Prof. Lewin, You are arguing with people that agree with you but who have set up the problem differently. All electrical engineers know to include the inductance in the circuit measurement such that KVL holds. The only reason that you get the measurements you do in your lecture's experiment is because you didn't include the loop as a passive inductor component. If you would, it would account for the voltage created by the change in magnetic flux. Model it again as a transformer with two series resistors superimposed on the output and you find that KVL does work. People who build computers and generators use and understand Kirchhoff's laws and know how to apply them. You should be nicer to them!
Looks like you didn't learn anything from this video... When you're adding up the Voltages, if you include inductor voltage in your loop - you're by definition using Faraday's Law, not the Kirchoff Loop Rule. Also Earth is *not* flat.
@@SloeJuice Whose definition? You use KVL all the time when analyzing op-amps, and the loops in this case involve a major disconnect. KVL, as used in circuit analysis, allows for such assumptions and compensations.
Including the induced voltage as if it was a static voltage source like a battery is incorrect. The physics does not work that way. Including induced voltage is a *trick* that allows you to avoid thinking about it correctly. In reality you put those terms on the right hand side. The left hand side becomes the left hand side of KVL, and the right hand side becomes non-zero. This is not KVL, it is faraday's induction law for circuits. It's not about "setting up the problem differently", it is a matter of explaining the physics correctly.
Sir, I really wish you could watch Mr. Mehdi's video, and respond to him as you would any curious student. Science is held up by the burden of proof, and so people who disagree scientifically, in a legitimate manner should be given a chance at an explanation why there reasoning is wrong. We all love you as a great physics professor, but we hope that you can understand where Mr. Mehdi is coming from and explain scientifically. Thank you.
watch full video in the end of video prof say i will answer in next video you guys are electroboom fans and believe what electroboom tell you i'm not saying prof lewin is right but electroboom fans are saying electroboom is right
I am also mehdi's fan. But he didn't give a scientific mathematical explanation as dr.lewin did here. And what dr.lewin says makes perfect sence. Of course i am not saying mehdi didn't make any sence but he relies on the experimental results solely i want him to do a mathematical explanation of his experiment.
@@astafzciba What do you mean? He did give a scientific and mathematical explanation. Do you want him to sit in a huge laboratory to make it look more official? All he did was reconfirm a widely accepted theory in his way and was extremely respectful to Dr. Walter while he did that
I watched the video ElectroBOOM's major issues are related to KVL and Faraday's Law and to my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values *(as they should according to Faraday's Law).* It is clear from his video that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight. He has a masters degree in EE. His video is therefore an embarrassment.
@@Edward-ud8hd *I demonstrated at the end of my lecture #16 of my E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values. The reason is that in the case of an induced EMF (Faraday's Law) potentials are no longer determined and thus potential differences depend on the path. This is first year college Physics.* The same physics applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced (Faraday's Law). th-cam.com/video/b7i2uMx7gHo/w-d-xo.html My demo was suggested by Romer in 1982. I first did it in 1984 in my MIT course (8.02) and I have done it every time that I lectured 8.02. *Electroboom insulted me* *by mentioning in one of his videos that: "The entire reason Dr. Lewin was reading two different voltages was due to bad probing".* It would have been fine if this comment had been made by someone who has little background in Physics. But it's quite worrisome if it is made by someone who has a masters degree in EE. This demo has now become a classic; it's done all over the world at many colleges and universities. In addition, Kirchhoff's loop rule (KVL) is older than Faraday's Law. My translation of the *original work by Kirchhoff from 1845 which was after the publication of Faraday's Law* "(...) it becomes easy to find the requirement, which [voltage] you must fulfill, so that the electrical condition on the [metal] disk can be a stationary one. When we look at a closed loop in [the disk], inside of which no electricity is being fed into [the disk], then the sum of all amounts of electricity in this loop must be 0." The original text can be found at google books in the following link, book pages 497-514: books.google.de/books?id=Ig8t8yIz20UC. *Clearly Kirchhoff was fully aware of the prerequisite for his "loop rule", i.e. that d_phi(t)/dt must be equal to zero! If d_phi(t)/dt is not zero, then Faraday's Law has to be used.* *Faraday's Law always holds regardless of the value of dphi(t)/dt that's why it is one of Maxwell's eqs and Kirchhoff's Loop Rule (KVL) is not.*
@@Edward-ud8hd It's settled, EE Sadaghdar made a clarifying video backed up by Prof Belcher. It should be an academic dispute, but got AdHom unnecessarily. Prof Belcher also stated he found physics books to be "unclear" so most students came to wrong conclusions.
I absolutely LOVE this scientific rant developing live on TH-cam! Reminds me the good ol' days of science when Bernoulli blackmailed Newton over brachistochrones. Let's make Renaissance great again!
