equilibrium this statement is completely false, in fact, for a conductor to not be at equilibrium there MUST be a force moving the electrons inside it. This is such a major mistake it undermines the credibility of the whole video, and not the only such mistake btw.
Very interesting video. I'm curious if you have seen Nick Lucid's "Science Asylum" video from about 4 years ago titled "Circuit Energy Doesn't Flow the Way You Think" and what your thoughts might be about it.
I'm only 1:15 in, but I love you already Kathy. I am not a scientist, but when I first watched the video at Veritasium, I was deeply disappointed by his simplistic approach. I am reminded of the fact that science progresses because good theories get replaced by better theories. NOT because of bad theories being replaced by good ones. It is a process I refer to as "Continual Refinement" and I try to apply that process to myself. And of course we must understand that Kuhnian paradigm shifts take place in science, and how messy they can be, because science is performed by humans with big egos.
I think I miss something. You seem to agree with Feynman around 7:20 and 8:00 but then disagree with the same quotation around 10:15. What did I miss? PS. The third instance of the Feynman quote (20:45) makes it even more obscure to me. What is pseudo-science here? Feynman's lecture or treating the Poynting vector as an energy flow for the case of DC currents?
Kathy is delusional here. What Poynting says is no word salad. Its 19th century physics terminology but perfectly correct. And Feynman was wrong if he meant that "absurdity" literally. The "absurd circulating energy" form static electric fields and static magnetic fields has been measured. More specifically it predicts that there is momentum from this circulation and that momentum can be measured. This is all far less "absurd" once you realize that a magnetic field in the classical picture requires charges to move. There is nothing "at rest" once you include magnetism.
@@michaelrenper796 I think Feynman means that this may be mathematically correct but is physically meaningless. If this is measurable, as you claim, he is wrong. Can you give me some quotes to this effect? Preferably to original scientific papers.
@@michaelrenper796 OK, so I can forget all you said and stick to what Feynman taught (usually not a wrong choice) as you seem to have nothing to support this claim. And I almost believed you for a few minutes. PS. I looked into the literature and although some papers claim that this Poynting vector interpretation is necessary to provide conservation of energy and momentum (not a big surprise), I could not find one claiming that this is actually measurable. Some even postulate using a "hidden momentum" to cancel out the Poynting one. As I said, total confusion.
The Poynting vector itself does not represent energy flow. If you integrate the P. v. around a closed surface, the result is the net energy entering or leaving (depending on sign) the enclosed volume. Alternatively, the divergence of the Poynting vector indicates if a locality is sourcing or sinking electromagnetic energy. Feynman was addressing the view that the vector itself represents energy flow.
But note that Feynman does agree with the theory which is "obviously nuts". His point is that the theory goes against our intution, but that does not make it wrong (and if you don't like it, then I guess he'd say you can go somewhere else). Feynman also points out that the practical consequences are near zero, and I very much doubt that it has any real relevance to Derek's question. "Energy" is anyway mostly a bookkeeping device.
@@ronald3836There is this one experiment that you could theoretically do where you measure the gravitational field generated by the energy and energy flux distribution. However carrying such experiment in a lab is beyond current technological capabilities and as far as I know no one has postulated a way to do it with astronomical observations. This video was clearly convinced out of ignorance tho, she only ever appeals to intuition and doesn't provide any real argument against poyntings theorem being applicable in a physically meaningful way to DC circuits.
@@marcossidoruk8033 That would be a very interesting experiment indeed. I guess "energy is just a bookkeeping device" might not sit so well with general relativity. But I do think it is correct to say that we can't help to think about physics in terms of abstractions which the universe itself does not necessarily care about. And of course that is why we do experiments to find out how far our abstractions can take us. There are these videos about "gravity is not a force", but that presumes that the Newtonian notion of "force" is more than a very helpful abstraction.
Derek could've saved himself a lot of grief if he'd just used correct units. 1/c seconds doesn't make sense, it doesn't solve for time. Without showing where the "1" comes from, the answer appears to be the inverse of c, regardless of the wires proximity. In units, his answer is 1/(m/s)=m/s, a measure of speed. If 1meter is used then m/(m/s)=s, a measure of time.
Great video!! Im interested if the cucit, but instead treated like a large circle and not two paralell conductors (EMP travel at light speed.) will this relate back to Cosinus to f ,and electrical motors?
"EMF pulse" makes the initial energy sound "fleeting" like a pulse is. It is not. This is the misconception. When that switch flips, the electricity - the voltage and current from the battery - turns on and stays on until the main electric current from the loop catches up with it and increases it further. I think this is the common issue that engineers & physicists have, because they think sure, there's an initial minuscule blip from the switch but it's inconsequential. They are wrong: it is consequential, and it's because our intuition of electricity flowing in wires is incorrect. Maybe a helpful abstraction most of the time, maybe, but incomplete and wrong even when talking about transmission. I was confused for a minute by the initial Feynman quote about the Poynting vector being "obviously nuts" until later in the video when I realized that it was just a comment on how non-intuitive he thought it was, not that it was false or wrong. I think I understand the sentiment but still appreciate the Poynting vector myself since it is just combining the force vectors of the electric field & magnetic field.
As a lay person I've noticed that no matter the subject, a lack of historical perspective can be fatal to clear thinking. I think anyone who wants to study a science needs to retrace the path of those that went before us. Thanks for applying that principle to physics.
I remember when his first video on this came out and there was a big reaction and discussion to it. I feel it was the perfect educator situation, since it forces someone to really start pondering how all of it works before they can even start to come to some conclusion of their own. In the end, the places where he was wrong seem mainly to be from oversimplifying for pedagogical reasons, and slips of wording that were wrong or make it debatable what was meant, all of which allow for misunderstanding (since I am sure Derek himself understands this, it is more a matter of presentation). It is great that even after all this time, people are still making responses to it, and getting people engaged with the details of how it all works.
I have several comments about this video: 1) Your excerpt from the Feynman lecture is taken out of context and misleading. Taken in context, it is clear that Feynman is saying that even though it is counter intuitive and seems crazy, the standard interpretation of the Poynting vector as the energy flux is correct: the energy flows through the fields in the space surrounding the wires. 2) Your use of the expression "direct current" confuses the concept of "direct current" with the concept of an electro-static (or electro quasi-static) system. "Direct current" means simply "current that flows in one direction" and colloquially does includes what happens when a switch is closed in a circuit consisting of a battery, wires, a light bulb, and switch connected in series. The two different "steady state" conditions of "switch open" and "Switch closed" are well described by setting all time derivatives in Maxwell's equations to 0 which is called the quasi-static approximation. For a system that changes in time, such as when a switch is closed, this is approximation is only valid if you are only interested in time scales much greater than l/c, where l is the physical size of the system and c is the speed of light. This requirement is not satisfied in the described problem. 3) Your a) dismissal of the "Poynting vector" for describing energy flow in DC circuits, b) your characterization of the physics of closing a switch in the described circuit as "DC" and implying that the physics of the transient is no different from the physics of the steady state, c) your misleading quotation of the excerpt from the Feynman lectures, d) your discussion of the Maxwell equations, and e) much of your discussion of the difference between science and pseudoscience taken together indicate a lack of understanding of the meaning of the Maxwell equations. The Maxwell equations are set of 4 coupled partial differential equations which, when supplemented by the Lorenz force law, Newton's laws of motion, and appropriate description of the system understudy, including initial conditions, describes the time evolution of any electrical or electro-mechanical system for which effects due to quantum mechanics are not important. This is not controversial; the successful operation of all the electrical and electro-mechanical devises in our modern world attest to their correctness. Poynting's theorem, which is also a partial differential equation, can be derived from the Maxwell equations; so if the Maxwell equations are correct (they are) and the manipulations used in the derivation are valid (they are) then Poynting's theorem is true. Poynting's theorem is derived and discussed in all sufficiently advanced textbooks on electro-magnetism. In my library, the derivation is presented not only the Feynman lectures, but also in "Classical Electrodynamics" JD Jackson, "Static and Dynamic Electricity" by Smythe, and two volumes ("The Classical Theory of Fields" and "Electrodynamics of Continuous Media") of the Course in theoretical Physics by Landau and Lifschitz. It is even derived two books that are not strictly speaking electrodynamics textbooks: the mathematics textbook "Methods of Theoretical Physics" by Morse and Feshbach and the engineering textbook "Electromechanical Dynamcs" by Woodson and Melcher. There is no doubt that Poynting's theorem is true. The only possible controversy involves the interpretation of the terms its terms. The question of energy conservation in classical electro-magetism is discussed at length in Sections 27-1 through 27-5 of the Commemorative Edition of the Feynman lectures on physics; Poynting's theorem (although not referred to as such) is Eq 27.13, and it is derived in Section 27-3, and the quote taken out of context in the video appears in section 27-5. Contrary what is implied in the video, neither this discussion nor the derivations and discussions in the other textbooks appeal to authority for their justification; they all present mathematically rigorous derivations of Poynting's theorem from the Maxwell equations, supplemented by discussions of the interpretation of the quadratic terms in the theorem as the energy density of the electric field, the energy density of magnetic field, the rate of mechanical work performed, and the energy flux in the electromagnetic field. Poynting's theorem is definitely correct, and its interpretation as implying that the energy density and energy flux in a electro-magnetic system are both distributed in the fields is a mathematcially consistent and correct description of electro-mechanical systems. In the video you refer to the product of the charge and the electrical potential as the electrical energy. This equation is only true for static systems, and cannot in general be used to analyze a dynamic system such as closing a switch in an electrical circuit. Feynman shows that for electro-static systems the expression in terms of fields, when integrated over the entire system, gives the same numerical result as the volume integral of the product of the electric potential and the charge density, while also consistently describing the full dynamic (time varying) case. For the present case, there is no mechanical motion (the wires are assumed to be stationary), so only electrical properties are important. Furthermore, the conductors are assumed to obey Ohm's law. In this case, if the geometry of the wires is specified, including the geometry of the switch, the Maxwell equations can be solved to determine the time delay between closing the switch and the light illuminating. Except in special cases, the equations cannot be solved analytically, but have to be solved numerically on a computer. This is well understood physics, and I assert that the chance of a disagreement between the results of the calculation and an experiment. For the present case, the Maxwell Equations can be solved numerically to calculate the brightness of the bulb as function of time. This time dependence depends on the exact location of the wires, so your statement that the correct answer (if the question is interpreted as asking for the time it takes the brightness to settle down to the steady state value) cannot be determined from the statement of the problem is correct, but the strong implications that the validity of Poynting's theorem is controversial and that time dependence cannot be accurately computed using the Maxwell Equations is false. In many cases intuitive understanding can lead to accurate and useful insight, although intuition is no substitute for detailed calculations. In the present case, my intuition says that a) electric current cannot start flowing in the bulb until enough time has elapsed for an electromagentic wave to propagate between the switch and the bulb, b) the steady state will not be established until a time somewhat longer than the time required for an electromagentic wave to propagate all the way around the wire, and c) the details depend on the exact geometry of the circuit.
Re Feynman, as a fellow New Yorker (but uh, not a fellow genius) I think he was just getting at there being a level of irreducible complexity where intuition cannot take you and you have to rely on the math, stated in kind of a sarcastic way. Its ok if you take issue with that, but I don’t think he was insulting children there, just that… like, if you want a 5 year old to understand the path integral formulation of quantum mechanics, the 5 year old will need to be a 6, 7, 8 , 10, 15, 20 year old that learns all the intervening math, and classical physics. Feynman is just saying he can’t do that work for you - thats my interpretation.