I think it is more a matter of playing with words and concepts rather than one interpretation being wrong and the other one being right. In circuit theory, an inductor is a component with "v=Ldi/dt" being the relation that relates its voltage to its current. And then it is believed that KVL (and also KCL) always work, which in fact is correct with these considerations. Now of-course if you ask one, how he has derived that relation for the voltage and current of inductor, he will answer through Faraday's law (as Dr. Lewin mentioned). In fact, from circuit theory point of view, you can see the inductor as a black box with its voltage and current relation being defined as "v=Ldi/dt" (In circuit theory you can even have black boxes with some customized relation between their voltage and current, for which there might not exist an equivalent component in real world).
Consider the counter argument before attacking it. Actually, watch the video that’s countering your argument before attacking it! That’s all I’m saying.
I watched the video ElectroBOOM's major issues are related to KVL and Faraday's Law and to my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values *(as they should according to Faraday's Law).* It is clear from his video that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight. He has a masters degree in EE. His video is therefore an embarrassment. To Agree or Not to Agree with the Master that is Not what Matters th-cam.com/video/ototTU5NUNA/w-d-xo.html
How dense do you have to be to create a video to dispute a counter-argument video you haven’t even watched yet? You and the person providing the counter-argument both fundamentally agree with Faraday’s Law, the only difference is that your circuit model was missing a component to keep it consistent with the secondary of a transformer. Quit bashing other respected people in the community (and their opinions on your teaching) while assaulting their high school education because you’re too great and glorious to look at a circuit a different way. I would get laughed out of my EE department and directed to the business college if I failed to model a system correctly. Respectfully, you’re drunk off your own kool-Aid.
I watched it *ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
Lectures by Walter Lewin. They will make you ♥ Physics. Guess it's true that more education only makes you less capable of of taking anyone serious. Sometimes even the intelligent need to be humble.
@@Mr3DPrintWizard says who? I guess you must be a professor in physics to challenge a legend like Walter Lewin like this. What you really say is that Mr. Lewin doesnt know what he speaks about.......
@@ModPapa That argument never existed. It's an unfinished trial to save validity of KVL in an arrangement where it is known to be invalid. He never calculated nor defined those 4 unknown voltages, and his "proper probing" is obviously wrong, I proved already. He didn't understand what Lewin said, therefore he must repeat his studies (and Dr. Lewin was so generous, that he gave Mehdi a free lession), or admit he is failed. Mehdi even used Lewin to gain profit and to destroy the credibility of Lewin and he also spreaded dezinformation. This is an insult for the subscribers also from Mehdi. This is how i see.
Its interesting how you like to argue and think up reasons for why people don't agree with you without actual going out and talking to people who have legit reasons for why they don't agree with you. There are tons of arguments against your video that you don't address and choose to ignore. Im gonna go on record that I didnt finish watching your video either. 😑😑
*ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
This shows a basic misunderstanding of everything Electroboom had to say. He replicated your results and then explained why your conclusion is wrong. Just deal with it.
What is taught in school is that sum of the voltages around a loop is zero at a given moment. This generalised rule includes induced voltage, because it doesn't specify how the voltage is formed. This is just arguing semantics. All those teachers mean faraday's law, but they only remember kirchhoff's name. It is not taught wrong, but only with a wrong name. No one is teaching that inductance doesn't have an effect.
>>>What is taught in school is that sum of the voltages around a loop is zero at a given moment. >>> *yes, I know, and that is DEAD WRONG if there is an induced emf*
@@lecturesbywalterlewin.they9259 overall answer to all these quetions lies in mathematics (irrotational theoram) that if curl of a quantity is not zero then any scaler quantity like voltage can not be defined... I dont understand why some people don't understand your love on true physics and without putting some efforts by themselves they start questioning you... I have seen your 8.02x lectures as an electronic student in INDIA salute to you sir... I will see 8.01x and 8.03x also very soon
I am starting my Assistant Prof position later this year and I hope and try my best not to fall in the trap of self-righteousness that you are suffering from, to need to insult someone who is merely asking you a question with utmost respect. Have the decency to at least watch his video before you demonize him like that!
*I appreciate the fact that this Physics may not be familiar to you. Don't feel embarrassed about it; you are not alone. However, it's never too late to get educated. The choice is yours. Maybe this will help you.* *I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html *Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.* *My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.* *Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.* *By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video (see @ footnote below) on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.* *Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT.* core.csu.edu.cn/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/C29636DB-AB80-49E0-BFAB-BCE00159F00E/0/lecsup41.pdf *(@) ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly I would have found that both voltmeters would have read the same value. He could not have been more wrong* *This is my only msg on this issue. This is too basic. "I teach physics, I do not argue with people who think they know but who don't" (quote from Neil deGrasse Tyson). I do not argue either with people who believe that the Earth is flat.* This video may also help some of you to digest why 2 Voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html *Below follows Problem 7.50 in Griffith. Notice the drawing which he copied from Romer and he wrote: "Notice that V1 is not the same as V2, even though they are connected to the same points! See R.H. Romer, Am, J, Phys.50, 1089 (1982)"* drive.google.com/file/d/1G1a8_YNvB8X9xddUD27x9PE-j7Xbfo3m/view
2009: The best thing happened to me was walter lewin lectures. I passed class 12 without physics and chemistry teacher (govt school and the teachers got transferred). I wasn't even aware JEE, AIEEE existed. I did bad in competitive exams. Suffered through bad education for 7 years to get a well paying job. Now the dust is settled after almost 10 years, what am I doing? Going through all his lecture along with lot of mathematics once again and getting all my education fixed. And it is a treat! I was convinced with faraday's law since 2009 (the demo blows me even today). Mr. Lewin, your lectures saved me. They taught me how to reason through slowly and to believe reason over gut.
I do not understand a single piece of this whole discussion, I'm just a regular software developer with no background in physics or math. But I do love physics and science in general and I do have a huge respect for both central figures here, Prof. Dr. Lewin and Mr. Sadaghdar. I just wanted to say that such discussion is beautiful. I can imagine things like this happening at the London Royal Society between respected and beloved science fathers of our past, and that's exactly how science is and should be made. Hundreds of scientists are following this discussion as it happens, each leaving their respective perceptions, I'm amazed. Thank you two for all respect and time put in place here. And thank you everyone who is trying to help them out.
*ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law and he also tries to imply that a modern version of KVL is identical to Faraday's Law. That is a joke, see my video 5 + 3 - 8 = 0. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
@@lecturesbywalterlewin.they9259 I watched his video. In no way it was harassment. He even pointed out multiple times that he is just a guy with a diploma on TH-cam and that you are a renovated professor and that he is most likely wrong. He presented his points very objectively and without saying a single bad word about you. Let alone discredit you. These words you have for him are very rude and disrespectful. If you disagree with him why don't you just objectively point out he is wrong? Instead inducing all this drama. You are a professor, sir, act professional.
@@ilmu011 I have pointed it out! *ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
Thank you Dr. Lewin for acting more collected and calm in your demonstration today as opposed to last week. It is far more professional and appropriate if trying to get your point across.
You are debating terminology and for some reason discriminating against induced voltages, for some reason saying that we shouldn't include induced voltages in using KVL. Let me ask you this. If you were designing a circuit that took mains AC voltage from your wall, would you include the voltage supplied by the mains (120V or 240V or whatever) in your sum for KVL? If so, why? By your argument, induced voltages shouldn't be counted. That voltage is only there because of a changing magnetic flux through the secondary winding of a distribution transformer. But maybe we don't have a transformer in the mix. Maybe you're running your house directly from a local generator. Well then that mains voltage is due to changing magnetic flux in the windings of the generator, so why are you counting that? Your determination to discriminate between electromagnetically induced voltages and other voltages is entirely arbitrary. Faraday's law tells us how to determine a voltage due to induction if we know the rate of change of magnetic flux, just like Ohm's law tells us how to determine a voltage across an ideal resistor if we know the current and resistance.
I watched the video ElectroBOOM's major issues are related to KVL and Faraday's Law and to my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values *(as they should according to Faraday's Law).* It is clear from his video that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight. He has a masters degree in EE. His video is therefore an embarrassment. watch this too: th-cam.com/video/ototTU5NUNA/w-d-xo.html
@@lecturesbywalterlewin.they9259 But professors introduce and teach this thing, this "new form of KVL" in universities. I am EE student too, and they taught me the same way. This is written in books. We say, the voltage of an inductor is L*di/dt. :/ By the way, thank you for your response, and keep doing physics!
@@susceptibility_ This "new form" is just a conversion of Faraday's law. It is like don't understand Faraday's Law and write it in a wrong way and say it is a "new form". IT IS NOT ACCEPTABLE!
Thank you mr. Lewin. Great video and the shirt is amazing too! Could you please actually watch Mehdi’s video and reply AFTER you watch it? This gesture will be greatly appreciated by A LOT of people (Mehdi has 2M subscribers). Mehdi is nowhere near you at theoretical physics, this is exactly why we all would love to hear the explanation from you about his experiment and what he made wrong in it. He in no way is doubting you, but rather wants to know whether he is wrong and if so, then what the mistake is. It is a bit embarrassing that in order to have a simple question addressed we have to chew through the chinese wall of teachers Ego first. YOU DID NOT EVEN WATCH HIS VIDEO. 🤦🏻♂️ Isn’t this an ignorance? This is not how science is done, this is how religion is done. By not watching his video you immediately leave science area and go into a religion area. I can see how a professor of your age can be embarrassed by this situation, but please tame your wild ego and give a legit analysis of his mistake, if you are so sure that there is one. We all will only appreciate that gesture and it will make you look much better in front of 2000000 people, not only 100-1000 students.
in other words: Kirchhoffs law (*1845) doesn't care about magnetic fields at all. Maxwell's equations (*1864) 19 years later do. To use Kirchhoff's Law to describe circuits with changing magnetic fields, you have to use "something" that is only described by Maxwell's equations. This "something" combined with Kirchhoffs law is **Faradays Law.** So from the Physical Position Dr. Lewin is absolutely right. I think the biggest problem is the communication between very practical and theoretical people. Often if someone is very deep into something, he/she has a hard time understanding the problems of people in other holes.