Has no one ever used an oscilloscope? A scope especially with storage will show the transients and provide an way to measure them. Modern scopes can go well over100MHz and can easily capture nanosecond events. It might also be interesting to use coax instead of bare wire.
When I was in college, the professors acknowledged that the electrons flow from - to +, but to keep the math easier, we engineers cleverly came up with hole-flow theory... as an electron moves, it leave a gap, so the one behind that comes in to fill that spot, but it left a hole and the next one behind that moved to fill that gap, and so on. If you look at this gap, or "hole", it is moving from + to -, hence hole-flow theory.
As a Master Electrician and keen viewer of your videos, can you please tell me if you think electrons go forward and backwards in an ac circuit. If so, how far backwards and forward do they travel. I've looked in my text books and spoken to my associates, but no one has a definite proof. Please help , thank you . John M French.
I think veritasium video mixes two topics, the steady state and the EM pulse. EM pulse: you have to treat it like a transmission line. It will move some electrons in the light bulb about 1/c seconds later, but not enough to light it up. Bulb will light up only after the signal will be able to "check" the continuity of the whole circuit (otherwise superluminal messaging would be possible). Regarding the steady state, once all the oscillations of the initial EM pulse have been dampened out: to me it seems only a matter of modeling. The most common model is that of electrons pushed through wires. The moving charges then cause EM (static) fields as a consequence, and, curious coincidence, a Poynting vector appears. But, you could easily say that, lying the conductor in a certain way, you put some constraint on the shape of EM fields, which carry the energy and, as a curious coincidence, electrons in the conductor start to move. Either way, you can't have moving charges without fields and viceversa. Choose the model that fits best, especially, the one that is easier to apply.
Part 2. Feynman talking about CRAZY Poynting theory was not implying it was wrong but that it's crazy. He believes it correct and explains the unusual aspect of the theory in his lectures. He shows how Poynting Vector describes energy and field momentum. It's always true in EM theory that energy is conserved LOCALLY. There is a partial differental equation that applies to any POINT in any EM situation, in or out side wire. It relates energy density, work done on charges by fields or work done by fields on charges and the Poynting Vector energy flux through surface boundary of tiny infinitesimal volume. Very tiny volume because it's a differential equation and so a statement about what's happening at a point. This LOCAL energy conservation law is fundamental and this is the reason you need Poynting theory. In the infinitesimal volume when work is being done and change in energy density, you will have an flow FLUX of energy across the boundary surface which is described by the Poynting Vector. So that's why you need Poynting. It's so you can explain what you mean by local energy conservation - the relationship between energy density, work and energy flux.
Me again. So by integrating the Poynting Vector over the boundary surface you compute the flux of energy across the surface. The usual expression for the time averaged energy of a plane EM wave, that IS the magnitude of the Poynting Vector. The unit's of magnitude of the Poynting Vector is power over area, usually watts per square meter. Those hand held devices that measure radiation in an area are measuring the magnitude of the Poynting Vector (usually units of mW/m^2) Also what is called the Solar Constant, well that again is the magnitude of the Poynting Vector (unit's of kW/m^2)
Me again. Local energy conservation an objective fact of EM theory, Poynting vector is just consequence. What about the solar wind DC current, where is the energy - in the fields. It doesn't matter what type of bulb he had his point was the energy is in the fields and field nipped straight across to the bulb with a little bit of energy to set up a tiny current as well as traveling round the wire. Those surface charges and shielding, that's Gauss Law, electric statics. Shielding result of Laplace equation having unique and constant solution for constant boundary conditions. Where is the energy in capacitor, charges on plates energy in fields between plates. Energy is ALWAYS in the FIELDS. ALL your videos are brilliant and thank you very much.
Yes I understand what you mean but you are confusing electric statics and E dynamics. As l say Laplace is statics. You will still be able to receive a phone call on your mobile even in a faraday cage no problem, that's E dynamics. The Skin Effect that's electric dynamics and is how you would shield from EM waves, it also like a limiting affect for heigher frequencies becoming like a faraday cage shielding. Physics totally different tho, for statics solution of Laplace equation and for dynamics the differential is like the diffusion equation with time derivatives and solution similar, exponential factor, providing attenuation.
Yes I think you are correct tho. The point is this Poynting vector is mathematically correct but doesn't distinguish between kinetic and potential energy. For DC there will be current in the wire and energy flow inside the wire. The Poynting Theory HAS to be correct but it doesn't distinguish between kinetic & potential energy. I think that is the cause of confusion.
I thought that in the condition where the bulb is very close to the switch that the bulb would light immediately, similar to the time it would take if the circuit were of small size rather than half way to the moon (or whatever the distance was). I assumed this based on the circuit would be in a steady state prior to closing the switch and there would be a difference of charge potential across the switch, and the charge in the wire on the long end would be constant along it's length. When the switch closes, current begins to flow immediately because of this difference in potential and as the current moves along the wire it continues to provide difference of potential as the charge from the far end of the long wire eventially catches up. OK maybe I did a poor job of explaining that. It's late and I'm tired. It was fun to think about though. And no, I don't recall any mention of Poynting Vectors during my education either.
I appreciate the time and effort you put into your videos, but my utmost appreciation is towards your tone. I love how measured and thoughtful your videos are. You make the topic very approachable for the newcomer, but also have enough detail and complexity for a well-rounded presentation. Your respectful response to his video is how such videos should be handled.
Albert Einstein is said to have stated “If you cannot explain your theory to a seven year old, you do not understand it yourself”. I agree that anyone can understand any of the concepts in science if they are properly and concisely presented. I enjoy the presentations on this channel because they are presented so.
Maybe Einstein wasn't right about that. But your later statement is patently false - there are scientific concepts that are outside the reach of some humans. This is true also for me, there are things in science I know I csnnot fully grasp.
Closing a switch to power a transmission line is sending a very frequency signal on a transmission line. The line will absorb the current matching its impedance until it reaches the end, where the power will be absorbed or reflected when the load resistance doesn't match line impedance, it will take a few iteration to stabilize and then the circuit can be called a DC circuit. The all argument is a misunderstanding about AC and DC.
Kathy, I bought your book and wow, so much good dope, kudos! I love history, and electronics has been a hobby of mine since 5th grade! I am self-taught in engineering, as I have no aptitude for a school environment, exams and drinking lectures as if from a fire hose.
05:56 "static charges do not affect the electric field in the conductor" You are so wrong that it hurts 😢. Please do not mistake the electrostatic case with the quasistatic case of stationary and slowly varying currents. The surface charge (and in nonhomogeneous materials, the interface charge) does determine the electric field inside the conductor and that field is not zero. In fact, it has the value specified by Ohm's law in its local form. Go read Sommerfeld, or solve the system of Maxwell's equations along with the costitutive equation and the equation of continuity to see it.
I love your videos, I used to have electronics as a teenage hobby and one of my uncles was working as a microwave electronics consultant in the 1970s here in Australia. I identify with all that you say. Lots of love from David Newton x
The timing on this video is perfect as Alpha Phoenix just released a video about a similar thing, but his explanation of what’s happening felt a bit lacking to me.
Thank you very much for doing these well researched video topics with a lot of thought experiments that have been invested in them. Keep this going and take care of yourself. Cheers.
I had the great misfortune of having to useJackson's Classical Electrodynamics book in my graduate classes in the 1970s. It was impenetrable then, and it''s impenetrable now. Like gravity, I think we still don't really understand EM.
19:39 yes, I think that should be the goal, but sometimes it's impossible with modern physic, especially quantum mechanics. In this casecyou have to simplify and/or interpret things if you just use words. However you shouldn't go further with tjis then necessary.
I give you 2 thumbs up! I don't really understand all things electric but I do have a great fascination with them. When I watched Derick's video on how long it would take to light a bulb I felt uneasy with his explanation although I wouldn't have been able to verbalize it. Your video helped my understanding of my original unease. I also greatly appreciate your definition and comparison of true science vs psudeo-science. Thanks for posting.
It was like engineers arguing with physicists. In Electronics, we have a number of models and tools to design our gear including conventional current which is opposite to conventional flow. As a tech, I was first taught electron flow and regret it to this day. It’s like learning imperial system instead of metric. I learned about skin effect in AC but I see there’s a lot more to this than I realize even though I really don’t need to know it for my daily tasks. Socratic method of asking and answering questions to arrive at a truth…like the Paper Chase. I enjoy the deep dive down the rabbit hole to Wonderland by all the creators on this subject.👍
I started as an electronics tech in the Marine Corps, and they taught electron flow. It seemed odd that current would flow against the arrow of a diode symbol. However, that was still the era when vacuum tubes were in use, so there is some sense to talking about electron flow. That school was pretty basic, and raised enough questions in my mind to motivate me to become an electronics engineer.
@@SkyhawkSteve There was... at least some... American profs writing textbooks using electron flow (versus conventional current flow)... but, AFAIK... and apparently... it never caught on. Eventually, I think, everybody promoting electron flow gave up trying to change it.
Electricity, Magnetism, Heat, light / Color, Mass / Weight are different manifestations of Gravity and Continually convert to each other. Gravitational Particles (GPs) move by means of CONDUCTIVITY towards the CENTER of the GRAVITY. Turbines convert the Gravity Force to Magnetic > Electrical > Heat > Light and everything in between. When GP moves in the Air (4N1O) Atoms are manifested as Magnetism, therefore Magnetism exists only in the Atmosphere and is absorbed by Compass measured in Air Gap and Magnetic Flux context. When GP moves in Solid it is observed as Electricity and measured by its Power/Force/Voltage and its Current/Amps and their combination total Quantity of GPs in a unit of time as Wattage. GPs move at a 90 Degrees Angle relative to their path in [side] Steps, therefore the GPs manifested as Electricity, Magnetism, Heat and Light transit to the Outer Edges of the Medium/Matter.
I disproved Veritasium with a very simple experiment: I put a _second_ light bulb right on top of the first bulb, but without connecting it to the battery. If the electrical energy flows through the air directly from the battery towards the bulbs, both should've lit up. But only the connected one did. Derek did not respond or explain why the unconnected bulb did _not_ light up. To be fair, his video had already received tens of thousands of responses by then, and it was physically impossible for him to respond to every one of them. I also pointed out that in computer networking, the network latency-the time it takes for electrical signals to travel from one computer to another-depends on the _length of the connecting wire,_ and not on the as-the-crow-flies distance between the computers. This fact is not in dispute. This is why the stock exchanges, for example, make sure that the networking cables connecting the exchange servers with the traders' servers are all of the same _length,_ so that all traders receive trade messages at exactly the same time-to the nanosecond.
AlphaPhoenix showed it also works with disconnected lines. How did you do the experiment? Because you need very sensitive equipment to actually measure this and a normal light bulp won't actually light up visualy.