"he said I did bad probing, so like a 5yo I lashed out, tried to silence him by telling him to get educated" A manchild with a large ego. May be an intelligent individual in some aspects of reality, but he isn't really a "smart" individual in social terms. Can't even act like an adult when questioned.
I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values. th-cam.com/users/th-cam.com/video/nGQbA2jwkWI/w-d-xo.html This can also be demonstrated with a transformer. th-cam.com/video/b7i2uMx7gHo/w-d-xo.html The reason is that an induced EMF (Faraday's Law) creates a non-conservative E field. This means that moving a test charge between the same 2 points in a circuit can require a different amount of energy (even with opposite signs!). You still aren't getting any energy for free, because it comes from the source of the time-varying magnetic field. When a voltmeter reads a value V it means that the integral of E dot dL across the voltmeter is V. In cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value. Kirchhoff's original text can be found in the following link, pages 497-514: books.google.de/books?id=Ig8t8yIz20UC. Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not. My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics. This demo has now become a classic; it's done all over the world at many colleges and universities. *ElectroBOOM and Dirk Van Meirvenne believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true.* They each posted a video on their channel in which they claim to have proof for their wrong ideas. Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT. freepdfhosting.com/0813df09f5.pdf *ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly both voltmeters would have read the same value. He could not have been more wrong.* The following video may also help some of you to understand why 2 voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html I thank Mick Vall for his insightful comments.
thisis a mini lecture which address allthe key issues. I cannot improve on this. I therefore send it to all who have a misconception about Faraday's Law. I could alse have referred viewers to a page in then Feynman Lectures which would then be equivalent to what you call copy and pasting.
This obviously relates to your video where you have two voltmeters connected to the same two points, and the voltmeters show different results. I suspect that many people who have asked you questions, such as myself, are perfectly aware that KLR applies to steady state circuits. No argument. However, for the voltmeters to read differently, even though connected to the same two points, something about their position in space must be the cause. If we consider the voltmeters to be moving coil analogue devices, then the thing that makes the needles deflect is a flow of electrons. In this experiment, it will be a pulse of electrons. In the setup chosen, voltmeter V1 will get a different magnitude pulse, and in a different direction from the pulse in V2. If the connecting wires have no flux change through them and they have negligible resistance, then many of us struggle to see how this can happen. We can extend the wires many metres from the resistor and whatever is changing the flux, we can surround the resistor circuit in mu-metal, all sorts of variations. Surely the only thing that can give your result is a difference in a) where the wires are arranged and b) different flux changes in those wires. When I taught physics there was a standard problem of an aeroplane with metal wings and fuselage, flying through the Earth's magnetic field where the field was at an angle to the horizontal. This would induce an emf between the tips of the wings. The students had to calculate the emf. Simple. But then I would ask them, could they think of a practical way of measuring this emf to check their answer. Most would say yes, hook up a voltmeter in the fuselage with wires extending down the wings. I would then ask them to consider what effect there would be in the connecting wires as the wires passed through the magnetic field also. Great fun!
There are different readings when the Voltmeter wire is on either side of the loop because the wire is enclosing the flux from different sides and in each case the resistor in the path restricting the current flow and causing it to take the route into the voltmeter is a different value.
@@lecturesbywalterlewin.they9259 I don't want to disturb your lectures. But have you ever heard about Theo Jansens wind sculptures on beaches? They are Physics in action. I love the winds, because I'm from the North, but more I love you, Walter Lewin.
@@mimisunny1820 yes I know his work very well. I have seen a retrospective of his work in the US and I have seen some of his sculptures being blown by the wind
@@lecturesbywalterlewin.they9259 I hope, you enjoyed it, I nevr saw his work in reality. But because of Faradys Law I can post it here. It is a kind of art, I really adore. Because it is fragile et dynamic. And I hope you will have a very beautiful winter again. th-cam.com/video/LewVEF2B_pM/w-d-xo.html
If you are going to argue someones point, you first need to listen to and understand that point, or else your argument is completely invalid. You, sir, are invalid.
The book by Purcell at least agrees with you. At page 359 (3rd edition), "A consequence of Faraday's law of induction is that Kirchhoff's loop rule is no longer valid in situations where there is a changing magnetic field." At page 366, he treats the RL circuit by counting all the "ohmic components" on one side of the equation, and the "induced EMF" on the other side (which includes the inductor) of the equation. Then he points out that you can count the inductor as an element by itself by *defining* "voltage across the inductor" to treat it like the other elements.
"At least" ?!, I really falled in love with purcell book, and griffiths books about electrodynamics. I consider griffiths,jackson,purcell,landau the holy squadbible of electrodynamics. And I consider Purcell a great physicist because he can explain any really fancy hard thing in very intuitive way just like the great Mr. Feynmann.
@@lecturesbywalterlewin.they9259 Professor Lewin, I just decided to purchase Purcell's book and abandon Giancoli. Such a disgrace to make such horrifying mistakes that affect readers!