@@drfisheye Oh, I'm not disputing that an electromagnetic pulse (EMP) spreads out from the switch-not the battery, BTW-when it is closed. No doubt, the EMP can be measured with sufficiently sensitive instruments. This EMP travels at the speed of light (in air) and jiggles the electrons and protons in all the objects it passes through, including the bulb, its filament, and its glass shell. In fact, as you pointed out, it's not even necessary for that bulb to be connected to the switch and battery for it to feel the EMP. The length of the wire is irrelevant-it's just a misdirection. BTW, I'm an engineer and a licensed HAM, so I know my way around Maxwell's equations, electromagnetic waves, wireless transmitters and receivers, oscilloscopes etc. Of course, I'm not saying I understand everything-far from it. And while I use the Poynting Vector to calculate the power transmitted by an EM wave, I don't ever recall using it to calculate power transfer in an electrical circuit. In a circuit, it's always P=v(t)i(t) (or some variant). It's not that the Veritasium video is wrong. It's the fact that Derek deliberately misleads you-without being technically wrong-that bugs me. I know he has to do click-baity stuff like that to grab eyeballs. Still, I find his _"everything you know is wrong"_ attitude quite irritating. Particularly because I coach high school students for competitive college entrance exams. I don't know what kind of schools Derek went to. But here in India, high school students do learn about transformers, electromagnetic waves etc. With equations (though not vector calculus just yet). We do tell them upfront that we're teaching them a simplified version of reality, and that they are free to study more complex models later on if they wish. We teach them stuff that they can build upon later, not stuff they have to forget and start over from scratch. You teach them that the flow of charged particles is electricity, I = Q/t, P=VI etc., and they will reach the logical conclusion that in solid conductors, it's the electrons that carry the electrical energy. That mental model is sufficient for working with electrical circuits, so we don't correct it until a better model is required. Some of my students watched the video in question, and sadly, got confused about the role of wires in an electrical circuit. They argued that since energy flows directly from the battery into the bulb through space, and not via electrons in the wire, all bulbs in the vicinity should light up, connected or not. At least, that's what the Poynting Vector diagram in the video implies. No doubt, all the bulbs felt the EMP. (Though you can argue whether it caused any of the bulbs to "glow" in any meaningful sense.) However, any transient currents due to the EMP are very weak, and die down very quickly. After a short delay, the bulb that's connected to the battery starts glowing steadily-when electricity actually starts flowing through it. The length of the wire determines the delay. (There are transient currents through the wire as well, for that matter, but after a while, those too die down.) And the unconnected bulbs don't glow. This isn't obvious from the video. The Poynting Vector diagram seems to imply that if you keep an unconnected bulb close to the connected one, both should glow steadily. Easy to disprove. Harder to explain Derek's motive.
Yes I think you are correct Kathy. Poynting Theory does not distinguish between potential and kinetic energy so flow that seems unphysical will probably be potential energy. With dc there will be energy flow inside the wire.
On his original video I asked what would happen if the wire had been in a circle of the same length instead of parallel lines connected at the far ends. No one answered
Well, you could argue that energy flows in the vacuum and the drift of electrons in the wire are just a consequence of the fields created by that energy flow. Wiring is just shaping that field, and the electron flow is a side effect.
I'll have to study all these video's to see how it stacks up to what I've been taught and also to adequately know what everyone is posing. Fortunately the subject at hand doesn't make any difference to current carrying capacity as we know it, but is interesting as I have been taught differing things throughout my life. 43 years ago 1980 at high school everything current, field, electron flow all went at the speed of light. As an Electrical technician doing a physics refresher course over a year in 2008 to keep the brain cells firing we were taught the electrical field is created at the speed of light but the electrons themselves move in a sporadic motion as they bounce and collide with atoms in the whole conductor and as such the actual distance travelled along the conductor is very low with out getting into differing variables, voltages etc. I'll have to watch the the original video in question but was confused when Cathy brought static electricity into the video. I love your video's Cathy they are a real treasure.
Every circuit has both capacitance and inductance as well as resistance. There's an RC time constant and an RL time constant. It's easy to work out if you know the values of R L and C
Thank you for the video, I unsubbed from Veritasium because Derrick lacks Veritas - he writes too much clickbait, which we already have way too much of.
Your take on Feynman and his quote is totally incorrect. Feynman is not saying that you can't explain physics to dumb people, Feynman is saying that he wont dumb physics down for people. Einstein had a similar quote, something to the effect of "make things as simple as possible, but no simpler." You should consider the consequences of using a position of authority to convince people that they understand something when they actually don't.
Overall, I found your video very good in that you present your argument with references without being attached to your view which we can comment on. But I think you're wrong in parts: At the start of Derek's video, he says: "now you have to make certain simplifying assumptions about this circuit..." so listening between his words, I would still go with (d) 1/c; because to me, it looked simple enough to be modelled as a transmission line. Note he did a follow up video 'How Electricity Actually Works' confirming this, and showing the waveform of the pulses; where current clearly initially flows into the characteristic impedance of the transmission line, and lighting the bulb at a level lower compared to the DC steady state: but it still lights the bulb. Voltage, energy density and the Poynting vector are physically meaningless locally, needing to be evaluated between two points, integrated inside a volume, integrated over a closed surface area respectively to give physically meaningful quantities. So the Poynting vector is mathematically consistent for DC circuits, so long as you don't try to create a physical picture on how it behaves locally, and stick with integrating it over a closed surface area to get the rate at which EM energy is crossing this closed surface. Also, the Poynting vector is part of the EM conservation of energy theorem derived from Maxwell's equations via the assumption that J.E = the rate at which work is done by currents and the electric field interacting with one another. It's also derived more elegantly from the Lagrangian for electromagnetism.
I thought this pinned comment could be a good place for people to add (respectfully) things in history and physics that you think I made mistakes on or need more clarification. Please nothing about sound quality or other superficials in this thread. Let me start: I wish I had added that when a battery is in a circuit the chemicals take a while to react, so that the electric potential difference from the charge distribution Delta V is less than the emf, or the chemical potential energy per charge. The equation becomes Delta V = emf - ir, where i is the current and "r" is the internal resistance. This is why a battery heats up when you have a lot of current flowing through it. 11
I sent you by email the PDF of a highly relevant paper on the very subject (Galilia and Goihbarg, 2005). You did not use it. Have you got it?
BTW, I also think you misstated something about Feynman because you first agree with him and then seem you say that the same quote is nonsense. I've made a separate comment on that.
I'm currently working on a video debunking his video about the direct downwind faster than wind cart powered only by wind. I was going to do do a video about the DC electricity video. To me this two are very similar and both have to do with understanding what energy is and the fact that energy storage is as important as friction in physics but much less disused.
My simplification of Derk's DC setup will be using a charged capacitor instead of the DC battery and a discharge capacitor instead of the light bulb. I used this analogy and people have a hard time understanding why after the switch is closed assuming the two capacitors are identical just one fully charged and one fully discharged why only half of the energy will be in the two capacitors as half was lost as heat in the wire then radiated from the wire to the outside.
And yes the switch is a capacitor and you can transfer energy to the light bulb by only moving the contacts closer to each other without closing the switch so mechanical energy used to move the switch contacts will get dissipated as heat including in the bulb filament but no energy has left the battery if you return the switch contacts to the original distance.
The energy required to charge 30, 000 KMs of conductor, seems to be the limiting factor till quantified, the problem can continue being solved from there.
Quantum is a synonym of the word magic, it only remains so till explained using correct nomenclature rather than ambiguous bucket-terms.
Why do you jump from one name to other, then continually admitting you did not understand, did not learn it and you disagree. Your only credentials is that you showed up in the class and looked at many science cartoons. Fineman put science on the map, what have you done?
A worked example with known values would have been a good way to round off the video I think.
AlphaPhoenix actually tried to do Derek's experiment practically titled "I bought 1000 meters of wire to settle a physics debate"
Alpha's video proved, (in my view) that a transmission line is not the same thing as power supply. If the wires coming from the battery were perpendicular to the wires supplying the "bulb", you wouldn't even see much of a spike. And in any case you would not see continuous power.
Yes, his videos are very interesting, including the recent ones where he measured and visualised the "waves" of voltage propagating down the wire.
@@zhoufang996that video of Voltage waves is totally amazing and stunning. It truly makes the behavior of Voltage look like water. I'm a student in Electrical Engineering and I can't stop thinking about that freaking video.
And did an amazing job showing precisely how veritasium's argument is nonsensical
We know
Excellent comment, Kelly, you have pull this out of my lips - “real science makes you think and pseudo science makes you obey”.
Thank you
When I was studying Electrical Engineering in the early 1960's we first studied DC and Steady State AC circuits at lower frequencies. Then later we took a class in Transient Circuits and that introduced the concepts of electromagnetic waves and high speed transient effects of electrical conductors, spacing, conductor geometry, electric fields, magnetic fields and high frequency effects on circuits. Then we studied transmission lines, waves and antennas which then lead to Smith Charts and impedance matching and wave lengths, etc. I think what got Vertasium confused was conflating the 'transient' charge effects with the 'steady state' current/energy flow. Certainly an oscilloscope will see a 'pulse' of electric charge after the switch is closed but the light bulb required steady flow of electrons to create an (I^2 x R) energy flow to heat the filament and then create the light energy. Those two events don't happen at the same time. If all we wanted was to create an electromagnetic pulse then our house wiring could use hollow copper wires or 'wave guides' as microwave antennas us to move electromagnetic pulses around the house. However we need electrical energy to continuously flow to light bulbs and move motors, etc. so we must use 12 Gauge wire to move 20 amperes of current in a continuous manner to move energy without overheating the wire as the National Electric Code requires for all houses. The center of the wire as well as the outer part of wire all matter when you are transmitting DC or 60 Hz AC current flow to light bulbs, appliances, motors, etc. Of course if you are transmitting megahertz frequency signals to an antenna then the rules change but that is a different matter as I studied in college. Thanks Kathy for helping clear up the differences in electrical concepts of current flow.
The only difference between AC and DC is whether the current flows through the valence electrons or the conduction band. While the conduction band is closer to the heart of the molecule it is not the "center of the conductor". It is not like the "flow of water in a pipe" that's a blatantly false analogy. Electron drift is from negative to positive. The flow of current is from positive to negative. In the opposite direction. The charge is a virtual photon that pops in and out of existence as the electrons oscillate up and down their respective bands of energy. Most importantly the charge flows in the "holes" left behind the electrons. Not through or in the electrons themselves. That's why plasma physics requires ion's with electron-hole pairs.
@@calinbeale2634i think what everyone keeps getting at is "skin effect" which is frequency dependent depth of conduction. high frequency signaling results in charge density nearer the wire surface.
the switch closure could be considered an impulse, which is all frequencies but the initial edge will likely be the high frequency portion exhibiting the skin effect followed by the quiescent dc state. when you look at the voltage signal on the wavefront it's a step function... high frequency initially followed by zero so the depth of interaction should be increasing with time.
i would posit both components will raise the filament temperature. but the DC component will result in vastly more power dissipation, which makes the light.
I think Derek's imaginary circuit should have had two switches, one on each side of the battery terminals and closes the 2 switches simultaneously to see when the light bulb lights up? Of course, oscilloscope probes place after each switch, may be Veritasium just published the videos for the views only!
@@calinbeale2634 I was under the impression that valence electrons in a metal are already delocalized into a conduction band and that it is these delocalized electrons that are available to flow in a metal wire, either in a consistent direction under a DC electromotive force or in alternating directions under an AC electromotive force. At low frequencies, such as those used in utility grid transmission, I don't believe there is a distinction between the transport mechanisms for electrons through a metal conductor for AC relative to DC. At higher frequencies, we have to consider skin effect, but even then, I believe it is the same "sea" of delocalized electrons that makes conduction possible.
@gracenotes5379 the one thing I would add is that it is not just the conduction band. The CB is a shell for electron orbital closer in to the molecule. The valance band is a lower energy electron band where the "free" electrons float in a cloud. The electron oscillates between these two shells. When it goes up a band it's because it accepted a virtual photon and gained energy. If it goes down a band than it gives off the photon losing energy. It is the passing of virtual photons that is the electromagnetic wave.
I was one of those electrical engineers that reacted to Veritasium's video in a manner that can be best described as "wait a minute, that explains nothing".
It's true that an electromagnetic wave needs no conductor, but DC current most certainly does.
A lot of debunking of this has been going on since, and lots of good ones at that, so i won't go in to more detail here, but just saying that an explanation with the transmission-line model would have made perfect sense, and that the DC (battery) was a really bad example.
I can see that you have been thinking both long and hard about this, and your result is excellent!
What bugged me most about Veritasium's claim was the headline "electricity doesn't flow in the wire", well how else can you explain DC current?
I'm really looking forward to more of your video's since i find that the historic connection is giving me a firm foothold of understanding, it makes me more grounded, so to speak. (pun intended) :-).
Energy doesn't flow in the wire...
Another EE here. Yes I agree the transmission line model would clarify a lot, and it would explain that the light-bulb mostly likely will slowly ramp up in steps, as you see the reflected wave going back and forth between battery and light, that each have a different impedance than the characteristic impedance of the wire pair. If you look with a scope at the end of a not-terminated T-line you see exactly that. However, the pointing vector does work, even in electrostatics. I applied it myself when I wrote a field simulator (MOM based) to calculate the energy transfer. In this case you need to integrate the pointing vector over a closed surface surrounding the battery or the lightbulb. Voltage is only defined in electro-statics, and doesn’t work well if you have changing magnetic field. When we define voltage for an AC circuit, we use a quasi-static approximation.
Nobody seems to realize that these wire pairs are in fact a networks of resistors and capacitors (transmission lines). Dave and Electroboom get it. But I think this video and Derek's video don't seem to understand it.
@@kriswillems5661 I think Kathy said she had a graduate degree in electrical engineering. If so, she definitely knows what a transmission line is. BTW, you forgot inductor. 😛
@@kriswillems5661Kathy mentions dc circuits, and steady states, but in my non-qualified opinion, the fundamental thing here that closing the switch on this battery / wire / lamp situation creates, for at least an instant, a non-steady state between the two steady states of off and on, and for that intermediate instant this arrangement behaves as an AC system, which is why transmission line theory explains what is going on. Overhead HV transmission lines have a capacitance to ground of several nF/KM, this experiment doesn’t need a light-second’s length of wires to illustrate, electricity leaking away in an AC distribution line is well understood.
Kathy is electrifying and totally awesome! No shock there. She illuminates this topic beautifully. ❤🎉😊
Yeah this video is great. I wish I had science educators teaching me when I was in shool that were half as good as Kathy is at talking about this.
@@WarrenPostma so if we have perfect circle od wire (length 300 000 km, diameter 95541 km ) and we push the switch, will that signal travel just one second ?
Three sentences: Three puns. Three grΩns.
She's a bright spark.
This comment has a high potential to be punny.
Alpha Phoenix just posted a video where he measured voltage at multiple points along a wire. His animation of those voltages wonderfully shows the flow of electricity through a wire after a switch is closed.
Incredible video!
Thank you, that was exactly the video I was thinking about when I posted my comment above about transmission lines. The theory is very well established.
@@philkarn1761which video
This video and Alpha Phoenix's helped me understand the topic. Derek OTOH seemed to try to "bewilder and amaze", for the view count.
@@webherringSadly Derek has become a shill capitalizing on sensationalism.
This is the peer review process in action. Love it.
No, this wasn't equivalent to peer review, this was equivalent to response papers. Peer review works very badly compared to replications.
@@laurenpinschannelsobviously the veritasium video is already out there. I think this IS an actual example of peer review, in the same way that a response paper would be a form of peer review in the general sense of the phrase.
It is just an example of people creating controversy out of nothing.
In order for there to be peer review, the reviewer must address the subject under discuusion, in this case the Poynting vector. All Kathy does is to profess a dislike for it and for David Jackson who includes a discussion in his book. Kathy claims to be a physicist, but seems unaware of the Poynting vector until the present discussion. I was introduced in my junior E&M course and saw it again in graduate school. The Poynting theorem is simply derived by dotting the E vector into Ampere"s Law and then rearranging to form a conservation law for electric energy. The Poynting vector certainly describes the flow of EM energy through empty space. What is needed here is a discssion of the Poynting vector in dc circuits. Kathy throws up a lot of irrelevant facts but never gets around to the real issue. She does make a glaring error by saying the the electric field is the (negative) gradient of the poential, which is only true in electrostatics. In electrodynamics, one must also have a vector potential to account for the unconservative nature of the electric field due to Faraday's law.
Part II about Feynman: I believe that he was speaking to religious zealots and other crackpots who are eternal science deniers. He was NOT claiming that you can't explain things to children. I do think you have misinterpreted his words.
in fact feynman was great at breaking things down and simplifying in order to explain them.
He just was opposed to saying that the simplified way is how it works.
When you simplify something in order to explain it, you should say that it's simplified.
@@tommihommi1 I totally agree, that is the point of the Feynman diagrams and the "shut up and calculate" statement, he was always trying to show that the world is strange and wonderful and how things work as opposed to how we understand things work as they can often be mutually exclusive and that is what science is about teasing those two things apart to see what is real.
@Weirdly_wonderful I think I agree with the other commenters, here, about your take on Feynman's quotes which you said were about "education." I don't view the segment that you used about education or about speaking as "handed down from on high," the way you seem to be suggesting in your video. The clip you used was from the beginning of his 1979 University of Auckland lectures describing the theory of quantum electrodynamics (for which he and others shared the Nobel prize).
When viewed in the rest of the context of that video (and especially that segment of his first lecture in the series), my interpretation of what Feynman was describing in that quoted section of video was "I am not going to make a fake analogy to give you some false impression about how this theory works, but because of how crazy the calculations look, or how strange the conception of the models may seem, you may not accept the conclusions we get to draw from this model and conception of how nature works. If you don't like that, you're either welcome to move to another universe where the rules are simpler, or try your hardest to come up with a different explanation and conception that fits what we've observed."
In my view, this just expresses Feynman's personality and general commitment to not taking shortcuts in trying to give explanations for how things work (according to "the human beings who have struggled as hard as they can to understand it"). He says he can't make it simpler, because at that time (and as far as I know, even now) we don't have a simpler conception of how nature works, at that level (explaining quantum electrodynamics). But in my view, it is not a general remark he is making about explaining all of physics or a general remark about the nature of education. Would you agree with that?
Totally agree. Wasn't it Feynman that said "if you can't explain it to a child, then you don't understand it yourself" (or something to that effect)?
So no, I don't agree with Kathy in her view on Feynman.
ps. Seems like it's a quote by Einstein... maybe I just remembered it spoken by Feynman...
Love these videos!. Earlier today, AlphaPhoenix put out a video called "Watch electricity hit a fork in the road at half a billion frames per second" with some interesting observations and visualizations on DC electricity.
That sounds amazing
Funny, I saw alphaPhoenix' video just be for this one.
I just watched about half of the AlphaPhoenix video. He talks more about the flow of information than anything else. That is all pseudo science.
@@davidhomer78because he gives you all the information to follow the scientific method and repat his findings, it wouldn't be pseudo science.
@@Kathy_Loves_Physics It is wonderful. I get lost in the technical explanations, so I'm not sure Alpha Phoenix's video is directly or tangentially relevant to Derrick's video or not, but it seems so.
Eric L Michelsen touched the right point. I suggest reading Oleg D. Jefimenko’s Electricity and Magnetism, topic 9-5. Displacement Field and Static Charge in Current-Carrying Conductors for clarifications about the static fields in conductors when steady current densities are present.
Jackson’s 1996 paper indicates this when saying: “With the early notable exception of Jefimenko’s book, intermediate or advanced texts are no better”.
This is a very useful comment. Thank you.
Thanks for your interest, Gianmario.
Veritasium is often off the wall and somewhere out in left field for fake shock effects. People in YT just to grab a mega audience and make money doing so. You rock, Kathy. The truth wins.
Another very good response to Veritasium's videos. One of Derek's reasons to make the original video was to spark discussion.
I think you misinterpretted Richard Feyman's comment about keeping it simple.
Einstein once said "God does not play dice" The response was "Eistein, you cannot tell God how to make the rules".
One of Feynman's strengths was, "if at first you don't understand what you are looking at, then don't say physics doesn't make sense. Try looking at it differently till it does ".
You confused me when you first present Feynman as rejecting the Poynting vector theory, but then state that you reject Feynman's material on the Poynting vector. After checking the Feynman text in its proper context, I noticed that he gives further explanations why it "isn't so terribly puzzling" after all, with the right way of looking at it.
Btw, in the "go somewhere else" video Feynman was NOT saying that some people may just be too dumb to learn physics. He is just criticizing people who have decided to reject stuff like quantum mechanics and relativity because it is "too crazy". Feynman's reply is that if you don't like this crazy stuff, go to a universe where the rules are simpler.
And it mystifies me why you should even consider discounting the physics work of Feynman just because you (falsely) believe you disagree with him on a point of pedagogy.
All in all, this video does not paint you in a very good light at all.
If you listen to Feynman he actually says that the theory (Poynting vector for energy flow radially into a DC carrying wire, etc.) is correct. He further says that our intuition does not match the theory but this is ok.
Poynting (1884) shows that the energy (per unit time) flowing radially into the wire is actually the same as the power given by the much simpler, V*I. V*I is just much easier to calculate than the Poynting vector but it doesn't say anything about where the energy comes from (the E and B fields).
All electromagnetic theory has to be expressed in terms of fields, the 'flow of electrons' is just a sideline. A full treatment would of course use Quantum Electrodynamics whuch brings us back to Feynman 😁
(Melrose's Quantum Plasmadynamics, may be a better jumping off point for someone interested enough to do the full calculation or at least draw the Feynman diagrams).
I've looked at almost all the comments. It seems Kathy doesn't want to respond to critiques that the Poynting vector is correct for DC circuits. She took Feynman out of context. Her rationales for not trusting the Poynting theorem are not strong enough and don't stand up to scrutiny.
Kathy. I just found your videos. I like learning from passionate women and I like your teaching style. Many thanks.
Well, I made some work about Poynting vector especially in quasi-static cases (in the circuit frame). According to me, there is nothing wrong with the present theories, only a poor understanding of the Poynting theorem I am afraid.
The Poynting theorem doesn't say anything about the actual flow of electrical energy. Worse it gives infinite possibilities to define the energy flow through a vector field, all leading to the same balance. I have shown in one of my articles (published in the AFLB journal), that you may define an energy flow in a capacitor not going outside radially but axially (parallel to the wires) as your intuition suggest, with the same overall balance.