I think these equations below can help everyone to understand. e=-Nd¢/dt, e=-Ldi/dt So, i can say ¢=Li ¢=magnetic flux. i=instantaneous current. L=inductance of the path e=induced emf. N=number of coils. note N=1 because it's only a coil having single turn
You guys need to understand that when the magnetic flux changes, a NON-CONSERATIVE Electric field is also induced. That is why changing magnetic flux is able to induce currents, an electric field is present that does work on the charges and moves them. Kirchoff's Voltage Law for the Electric Potential at a point in a circuit is fundamentally based off of the Law of Conservation of Energy. It assumes that the energy that goes into moving the charges around a closed loop circuit is conserved. You can't have a circuit with conserved energy when outside effects (changing magnetic flux) are creating fluctuations in the current of the circuit. Thus, Kirchoff's Law only applies to the special case where everything is conserved and isolated. This is not representative of the real world because magnetic flux is constantly changing in almost all of our electronic related technologies. This is Professor Lewin's main assertion, from what I could gather.
I was taught of KVL as "the sum of voltage rise and drops across a loop is zero". I guess this is more apt definition. And the EMF induced can be incorporated as voltage rise or drops. Sir pease do talk on these forums. Really thanks a lot for making this video. But please do consider Mehdi Sadaghdar, he complains more about the wrong probing used. And allow me to disagree, but I really think the self inductance of the probing are missing from your equations (I might be completely wrong). Though Mehdi says that KVL always works, he doesn't say that Faraday's is wrong. And regarding sir not talking on the forums (comments section), sir please do discuss here. Mad people always keep saying different things. But the genuine and true curiosity, hunger for Physics should not go unsatisfied I feel. And all aspects of Science only advance and become more clear after disagreements, discussions and experimentation. So please do talk here in the comments section.
The sum of voltages form is what you get when you apply the integral form of KVL to a circuit diagram. Adding ad hoc corrective terms is good engineering, but it is essentially just admitting that the model was wrong to assume KVL.
Yes Professor Lewin is correct. For a d.c. transient current, during this short time when an inductance L component (solenoid) is present since it has inside a 3D field with dφ/dt monotonically changing Kirchhoff''s law is not holding. Kirchhoff''s law however is holding in an electric conductor circuit after the transient is passed and a stable D.C. current is flowing inside the circuit. Kirchhoff''s law is also holding for stable alternating a.c. current conductor circuits because the dφ/dt is not monotonic.
Saying someone has a religious belief in something just because they went through the trouble to experiment themselves and discovered that your experiment was flawed, is sad and pathetic. your thinking is dogmatic
It might be dogmatic, But at this point he actually showed why KLR does not always work. As you could clearly see, KLR holds if and only if, there is no changing magnetic field.
watch full video in the end of video prof say i will answer in next video you guys are electroboom fans and believe what electroboom tell you i'm not saying prof lewin is right but electroboom fans are saying electroboom is right
@@Theo0x89 this could become the Walter Lewin's Loop Rule It's going to be an infinite pain for us, at least until all of them will agree to just use faraday's law when it's needed
I think the problem happens because people define the problem differently. I think what KVL means is that in a closed wire that has reached equilibrium with a steady current, the energy gained by the charges flowing must be equal to the energy lost by it. This is a consequence of our assumption that the current is steady and the system is in equilibrium. Faraday's law just gives a measure of the energy gained by charges in a loop when there is a changing magnetic field. If there is no way for charges flowing in a loop to lose that energy (like a resistor or maybe in radiation), the charges would accelerate and the current would keep increasing and a steady state will not be reached. This does not happen in a typical wire where a steady state would be reached in a fraction of a second and the charges flowing in the wire would lose the equivalent amount of energy they gain and hence KVL would hold in general. I am an electrical engineer and I am not sure if what I say is always right but that I what I think. Remember the case when an ideal voltage source is connected to an ideal capacitor. At the instant, when the circuit is closed and there is no charge on the capacitor, KVL would not hold because the circuit has not reached steady state.
The point of argument of ElectroBoom and Professor Lewin is technical. Boom refers to points in a conductor circuit where the path of electric current is fixed and the same for both voltemeters whereas Professor Lewin refers to points in fields and fieldmeters without any current really induced between these points (fieldmeters are usually fluxgate or Hall sensor). A normal current induced voltemeter can not be used in the second case. Boom refers to potential measurement by measuring electric conductor circuit current and Professor Lewin to direct measurement of electrostatic emf in a field (air) without electric current produced. In the case of a field measurement even the slightest misalignment of the meters from a predefined in space location and position (a few degrees) will change the path and give a different reading due the charge interactions within the field. In a nutshell Kirchhoff's law applies for electric current conductors circuits and not for Electrostatic fields. But yes if the path is exactly the same meaning not only in lengh but also in 3D spatial orientation the measurements will be the same under the same conditions in a 3D field. Sometimes electric engineers and physicists are saying the same things but in a different language. :) Markoul Electrical Engineer p.s. the best experiment to see this effect is to use a dc magnetometer. The slightest movement will change the reading.