More technically, you can add any rotational field to the Poynting vector without modifying the energy balance. Discussing where the energy flows from one point to another point is pointless :-) both in Maxwell frame and in the QED frame (In the quantum frame, the trajectory of a photon is not more defined).
You may consider the flow of energy in the wire, or outside it like Derek and many others, or in circles as Feynman introduced in its course to illustrate the idea of the indetermination of the energy flow (you should have followed the entire course instead of extracting only a short portion of it !).
If people generally use the cross product definition it is because it is clearer to describe waves propagation in vacuum, and also because its a relativistic invariant, but this is another problem we may discuss another day. The philosophical question about the actual path of electrical energy flow remains open I am afraid !
Thanks; I was very confused by the Veritasium video which I was never able to digest. AlphaPhoenix just posted a series of videos that made much more sense in which he modeled charge as waves as it moves through wires. It struck me as logical and well presented, and so is a strong recommend.
I have to go with science, which is why I assiduously follow your channel. You're a hero.
Yeah - there is just one problem. Shinola gets 20Million views and a $100K check from youtube. Science gets 2000 views and lucky if it gets to million.
That's why I don't view the crank channels. Arvin Ash and Sabine are straight-shooters.@@joeboxter3635
@@joeboxter3635true
I think Feynman's quote to be one not about education but one about the scientific community. I like this take quite a lot. To me it's in the same vein as Tyson's "The universe is under no obligation to make sense to you"
Tyson certainly has never made sense of it.
Agree. Feynman was very much in favor of education and explaining and there is much evidence for that view. Here he is pointing out that he's going to be brutally honest in giving an explanation and won't oversimplify it for the listener, which would be dishonest. He says the same when explaining quantum mechanics of light. I love your history lessons Kathy !
Feynman was an elite teacher. He wanted people to understand the concept, not just accept it because a bigshot scientist told them so.
@@fotrj No, he wanted people to accept the concepts of modern physics even if those concepts go against our intuition. If some lay person tells him "time dilation is absurd, your math must be wrong, come back with something better", then he will tell that person to go somewhere else.
I thought seriously. about creating lots of new accounts so I could like this video a bunch more times... Kathy, thank you so much, I still have tears on my face because of your kindness and humility, not to mention all of your hard work.
Have you seen AlphaPhoenix's recent video? Especially his second channel further explanations about impedence matching? I find it a great explanation as well.
I'm Eric L Michelsen, but Google is scrambling my name. To clarify, I'm affiliated with the University of California, San Diego (and my last name is spelled "...sen"). There is much interesting and useful material in this video. For example, I have given a talk describing simple experiments which show that power does NOT flow along the Poynting vector, and that is fully compatible with electromagnetic theory. For reference (but not claiming infallibility), I have a BSEE, and a PhD in physics, and decades of experience in laboratories and measurements; I teach this material at the upper-division college level.
However, I think it is well established that the electric field inside a current carrying wire does, indeed, drive the current, and that this field is created by surface charges. Conductors can expel E-fields only in a static (or quasi-static) system. In contrast, a DC circuit is a steady-state dynamic equilibrium, and though the charges in the conductor move to reduce the E-field, the battery is constantly "pulling" them out of (and "pushing" them in) the wire, so they can never cancel the E-field completely. It takes only a tiny E-field in a good conductor to drive a significant current. This is established by extensive experiment, and organized into the detailed theory of electromagnetism (with no deference to anyone's authority).
I have a detailed discussion of the speed of electricity and the Poynting vector in my "Funky Electromagnetic Concepts" (at the bottom of my web page), starting around page 69 (as of this writing). I performed (the moral equivalent of) Derek's experiment, and confirmed that in some very realistic situations (but not all situations), the bulb turns on nearly full brightness, nearly instantly (as expected from theory). My document includes photographs of my setup and results, and a discussion of the theory, but is written at the upper-division college-physics level. This is all well-established science, and fully consistent with relativity. (In Dr. Muller's follow-up video, I think he actually didn't give himself enough credit for his prediction.)
Could you please give us a link to your website?
google for: eric's physics web page
When you close the switch, positive charges start to spread on the plus pole, and negative charges start to spread on the negative pole. These charges cause on electric field. On the positive side, with the positive charges, the field pushes away positive charges in the parallel wire, on the negative side the field pushes negative charges away in the parallel wire. So an unbalance is created in the parallel wire and a current flows and the light goes on. This happens after 1/c seconds, because the field only need to travel 1 meter. It's pretty simple, both wire pairs act as capacitors. And DC pulse passes the capacitors (but a continuous DC voltage does not). The continuous flow of current happens only later when the electron flow in the wire starts. This happens much later. So, the bulb flashes after 1/c seconds, but it is only stable much later on.
Your videos are very informative. Please keep posting on regular basis.
Love the actual experiments you’ve done! Great channel that I have frequently used before giving lectures to give some human interest to where these equations come from in the first place. Great book too!
...and I think I can reconcile two of my favorite science educators in my mind. Feynman frequently tried to be dramatic in order to engage his listeners and at heart is a theoretical physicist. Kathy is, at heart, a teacher, and to you, it is the teaching and communicating. Feynman wants the student to already have a complete grasp deep within maths. Kathy, is happy to explain in simpler terms. I like Feynman. I love Kathy. I have Feynman's lectures. I watch and re-watch Kathy's TH-cam stuff to refresh my mind and reeducate myself for all the stuff I forget or forgot. Thank you, Kathy, for making me very happy. Thank you, Richard, for your contributions to science, too.
Exactly. They're really in violent agreement here.
Feynman is happy to explain physics. He does that in his lectures. But he will (very obviously) refuse to bend physics just for the sake of people who reject concepts that contradict their intuition. That was his whole point. It had nothing to do with how to teach physics. Kathy misunderstands Feynman completely on this point.
@@ronald3836 Exactly.
Can't believe we are equating a TH-cam creator to Feynman. It's just laughable.
@@CMHandle That's unfair. Everybody has their contribution to make to education.
What Feynman was saying is that the universe has no need to be simple ---in terms of linear, intuitive to human understanding etc---and that one must accept experimental evidence over a neat simple concise but wrong theory. In terms of his views on education, there were two main sentiments expressed:
1) If you can express something in a way that ordinary people can understand,,then the likelihood is that you don't understand it as well as you think (that's his famous meme on learning)
2) Somethings in nature cannot be explained without first explaining a whole gamut of mathematics except by analogy.
The second sentiment was expressed in an interview where the interviewer had asked him to explain how magnets work and why. Feynman could go only so far before he needed to upgrade the individuals maths skills.
I think that your notion is entirely true in that: anyone should in theory be able to understand anything scientific; however, the depth of understanding does depend upon having or possessing mathematical ideas once you go beyond certain levels of knowledge.
I'm sorry but that's really not how batteries work.
All chemical cells are based on specific redox reactions occurring within them. Some of these do use acids or bases and metal electrodes as their reagents but others do not. Their common element is that half of the reaction (reduction, which consumes electrons) occurs on one electrode and the other half (oxidation, which generates electrons) occurs on the other electrode.
The simplest cells will achieve this by making the electrodes from the reagents, but _there are_ plenty of cases where one, or both electrodes take no part in the reaction. You can keep the electrodes in two different solutions connected via some sort of an ion exchanger. You can cover the electrodes with a catalyst. There are plenty of options.
And second of all, when the battery is not yet part of the circuit, the reaction indeed isn't occurring. But that doesn't mean it can't give you current right away - as soon as you complete the circuit. The reaction isn't progressing precisely because it has progressed the furthest it could get, building up charge on the electrodes, internal wires and the terminals.
And finally, the heat generated from resistance is frankly negligible. The vast majority of heat will be produced in the chemical reaction itself.
The electric field inside a wire is only zero when there is no current in it. If it's carrying a current and it has resistance, there will be a charge gradient along it and therefore an electric field.
Awesome channel. Perfect balance between accuracy, sources worth learning more from, and an engaging presentation. Chapeau!
The fact that people are STILL posting responses to that video gives me faith in humanity. I watch them all and every one teaches me something new, a slightly different perspective for thinking of how electricity works. Great one from Kathy here, with an illuminating historical perspective. For all the problems of that original video, hats off to Derek for pushing many of us to look beyond the elementary school depictions of electricity.
I am a BSChE about ready to retire in 15 mos. Going back to my alma mater to get a degree in physics. Been watching MIT OCW (diff eq to refresh after 40 years) and Elliot and ViaScience... and you... and some others but your videos are fantastic. Thanks Kathy!!!
I admire your videos. But now, i'm in love into them. You're great communicator and reinventor of old wonders and stories. Thank you for the great work. Looking forward to more videos
I think energy is just an accounting thing in physics. Energy is defined as the ability of a system to do work. If a system do work then its energy is decreasing, and the energy increases on the other system that the work is done on. This continues until both systems are in equilibrium and neither system can do any work on the other. The physical thing here is work and not energy. Like in accounting, my work is the physical thing and the money I get for it is just an abstract accounting number. So energy doesn't really "flow" as in something physical like water flowing in a river. Something physical must do work. "Energy doesn't flow in wires" is really nonsense, energy doesn't flow. What happens is that a field is created, that field is doing work, pushing the charges, those charges collide with other charges, change the orbitals in the bulb, those orbitals decay releasing a photon (which is also work) and the light bulb lights up. Mass as a form energy comes also from work done. About 99% of mass comes from the complex interactions of quarks and gluons in the proton, which is work. 1% of mass comes from the interaction with the Higgs field, which is also work.
It feels like you are taking Feynman’s comments on the Poynting vector out of context. The Poynting vector is a measure of energy flux, and that’s by definition, there isn’t anything to argue about there. What he was talking about is a bar magnet next to a battery, where no power is either provided or dissipated, but the Poynting vector is non zero, seemingly indicating that energy is flowing in circles, which is not intuitive, but is still true. To say that the Poynting vector doesn’t work at DC, or that it isn’t accurate is wrong, it works because it is defined to work, it is an extension of Maxwell’s equations.
I think this wholly comes down to semantics and what it means to "light up" the bulb. It also seems to have some relationship with the difference between the maximum speed of causality and the propagation speed of "meaningful" events in the physical world.
Actually, as you well know, Feynman did a a great deal to make physics understandable to people. Who is perfect across all areas at all times in their life.
Right. I don't get the anti-Feynmann slant in this video here, it's quixotic and unexplained.
Honestly, I don’t understand your confusion. I don’t think it’s good for someone to put something that they think is obviously nuts and crazy in a textbook.
Also, I do not know that he did “a great deal to make physics understandable to people”, as I’ve never seen a single example of that.
I’m not asking for perfection, I’m asking for kindness. But I have not watched/ read everything that he did. Maybe he was kind and relatable in other areas. I just haven’t seen them.
Also, we are allowed to have different opinions. I’m allowed to think negative thoughts about Feynman and still be a physicist right?
@@Kathy_Loves_Physics absence of evidence is not evidence of absence. Seeing involves looking. Maybe you have a responsibility to investigate properly, as you do for the characters you write about, before making such a public statement. Feynman did not have the attitude you claim, quite the reverse. Disappointed.
Warren, I am particularly interested in your use of the word quixotic. Quixotic is a reference to one of my favorite novels Don Quixote where a poor farmer decides that he is a knight, and a windmill is a dragon that he cannot defeat.