The only problem arises while not understanding the difference between conservative and non conservative electric fields while considering circuits having changing magnetic flux induced fields are non conservative they dont add up in KV loop coz potential energy for them cannot be defined, Hence I totally agree Faraday's Law is the fundamental law to go with and not KV loop law..👍
Great to hear you are going to go over your famous two voltmeters / two different readings experiment. I'd like to be able to do this experiment for myself, and working from memory here, I seemed to recall one or two technical details left me short of feeling I could do so. You may have just resolved that. I always wanted to check my understanding of that historic lecture by posing the question: 'to be clear, are you saying that the reading is voltmeter position on the bench dependent ?' - well to day you explicit told me YES. And that is great. I'm mathematically trained so when you discussed the non-intuitive aspects of path independence in conservative fields I was straight on board. But what didn't come across from the lecture, a difficulty because of working in 2d i think, is what the differing paths where ? Anyho. I hope this feedback contributes something and look forward eagerly to your next video.
There was actually a similar question in our physics exam, which asked us to state whether Kirchhoff's loop rule is valid in AC circuits. Although I got the answer right, it was really helpful to get a proper reason from you. Thank you so much, Professor. Wish I had come to know of your channel earlier than I did.
Dr. Lewin, Sir, I wanted to tell you that I bought your book and I love it. I've read it over and over so many times. Currently, I'm a missile engineer for US Navy. I have an EE and MS in Optical Engineering from UNC-Charlotte Institute. I watched all your lectures and applied many of the concepts in your 801, 802, and 803 to my work. Thank you, sir!!!
I've found the mistake in Freedman on chapter 30 which talks about inductance In my portuguese version of the third volume entitled "Electromagnetismo" , page 349 , after they derive the equations it says: "Assim justificamos o uso da equação 30.8 (the differential equation) na lei das malhas de Kirchhoff para a análise de circuitos" In fact they use multiple times Kirchhoff's loop rule throughout the chapter. I can't tell if they used it correctly or if they made the same mistake all over the chapter. (I'm worried because I always tought Freedman was a great base college physics) But now I know the book has it wrong. Thank you Dr.Lewin from Angola.
Sir thank you for your special effort you put in whenever you explain Physics (so much better than just a mediocre effort to explain them). But also please respect everyone have different abilities in understanding - please don't laugh at them.
Hello Peter. I was insulted by 2 viewers. They argued that 2 voltmeters attached to the same 2 points in a circuit always MUST show the same value. They broadcasted on their youtube channels that the reason I measured 2 different values was due to my incompetence "my bad probing". Here are the facts: *I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html *Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.* *My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.* *Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.* *By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.*
Thanks, Doctor. I have a lot more studying to do. I have always thought Kirchhoff’s laws hold, but that’s because I’ve only applied KVL and KCL in the special case. I work with “magnetics” in my job, but luckily for me it’s possible to design a good, efficient transformer without actually fully understanding Maxwell’s equations. The V, R, L , switch circuit you analyzed is exactly what I deal with on a daily basis in switching power supplies, except R is virtually negligible and the switch is a MOSFET. I’d feel a lot better if I had a better understanding of Maxwell’s equations. I think I’ll watch your lectures again, and this time, I’ll read the notes and work some experiments myself. Thanks again. My learning curve is steep, but hopefully I’ll get there.
While I agree with the comments that the way electrical engineers use KVL is usually correct I also agree with Lewin that their underlying reasoning if not wrong then at least is misleading in the sense of the correct understanding of the underlying physics. Moreover his demonstration showing that voltmeters attached to the same pair of points can measure different values proves how careful one has to be with the assumption that a circuit consists of only lumped elements that being the most basic assumption when one applies KVL and KIL. I also want to emphasize that all viewers should be grateful to Lewin for pointing out this problem, it cost them nothing to watch and learn from him. And instead of whining about the manners of an 82-year old man that are irrelevant to the question/problem, if they do not like his style they do not have to watch it, just skip the video; he owes them nothing.
Late to the party but Professor you are absolutely correct! It's a shame how many so-called "experts" don't even have a clear understanding of the basics and still feel qualified to act as an "educator". This is not politics or sociology, this is physics. Classical physics that has been backed up by numerous experiments and real-life applications and distilled by great minds such as Faraday and Maxwell. To agree or not to agree is not the question.
It is just a misunderstanding between "physicist " and "engineers". Physicists look at the circuit as a physical structure in the real world with elements are placed in it as being in the real world. In that case, the EMF is an extra source that is considered by Faraday law. But in the engineering world, we are working with a model of the physical system and the EMF induced in the circuit is modelled by an extra "inductor" element. The KVL is correct for the model and it does not hold for the actual physical circuit so if you correctly model the circuit the KVL is correct " in your model". The problem here is that Prof. Lewin is using the real representation of the physical circuit and thinks the KVL is not working there which makes sense because it is used in the wrong context. BTW this type of modelling and adding extra inductor is a simple tool that any engineer is using on a daily bases for modelling "electrical machines" and I believe it is due to different type of education and mindsets that physicists and engineers sometimes cannot understand each other.
I love your way of talking about physics and I highly respect your work. by the way there is some differences I have to mention: 1.the kirchoff voltage law isn't integral of electric field on a closed loop but it's the sum of the voltage differences around a closed loop. and these two are different. 2.according to the kelvins law we sum all of the voltage drops or gains in a closed circuit so we add that inductor voltage too. and of course if we want to analyse faradeys law we have to assume that the magnetic field is passing the whole circuit not the inductor. edit: to make it more simple kirchoff law is actually saying that any voltage produced in a loop would consume by something in thay loop so the energy conservation law does hold that way
Integral of E.dl = work done , which has units of energy. When Integral of E.dl = 0, that means work done along the closed loop = 0. What is the work done to move the current through each component of the circuit? By definition its voltage*charge. Sum (voltage*charge) = 0, since the same charge flows in the same circuit. Sum of voltage = 0 , which is KVL
@@iLoveTortex >>>Integral of E.dl = work done>>> *that is incorrect* VA - VB is the Integral of E.dl in going from A to B. *integral of E.dl is NOT energy*
The sum of voltage differences form is exactly what you get if you apply the integral equation to the circuit diagram. The two are not distinct things.
This is such a good explanation. Thank you very much Professor. Anyone who thinks that Kirchhof loop rule always works has to realize that such a thing means that Maxwell's 3rd equation (Faraday's law) is wrong. And such a thing is complete nonsense, and like you said, everything in physics and engineering would fall apart. Faraday says that "integral of E dot dl can be any value", but Kirchhof's loop rule says that "integral of E dot dl can only be 0". They can't both be true. So Kirchhof's loop rule is true IF AND ONLY IF "dphi / dt" is 0. That is like saying that "a + b = 0" is the same thing like "a + b = x, where x can be any number", meaning "a + b = 0 and a + b = 24 at the same time", which is complete nonsense.
people should understand that in science, we work with the experiment and conclude something. based on that conclusions we draw models that fits the conclusions. but going in the reverse direction is completely foolish.
One question still remains. Which one is the real Kirchhoff's law? Closed loop integral of E.dl = 0 (KVL according to Walter Lewin, which sometimes holds) Or Directed sum of voltages around a closed loop = 0 (KVL according to electrical engineers, which always holds) Clearly, the two are not equivalent, since one can measure the voltage across an inductor when the current is changing and it won't be zero, while E.dl will be 0.
Kirchhoff's loop rule (KVL) is older than Faraday's Law. To now introduce a "modern version" of KVL which is really Faraday's Law is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html
I wonder if electricity is somehow like physics and quantum physics. Or perhaps all other laws actually doesn't always work, we just haven't found the situation/condition where those laws we knew didnt apply?
Here's the answer: If inductance of wire is considered, which means "in the varying magnetic field, wires don't always have zero potential difference across it" is considered, then Kirchoff's law would be right. However, if you insist that in Kirchoff's law, the inductance of wires are not considered, then KVL does not apply. And that would be plainly a difference in definition of Kirchoff's law, and I personally don't think Kirchoff's law have the restriction that inductance of wires cannot be considered. If you intentionally "ignore the inductance of the wire and the induced voltage difference across the wire" and "claim that even under this practical case we shouldn't add a 'virtue inductor' in the circuit to symbolize the inductance of the wire", then you successfully defies your "simplified" version of KVL. Nevertheless, I would consider the "virtue inductor" an appropriate model to be implemented just as we treat "internal resistance" of cells as a "virtue resistor" in series with the original cells since it helps us better mimic reality in our circuit diagram.
All I know is the probing wire generates an opposite voltage to what you where trying to measure, just do to its positioning. Watch ElectroBOOM's video, Its not like you'll get electrocuted while watching it.
I watched it *ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
when an inductor is involved and current is changing, KVL doesn't work because of magnetic field energy storage in the inductor. It is as if voltage disappears, and it comes back as the current begins to decrease. KVL works fine when current is steady.
I think he is just frustrated that so many people insist on using it in cases where it is not applicable and still state it like it is a fundamental law of nature.
Sir, you are awesome! It's a great pleasure to be able to experience this time on Earth and learn from your lessons and your deep knowledge about Physics. Science works and people need to be educated. His classes have helped me both in the understanding and willingness to learn physics and in my personal development, today, I am a teacher, trained in physics and mechanical engineering because of you. I wish all the best for you and continue with your work until the last day, you are a special person. Obs: I bought your book and it will be coming to my house soon. Super eager to read it. :)
Thanks Prof Lewin. One of the big problems in teach physics is teaching the wrong concepts, rule vs law, KLR is a rule not a law and Faraday is a law of nature.
So basically this whole problem/feud that raised a lot of unpolite responses and even racist remarks, just because a different definition of one Kirchoff Law, is it the loop rule or voltage law, I don't know. But weirdly both of the guys agree, that if you have the inductance of the loop considered the sum of voltages would equal zero, just that one calls it the faraday law and the other calls it MKVL... Was this a real thing? People did call themselves frauds and went full racists because the name of the rule, even though both agree that change in magnetic field will produce an emf? I do admit that I was impressed with the experiment results, and was a really cool, but not cool enough to justify racism and all other types of name calling...