But I don’t get what that means in reference to my video. I mean, you could be saying that I am not really a physicist, just as Don Quiote was not really a knight. But if that’s the case, then my complaints about Richard Feman are quixotic means that Richard Feinman wasn’t a physicist either, he’s just a windmill.
Care to clarify?
It is hard to separate what Feynman did and what he claimed he did. The guy was an extremely good story teller and had a sizeable ego. That and he had a very poor attitude towards women. Kathy has every right to be suspicious of him, I can only imagine the amount of sexism she has put up with in this field.
I agree fully with Feynman's statement. My interpretation of it, based on some wider context, is that he saw simplification as inherently untruthful. He was well documented happily spoon-feeding complex topics to any level of audience. The important semantic detail is that simplification of a complex thing is an arbitrary modification of the thing, and not equal to dividing the thing into manageable components for learning.
Simplifications taught to children are very often a major source of trouble later in their education, and even in general life, because you have constructed a faulty foundation and now the entre first floor needs a complete tear down and rebuild before the second floor can be added. (This applies to any introduction level education, not limited to children.)
In short incomplete (building blocks) and incorrect (simplified) are different things.
You said, "It was because of Feynmann's comments on education that I started discounting all of Feynmann work." This betrays a fundamental principle of science that we look at the science, not the source.
Anti-scientists use this technique. "Oh, he believes in climate change, so I won't take his studies in geology seriously." Feynmann's improtant physics work was peer reviewed. So, you are also discounting peer reviewed science, including I suppose quantum electrodynamics.
I also have to point out that the lecture you showed a clip of was Feynmann at a QED lecture. The audience would be expected to understand his point. Facts (and observations) are the proper test of theory. It was completely irrelevant as to education of children. So, clearly taken out of context.
Real context: In April 1966, Feynman delivered an address to the National Science Teachers Association, in which he suggested how students could be made to think like scientists, be open-minded, curious, and especially, to doubt. (From Wikipedia)
Well, people often make the mistake of confusing the message with the messenger. It's actually a logical fallacy. If you want to attack an argument, attack the argument - not the one who is putting it forward. However, confusing ideology with how the world actually works is often producing this result. Which is a pity, because by very nature any ideology is internally inconsistent.
I love these historical perspectives!
Much of modern science communication is so difficult exactly because it is unaware of the original progression of discoveries that made us understand these processes in the first place.
I think we should teach most topics by repeating the original discovery, with newer information only added in where they really make it easier to understand.
5:59 Wait: "static charges don't affect field in the conductor" is only true if there is no electric flow. Imagine a battery short-circuited with a wire from + to -. Now draw a closed loop through the battery and the wire. Along the wire, inside the wire, voltage goes from +1.5 V to zero, therefore there *must* be a field inside the wire too. Charges are constantly moving in an effort to balance out this field, but can't because of the external (chemical) energy source.
I think a static charge means there is no electrical flow.
@@supermikeb yes exactly. Kathy is citing the rule that applies when there is no flow, while Electroboom is talking about a situation where there is a flow, balanced by a resistivity.
With dc it's the electric field IN the wire that drive current and power IN wire and ac will be totally different. Sounds like you are correct. Great video. Thank you
5:57 "Static charges do not affect the electric field in a conductor"
That is *remarkably* false. What Michael faraday discovered and whats actually true is that the electric field inside a conductor in electrostatic equilibrium is Zero. The simple reason is that a conductor can be seen to a fair degree of accuracy as a material with free electrons in it, this means that if there was an electric field inside these would feel a force and therefore they would move and that wouldn't be electrostatic equilibrium.
For a conductor that's not in equilibrium this statement is completely false, in fact, for a conductor to not be at equilibrium there MUST be a force moving the electrons inside it. This is such a major mistake it undermines the credibility of the whole video, and not the only such mistake btw.
Yes - it's the confusion between electric statics and electric dynamics.
Very interesting video. I'm curious if you have seen Nick Lucid's "Science Asylum" video from about 4 years ago titled "Circuit Energy Doesn't Flow the Way You Think" and what your thoughts might be about it.
I'm only 1:15 in, but I love you already Kathy.
I am not a scientist, but when I first watched the video at Veritasium, I was deeply disappointed by his simplistic approach.
I am reminded of the fact that science progresses because good theories get replaced by better theories.
NOT because of bad theories being replaced by good ones.
It is a process I refer to as "Continual Refinement" and I try to apply that process to myself.
And of course we must understand that Kuhnian paradigm shifts take place in science, and how messy they can be, because science is performed by humans with big egos.
I think I miss something. You seem to agree with Feynman around 7:20 and 8:00 but then disagree with the same quotation around 10:15. What did I miss?
PS. The third instance of the Feynman quote (20:45) makes it even more obscure to me. What is pseudo-science here? Feynman's lecture or treating the Poynting vector as an energy flow for the case of DC currents?
Kathy is delusional here. What Poynting says is no word salad. Its 19th century physics terminology but perfectly correct.
And Feynman was wrong if he meant that "absurdity" literally. The "absurd circulating energy" form static electric fields and static magnetic fields has been measured. More specifically it predicts that there is momentum from this circulation and that momentum can be measured.
This is all far less "absurd" once you realize that a magnetic field in the classical picture requires charges to move. There is nothing "at rest" once you include magnetism.
@@michaelrenper796 I think Feynman means that this may be mathematically correct but is physically meaningless. If this is measurable, as you claim, he is wrong. Can you give me some quotes to this effect? Preferably to original scientific papers.
@@arctic_haze Can you quote a scientific paper that says the Poynting vector is physically meaningless?
You see! Go and search yourself.
@@michaelrenper796 OK, so I can forget all you said and stick to what Feynman taught (usually not a wrong choice) as you seem to have nothing to support this claim. And I almost believed you for a few minutes.
PS. I looked into the literature and although some papers claim that this Poynting vector interpretation is necessary to provide conservation of energy and momentum (not a big surprise), I could not find one claiming that this is actually measurable. Some even postulate using a "hidden momentum" to cancel out the Poynting one. As I said, total confusion.
I agree, I am confused too.
The Poynting vector itself does not represent energy flow. If you integrate the P. v. around a closed surface, the result is the net energy entering or leaving (depending on sign) the enclosed volume. Alternatively, the divergence of the Poynting vector indicates if a locality is sourcing or sinking electromagnetic energy.
Feynman was addressing the view that the vector itself represents energy flow.
But note that Feynman does agree with the theory which is "obviously nuts". His point is that the theory goes against our intution, but that does not make it wrong (and if you don't like it, then I guess he'd say you can go somewhere else).
Feynman also points out that the practical consequences are near zero, and I very much doubt that it has any real relevance to Derek's question. "Energy" is anyway mostly a bookkeeping device.
@@ronald3836There is this one experiment that you could theoretically do where you measure the gravitational field generated by the energy and energy flux distribution.
However carrying such experiment in a lab is beyond current technological capabilities and as far as I know no one has postulated a way to do it with astronomical observations.
This video was clearly convinced out of ignorance tho, she only ever appeals to intuition and doesn't provide any real argument against poyntings theorem being applicable in a physically meaningful way to DC circuits.
@@marcossidoruk8033 That would be a very interesting experiment indeed.
I guess "energy is just a bookkeeping device" might not sit so well with general relativity. But I do think it is correct to say that we can't help to think about physics in terms of abstractions which the universe itself does not necessarily care about. And of course that is why we do experiments to find out how far our abstractions can take us.
There are these videos about "gravity is not a force", but that presumes that the Newtonian notion of "force" is more than a very helpful abstraction.
Derek could've saved himself a lot of grief if he'd just used correct units.
1/c seconds doesn't make sense, it doesn't solve for time.
Without showing where the "1" comes from, the answer appears to be the inverse of c, regardless of the wires proximity.
In units, his answer is 1/(m/s)=m/s, a measure of speed.
If 1meter is used then m/(m/s)=s, a measure of time.
Great video!!
Im interested if the cucit, but instead treated like a large circle and not two paralell conductors (EMP travel at light speed.)
will this relate back to Cosinus to f ,and electrical motors?
"EMF pulse" makes the initial energy sound "fleeting" like a pulse is. It is not. This is the misconception. When that switch flips, the electricity - the voltage and current from the battery - turns on and stays on until the main electric current from the loop catches up with it and increases it further. I think this is the common issue that engineers & physicists have, because they think sure, there's an initial minuscule blip from the switch but it's inconsequential. They are wrong: it is consequential, and it's because our intuition of electricity flowing in wires is incorrect. Maybe a helpful abstraction most of the time, maybe, but incomplete and wrong even when talking about transmission.
I was confused for a minute by the initial Feynman quote about the Poynting vector being "obviously nuts" until later in the video when I realized that it was just a comment on how non-intuitive he thought it was, not that it was false or wrong. I think I understand the sentiment but still appreciate the Poynting vector myself since it is just combining the force vectors of the electric field & magnetic field.
A fantastic video. Well presented and very informative. I love the level of detail and how everything is explained. Great stuff! Thank you!
As a lay person I've noticed that no matter the subject, a lack of historical perspective can be fatal to clear thinking. I think anyone who wants to study a science needs to retrace the path of those that went before us. Thanks for applying that principle to physics.
I remember when his first video on this came out and there was a big reaction and discussion to it. I feel it was the perfect educator situation, since it forces someone to really start pondering how all of it works before they can even start to come to some conclusion of their own. In the end, the places where he was wrong seem mainly to be from oversimplifying for pedagogical reasons, and slips of wording that were wrong or make it debatable what was meant, all of which allow for misunderstanding (since I am sure Derek himself understands this, it is more a matter of presentation). It is great that even after all this time, people are still making responses to it, and getting people engaged with the details of how it all works.
Thanks Kathy! The world is round again!
I have several comments about this video:
1) Your excerpt from the Feynman lecture is taken out of context and misleading. Taken in context, it is clear that Feynman is saying that even though it is counter intuitive and seems crazy, the standard interpretation of the Poynting vector as the energy flux is correct: the energy flows through the fields in the space surrounding the wires.
2) Your use of the expression "direct current" confuses the concept of "direct current" with the concept of an electro-static (or electro quasi-static) system. "Direct current" means simply "current that flows in one direction" and colloquially does includes what happens when a switch is closed in a circuit consisting of a battery, wires, a light bulb, and switch connected in series. The two different "steady state" conditions of "switch open" and "Switch closed" are well described by setting all time derivatives in Maxwell's equations to 0 which is called the quasi-static approximation. For a system that changes in time, such as when a switch is closed, this is approximation is only valid if you are only interested in time scales much greater than l/c, where l is the physical size of the system and c is the speed of light. This requirement is not satisfied in the described problem.
3) Your a) dismissal of the "Poynting vector" for describing energy flow in DC circuits, b) your characterization of the physics of closing a switch in the described circuit as "DC" and implying that the physics of the transient is no different from the physics of the steady state, c) your misleading quotation of the excerpt from the Feynman lectures, d) your discussion of the Maxwell equations, and e) much of your discussion of the difference between science and pseudoscience taken together indicate a lack of understanding of the meaning of the Maxwell equations.
The Maxwell equations are set of 4 coupled partial differential equations which, when supplemented by the Lorenz force law, Newton's laws of motion, and appropriate description of the system understudy, including initial conditions, describes the time evolution of any electrical or electro-mechanical system for which effects due to quantum mechanics are not important. This is not controversial; the successful operation of all the electrical and electro-mechanical devises in our modern world attest to their correctness.
Poynting's theorem, which is also a partial differential equation, can be derived from the Maxwell equations; so if the Maxwell equations are correct (they are) and the manipulations used in the derivation are valid (they are) then Poynting's theorem is true. Poynting's theorem is derived and discussed in all sufficiently advanced textbooks on electro-magnetism. In my library, the derivation is presented not only the Feynman lectures, but also in "Classical Electrodynamics" JD Jackson, "Static and Dynamic Electricity" by Smythe, and two volumes ("The Classical Theory of Fields" and "Electrodynamics of Continuous Media") of the Course in theoretical Physics by Landau and Lifschitz. It is even derived two books that are not strictly speaking electrodynamics textbooks: the mathematics textbook "Methods of Theoretical Physics" by Morse and Feshbach and the engineering textbook "Electromechanical Dynamcs" by Woodson and Melcher.
There is no doubt that Poynting's theorem is true. The only possible controversy involves the interpretation of the terms its terms.
The question of energy conservation in classical electro-magetism is discussed at length in Sections 27-1 through 27-5 of the Commemorative Edition of the Feynman lectures on physics; Poynting's theorem (although not referred to as such) is Eq 27.13, and it is derived in Section 27-3, and the quote taken out of context in the video appears in section 27-5.
Contrary what is implied in the video, neither this discussion nor the derivations and discussions in the other textbooks appeal to authority for their justification; they all present mathematically rigorous derivations of Poynting's theorem from the Maxwell equations, supplemented by discussions of the interpretation of the quadratic terms in the theorem as the energy density of the electric field, the energy density of magnetic field, the rate of mechanical work performed, and the energy flux in the electromagnetic field.
Poynting's theorem is definitely correct, and its interpretation as implying that the energy density and energy flux in a electro-magnetic system are both distributed in the fields is a mathematcially consistent and correct description of electro-mechanical systems.
In the video you refer to the product of the charge and the electrical potential as the electrical energy. This equation is only true for static systems, and cannot in general be used to analyze a dynamic system such as closing a switch in an electrical circuit. Feynman shows that for electro-static systems the expression in terms of fields, when integrated over the entire system, gives the same numerical result as the volume integral of the product of the electric potential and the charge density, while also consistently describing the full dynamic (time varying) case.
For the present case, there is no mechanical motion (the wires are assumed to be stationary), so only electrical properties are important. Furthermore, the conductors are assumed to obey Ohm's law. In this case, if the geometry of the wires is specified, including the geometry of the switch, the Maxwell equations can be solved to determine the time delay between closing the switch and the light illuminating. Except in special cases, the equations cannot be solved analytically, but have to be solved numerically on a computer. This is well understood physics, and I assert that the chance of a disagreement between the results of the calculation and an experiment.
For the present case, the Maxwell Equations can be solved numerically to calculate the brightness of the bulb as function of time. This time dependence depends on the exact location of the wires, so your statement that the correct answer (if the question is interpreted as asking for the time it takes the brightness to settle down to the steady state value) cannot be determined from the statement of the problem is correct, but the strong implications that the validity of Poynting's theorem is controversial and that time dependence cannot be accurately computed using the Maxwell Equations is false.
In many cases intuitive understanding can lead to accurate and useful insight, although intuition is no substitute for detailed calculations. In the present case, my intuition says that a) electric current cannot start flowing in the bulb until enough time has elapsed for an electromagentic wave to propagate between the switch and the bulb, b) the steady state will not be established until a time somewhat longer than the time required for an electromagentic wave to propagate all the way around the wire, and c) the details depend on the exact geometry of the circuit.
Re Feynman, as a fellow New Yorker (but uh, not a fellow genius) I think he was just getting at there being a level of irreducible complexity where intuition cannot take you and you have to rely on the math, stated in kind of a sarcastic way. Its ok if you take issue with that, but I don’t think he was insulting children there, just that… like, if you want a 5 year old to understand the path integral formulation of quantum mechanics, the 5 year old will need to be a 6, 7, 8 , 10, 15, 20 year old that learns all the intervening math, and classical physics. Feynman is just saying he can’t do that work for you - thats my interpretation.
Has no one ever used an oscilloscope? A scope especially with storage will show the transients and provide an way to measure them. Modern scopes can go well over100MHz and can easily capture nanosecond events. It might also be interesting to use coax instead of bare wire.
Derek knew exactly what he was doing when he created this passionate debate, catering to the algorithm and justifying it for education.
A shill selling sensationalism? I’m shocked! /s
When I was in college, the professors acknowledged that the electrons flow from - to +, but to keep the math easier, we engineers cleverly came up with hole-flow theory... as an electron moves, it leave a gap, so the one behind that comes in to fill that spot, but it left a hole and the next one behind that moved to fill that gap, and so on. If you look at this gap, or "hole", it is moving from + to -, hence hole-flow theory.
As a Master Electrician and keen viewer of your videos, can you please tell me if you think electrons go forward and backwards in an ac circuit. If so, how far backwards and forward do they travel. I've looked in my text books and spoken to my associates, but no one has a definite proof. Please help , thank you . John M French.
I think veritasium video mixes two topics, the steady state and the EM pulse.
EM pulse: you have to treat it like a transmission line. It will move some electrons in the light bulb about 1/c seconds later, but not enough to light it up. Bulb will light up only after the signal will be able to "check" the continuity of the whole circuit (otherwise superluminal messaging would be possible).
Regarding the steady state, once all the oscillations of the initial EM pulse have been dampened out: to me it seems only a matter of modeling. The most common model is that of electrons pushed through wires. The moving charges then cause EM (static) fields as a consequence, and, curious coincidence, a Poynting vector appears. But, you could easily say that, lying the conductor in a certain way, you put some constraint on the shape of EM fields, which carry the energy and, as a curious coincidence, electrons in the conductor start to move. Either way, you can't have moving charges without fields and viceversa. Choose the model that fits best, especially, the one that is easier to apply.
Part 2. Feynman talking about CRAZY Poynting theory was not implying it was wrong but that it's crazy. He believes it correct and explains the unusual aspect of the theory in his lectures. He shows how Poynting Vector describes energy and field momentum.
It's always true in EM theory that energy is conserved LOCALLY.
There is a partial differental equation that applies to any POINT in any EM situation, in or out side wire. It relates energy density, work done on charges by fields or work done by fields on charges and the Poynting Vector energy flux through surface boundary of tiny infinitesimal volume. Very tiny volume because it's a differential equation and so a statement about what's happening at a point. This LOCAL energy conservation law is fundamental and this is the reason you need Poynting theory.
In the infinitesimal volume when work is being done and change in energy density, you will have an flow FLUX of energy across the boundary surface which is described by the Poynting Vector.
So that's why you need Poynting. It's so you can explain what you mean by local energy conservation - the relationship between energy density, work and energy flux.
Me again. So by integrating the Poynting Vector over the boundary surface you compute the flux of energy across the surface. The usual expression for the time averaged energy of a plane EM wave, that IS the magnitude of the Poynting Vector. The unit's of magnitude of the Poynting Vector is power over area, usually watts per square meter.
Those hand held devices that measure radiation in an area are measuring the magnitude of the Poynting Vector (usually units of mW/m^2)
Also what is called the Solar Constant, well that again is the magnitude of the Poynting Vector (unit's of kW/m^2)
Me again. Local energy conservation an objective fact of EM theory, Poynting vector is just consequence. What about the solar wind DC current, where is the energy - in the fields. It doesn't matter what type of bulb he had his point was the energy is in the fields and field nipped straight across to the bulb with a little bit of energy to set up a tiny current as well as traveling round the wire. Those surface charges and shielding, that's Gauss Law, electric statics. Shielding result of Laplace equation having unique and constant solution for constant boundary conditions. Where is the energy in capacitor, charges on plates energy in fields between plates. Energy is ALWAYS in the FIELDS.
ALL your videos are brilliant and thank you very much.
Yes I understand what you mean but you are confusing electric statics and E dynamics. As l say Laplace is statics. You will still be able to receive a phone call on your mobile even in a faraday cage no problem, that's E dynamics. The Skin Effect that's electric dynamics and is how you would shield from EM waves, it also like a limiting affect for heigher frequencies becoming like a faraday cage shielding.
Physics totally different tho, for statics solution of Laplace equation and for dynamics the differential is like the diffusion equation with time derivatives and solution similar, exponential factor, providing attenuation.
Yes I think you are correct tho. The point is this Poynting vector is mathematically correct but doesn't distinguish between kinetic and potential energy. For DC there will be current in the wire and energy flow inside the wire. The Poynting Theory HAS to be correct but it doesn't distinguish between kinetic & potential energy. I think that is the cause of confusion.
I really enjoyed this, and especially your insistence on positivity in the approach, it has given me a lot to think about.
I thought that in the condition where the bulb is very close to the switch that the bulb would light immediately, similar to the time it would take if the circuit were of small size rather than half way to the moon (or whatever the distance was). I assumed this based on the circuit would be in a steady state prior to closing the switch and there would be a difference of charge potential across the switch, and the charge in the wire on the long end would be constant along it's length. When the switch closes, current begins to flow immediately because of this difference in potential and as the current moves along the wire it continues to provide difference of potential as the charge from the far end of the long wire eventially catches up.
OK maybe I did a poor job of explaining that. It's late and I'm tired. It was fun to think about though.
And no, I don't recall any mention of Poynting Vectors during my education either.
All of your videos are a treasure
Bravo for summarizing the most important elements of disagreement before you even got to the table of contents.
I appreciate the time and effort you put into your videos, but my utmost appreciation is towards your tone. I love how measured and thoughtful your videos are. You make the topic very approachable for the newcomer, but also have enough detail and complexity for a well-rounded presentation. Your respectful response to his video is how such videos should be handled.
Albert Einstein is said to have stated “If you cannot explain your theory to a seven year old, you do not understand it yourself”. I agree that anyone can understand any of the concepts in science if they are properly and concisely presented. I enjoy the presentations on this channel because they are presented so.
Maybe Einstein wasn't right about that. But your later statement is patently false - there are scientific concepts that are outside the reach of some humans. This is true also for me, there are things in science I know I csnnot fully grasp.
Closing a switch to power a transmission line is sending a very frequency signal on a transmission line. The line will absorb the current matching its impedance until it reaches the end, where the power will be absorbed or reflected when the load resistance doesn't match line impedance, it will take a few iteration to stabilize and then the circuit can be called a DC circuit. The all argument is a misunderstanding about AC and DC.
Kathy, I bought your book and wow, so much good dope, kudos! I love history, and electronics has been a hobby of mine since 5th grade! I am self-taught in engineering, as I have no aptitude for a school environment, exams and drinking lectures as if from a fire hose.
Love this! Finally a "fight" with reason. I'm waiting for Derek's response :)
05:56 "static charges do not affect the electric field in the conductor"
You are so wrong that it hurts 😢.
Please do not mistake the electrostatic case with the quasistatic case of stationary and slowly varying currents. The surface charge (and in nonhomogeneous materials, the interface charge) does determine the electric field inside the conductor and that field is not zero. In fact, it has the value specified by Ohm's law in its local form.
Go read Sommerfeld, or solve the system of Maxwell's equations along with the costitutive equation and the equation of continuity to see it.
I love your videos, I used to have electronics as a teenage hobby and one of my uncles was working as a microwave electronics consultant in the 1970s here in Australia. I identify with all that you say. Lots of love from David Newton x
The timing on this video is perfect as Alpha Phoenix just released a video about a similar thing, but his explanation of what’s happening felt a bit lacking to me.
Thank you very much for doing these well researched video topics with a lot of thought experiments that have been invested in them. Keep this going and take care of yourself. Cheers.
I had the great misfortune of having to useJackson's Classical Electrodynamics book in my graduate classes in the 1970s. It was impenetrable then, and it''s impenetrable now. Like gravity, I think we still don't really understand EM.
I think it's a masterpiece. It's meant to be read chapter by chapter.
@@BarriosGroupieyeah, but so is the bible.. which reads about the same. Lol
First you agree with Feynman that Poynting's theory is nuts, then at 10:10 you say Feynman's "material on the Poynting vector is nonsense."
19:39 yes, I think that should be the goal, but sometimes it's impossible with modern physic, especially quantum mechanics. In this casecyou have to simplify and/or interpret things if you just use words. However you shouldn't go further with tjis then necessary.
You’re reminding me of how I learned about ignition coils in high school auto shop. The transformer in an arc welder demonstrates these principles.
This is great that we are finally having a discussion about this. I think people think that electricity is like water and flows in the pipes.
I give you 2 thumbs up! I don't really understand all things electric but I do have a great fascination with them. When I watched Derick's video on how long it would take to light a bulb I felt uneasy with his explanation although I wouldn't have been able to verbalize it. Your video helped my understanding of my original unease. I also greatly appreciate your definition and comparison of true science vs psudeo-science. Thanks for posting.
Hi Kathy. Do you have a vide for Fuel Cells History and Grooe Cell and about Sir William Robert Grove ?
Thank you once more, Kathy........just commenting to tweak the algorithm.
It was like engineers arguing with physicists.
In Electronics, we have a number of models and tools to design our gear including
conventional current which is opposite to conventional flow.
As a tech, I was first taught electron flow and regret it to this day.
It’s like learning imperial system instead of metric.
I learned about skin effect in AC but I see there’s a lot more to this than I realize even though
I really don’t need to know it for my daily tasks.
Socratic method of asking and answering questions to arrive at a truth…like the Paper Chase.
I enjoy the deep dive down the rabbit hole to Wonderland by all the creators on this subject.👍
I started as an electronics tech in the Marine Corps, and they taught electron flow. It seemed odd that current would flow against the arrow of a diode symbol. However, that was still the era when vacuum tubes were in use, so there is some sense to talking about electron flow. That school was pretty basic, and raised enough questions in my mind to motivate me to become an electronics engineer.
@@SkyhawkSteve There was... at least some... American profs writing textbooks using electron flow (versus conventional current flow)... but, AFAIK... and apparently... it never caught on. Eventually, I think, everybody promoting electron flow gave up trying to change it.
Electricity, Magnetism, Heat, light / Color, Mass / Weight are different manifestations of Gravity and Continually convert to each other. Gravitational Particles (GPs) move by means of CONDUCTIVITY towards the CENTER of the GRAVITY.
Turbines convert the Gravity Force to Magnetic > Electrical > Heat > Light and everything in between.
When GP moves in the Air (4N1O) Atoms are manifested as Magnetism, therefore Magnetism exists only in the Atmosphere and is absorbed by Compass measured in Air Gap and Magnetic Flux context.
When GP moves in Solid it is observed as Electricity and measured by its Power/Force/Voltage and its Current/Amps and their combination total Quantity of GPs in a unit of time as Wattage.
GPs move at a 90 Degrees Angle relative to their path in [side] Steps, therefore the GPs manifested as Electricity, Magnetism, Heat and Light transit to the Outer Edges of the Medium/Matter.
@@ShonMardani No.
No to what? @@willthecat3861
I disproved Veritasium with a very simple experiment: I put a _second_ light bulb right on top of the first bulb, but without connecting it to the battery. If the electrical energy flows through the air directly from the battery towards the bulbs, both should've lit up. But only the connected one did.
Derek did not respond or explain why the unconnected bulb did _not_ light up. To be fair, his video had already received tens of thousands of responses by then, and it was physically impossible for him to respond to every one of them.
I also pointed out that in computer networking, the network latency-the time it takes for electrical signals to travel from one computer to another-depends on the _length of the connecting wire,_ and not on the as-the-crow-flies distance between the computers. This fact is not in dispute. This is why the stock exchanges, for example, make sure that the networking cables connecting the exchange servers with the traders' servers are all of the same _length,_ so that all traders receive trade messages at exactly the same time-to the nanosecond.
AlphaPhoenix showed it also works with disconnected lines. How did you do the experiment? Because you need very sensitive equipment to actually measure this and a normal light bulp won't actually light up visualy.
@@drfisheye Oh, I'm not disputing that an electromagnetic pulse (EMP) spreads out from the switch-not the battery, BTW-when it is closed. No doubt, the EMP can be measured with sufficiently sensitive instruments. This EMP travels at the speed of light (in air) and jiggles the electrons and protons in all the objects it passes through, including the bulb, its filament, and its glass shell. In fact, as you pointed out, it's not even necessary for that bulb to be connected to the switch and battery for it to feel the EMP. The length of the wire is irrelevant-it's just a misdirection.
BTW, I'm an engineer and a licensed HAM, so I know my way around Maxwell's equations, electromagnetic waves, wireless transmitters and receivers, oscilloscopes etc. Of course, I'm not saying I understand everything-far from it. And while I use the Poynting Vector to calculate the power transmitted by an EM wave, I don't ever recall using it to calculate power transfer in an electrical circuit. In a circuit, it's always P=v(t)i(t) (or some variant).
It's not that the Veritasium video is wrong. It's the fact that Derek deliberately misleads you-without being technically wrong-that bugs me. I know he has to do click-baity stuff like that to grab eyeballs. Still, I find his _"everything you know is wrong"_ attitude quite irritating. Particularly because I coach high school students for competitive college entrance exams. I don't know what kind of schools Derek went to. But here in India, high school students do learn about transformers, electromagnetic waves etc. With equations (though not vector calculus just yet). We do tell them upfront that we're teaching them a simplified version of reality, and that they are free to study more complex models later on if they wish. We teach them stuff that they can build upon later, not stuff they have to forget and start over from scratch.
You teach them that the flow of charged particles is electricity, I = Q/t, P=VI etc., and they will reach the logical conclusion that in solid conductors, it's the electrons that carry the electrical energy. That mental model is sufficient for working with electrical circuits, so we don't correct it until a better model is required.
Some of my students watched the video in question, and sadly, got confused about the role of wires in an electrical circuit. They argued that since energy flows directly from the battery into the bulb through space, and not via electrons in the wire, all bulbs in the vicinity should light up, connected or not. At least, that's what the Poynting Vector diagram in the video implies.
No doubt, all the bulbs felt the EMP. (Though you can argue whether it caused any of the bulbs to "glow" in any meaningful sense.) However, any transient currents due to the EMP are very weak, and die down very quickly. After a short delay, the bulb that's connected to the battery starts glowing steadily-when electricity actually starts flowing through it. The length of the wire determines the delay. (There are transient currents through the wire as well, for that matter, but after a while, those too die down.) And the unconnected bulbs don't glow.
This isn't obvious from the video. The Poynting Vector diagram seems to imply that if you keep an unconnected bulb close to the connected one, both should glow steadily. Easy to disprove. Harder to explain Derek's motive.
Yes I think you are correct Kathy. Poynting Theory does not distinguish between potential and kinetic energy so flow that seems unphysical will probably be potential energy. With dc there will be energy flow inside the wire.
Worth noting that "the Jackson" is a well regarded textbook. That's one I've opened in my undergrad studies.
Jackson is THE bible in classical ED. If someone says Jackson is wrong on something, they better be prepared to bring proof.
Yes, it's a masterpiece: written by someone deeply passionate about the subject.
On his original video I asked what would happen if the wire had been in a circle of the same length instead of parallel lines connected at the far ends. No one answered
As long as the bulp would be at one meter of the battery and switch, the results would be the same.
If energy doesn’t flow on wires, why do they get hot?
the veritasium video was about not being "in" .
Well, you could argue that energy flows in the vacuum and the drift of electrons in the wire are just a consequence of the fields created by that energy flow. Wiring is just shaping that field, and the electron flow is a side effect.
I'll have to study all these video's to see how it stacks up to what I've been taught and also to adequately know what everyone is posing. Fortunately the subject at hand doesn't make any difference to current carrying capacity as we know it, but is interesting as I have been taught differing things throughout my life. 43 years ago 1980 at high school everything current, field, electron flow all went at the speed of light. As an Electrical technician doing a physics refresher course over a year in 2008 to keep the brain cells firing we were taught the electrical field is created at the speed of light but the electrons themselves move in a sporadic motion as they bounce and collide with atoms in the whole conductor and as such the actual distance travelled along the conductor is very low with out getting into differing variables, voltages etc. I'll have to watch the the original video in question but was confused when Cathy brought static electricity into the video. I love your video's Cathy they are a real treasure.
Congratulations on your book! Cheers...
Every circuit has both capacitance and inductance as well as resistance. There's an RC time constant and an RL time constant. It's easy to work out if you know the values of R L and C
Shots fired! You're amazing keep it up.
Thank you for the video, I unsubbed from Veritasium because Derrick lacks Veritas - he writes too much clickbait, which we already have way too much of.
I hate those "I'm an expert on everything channels" They're usually riddles with false information. I appreciate these kinds of videos
Your take on Feynman and his quote is totally incorrect. Feynman is not saying that you can't explain physics to dumb people, Feynman is saying that he wont dumb physics down for people. Einstein had a similar quote, something to the effect of "make things as simple as possible, but no simpler." You should consider the consequences of using a position of authority to convince people that they understand something when they actually don't.
I have your book, Kathy, and I admire it very much. You're doing good work.
what is the speed of electricity?
Overall, I found your video very good in that you present your argument with references without being attached to your view which we can comment on. But I think you're wrong in parts:
At the start of Derek's video, he says: "now you have to make certain simplifying assumptions about this circuit..." so listening between his words, I would still go with (d) 1/c; because to me, it looked simple enough to be modelled as a transmission line. Note he did a follow up video 'How Electricity Actually Works' confirming this, and showing the waveform of the pulses; where current clearly initially flows into the characteristic impedance of the transmission line, and lighting the bulb at a level lower compared to the DC steady state: but it still lights the bulb.
Voltage, energy density and the Poynting vector are physically meaningless locally, needing to be evaluated between two points, integrated inside a volume, integrated over a closed surface area respectively to give physically meaningful quantities. So the Poynting vector is mathematically consistent for DC circuits, so long as you don't try to create a physical picture on how it behaves locally, and stick with integrating it over a closed surface area to get the rate at which EM energy is crossing this closed surface. Also, the Poynting vector is part of the EM conservation of energy theorem derived from Maxwell's equations via the assumption that J.E = the rate at which work is done by currents and the electric field interacting with one another. It's also derived more elegantly from the Lagrangian for electromagnetism.