Hi DR. Lewin - I have an easy experiment that show that KVL does not always work; and other experiment that show that Faraday’s Law also sometime doesn't work , but using KVL law we can solve problems even in the case that Faraday’s Law does not work. Sound a bit fantastic but can easily explained (1 Trasmition line (KVL can't explain it ) 2) Bi-Polar transistor (Fraday's law can't explain it) 3) Bi-Polar Transistor lumped model in the conduction region can be solved w KVL. - I can provide full answer in email . As EE eng I agree that KVL is special case of Faraday’s Law BUT I do not agree that KVL is useless. on the contrary for engineers KVL is much more practical for use and solve complex problem relatively easily than to use Faraday’s Law. It is not a matter of belief - engineers "make" KVL to "always work" by a change to the problem
*I appreciate the fact that this Physics may not be familiar to you. Don't feel embarrassed about it; you are not alone. However, it's never too late to get educated. The choice is yours. Maybe this will help you.* *I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html *Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.* *My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.* *Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.* *By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video (see @ footnote below) on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.* *Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT.* core.csu.edu.cn/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/C29636DB-AB80-49E0-BFAB-BCE00159F00E/0/lecsup41.pdf *(@) ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly I would have found that both voltmeters would have read the same value. He could not have been more wrong* *This is my only msg on this issue. This is too basic. "I teach physics, I do not argue with people who think they know but who don't" (quote from Neil deGrasse Tyson). I do not argue either with people who believe that the Earth is flat.* This video may also help some of you to digest why 2 Voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html *Below follows Problem 7.50 in Griffith. Notice the drawing which he copied from Romer and he wrote: "Notice that V1 is not the same as V2, even though they are connected to the same points! See R.H. Romer, Am, J, Phys.50, 1089 (1982)"* drive.google.com/file/d/1G1a8_YNvB8X9xddUD27x9PE-j7Xbfo3m/view
You have failed to address the raised issues again. The main one is your faulty measurement methods which leads you to believe that 2 voltmeters connected to the same point can read different values. If your setup induces a current on the voltmeter leads and you get different results depending on where the leads are positioned, that means your measurement setup is invalid. Because in such a case you will not be measuring the voltage accross point A and B. The voltage accross A and B will be the same with any number of voltmeters if you know how to probe right. You are ABSOLUTELY WRONG to state that the voltage is undetermined. Please think about this point and explain it clearly.
>>>> The main one is your faulty measurement methods which leads you to believe that 2 voltmeters connected to the same point can read different values.>>>> *Get educated.* Watch my 8.02 lecture #16 and the video which I will post today or tomorrow and look at the article written in 1982. www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf
Think clearly when you say "voltage between A and B". When there is a changing magnetic field, the voltage measures depends on the path of the probe right? So a unless you create a convention on the path measure the voltage, it is indeed undefined. This is especially true when there are people working with plasma that simply cannot use the circuit model! Of course engineers who deal with circuit everyday will set up a convention to probe the voltage along the circuit but that is by no means should be treated as definition of voltage.
@@wmh829386 I guess we disagree about the definition of Voltage there. What if we measure the voltage with shielded cables? If the probes are affected by the field, the measurement is simply invalid. Furthermore, it is possible to calibrate the probe to remove its effect from the measurement. Dr. Lewin may be a good educator and physicist but he is wrong here. The conclusion that the voltage is undefined is wrong. We can put this circuit in a EM simulator and calculate the voltage at any point and time.
KVL does work iff you take the closed loop integral of the ELECTROSTATIC FORCE, the conservative force , excluding any contribution of the induced electric field.
*I appreciate the fact that this Physics may not be familiar to you. Don't feel embarrassed about it; you are not alone. However, it's never too late to get educated. The choice is yours. Maybe this will help you.* *I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html *Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.* *My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.* *Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.* *By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video (see @ footnote below) on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.* *Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT.* core.csu.edu.cn/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/C29636DB-AB80-49E0-BFAB-BCE00159F00E/0/lecsup41.pdf *(@) ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly I would have found that both voltmeters would have read the same value. He could not have been more wrong* *This is my only msg on this issue. This is too basic. "I teach physics, I do not argue with people who think they know but who don't" (quote from Neil deGrasse Tyson). I do not argue either with people who believe that the Earth is flat.* This video may also help some of you to digest why 2 Voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html *Below follows Problem 7.50 in Griffith. Notice the drawing which he copied from Romer and he wrote: "Notice that V1 is not the same as V2, even though they are connected to the same points! See R.H. Romer, Am, J, Phys.50, 1089 (1982)"* drive.google.com/file/d/1G1a8_YNvB8X9xddUD27x9PE-j7Xbfo3m/view
🔰 Can anyone answer my questions... A) Is Dr. Levin saying that the ‘DC’ current passing through the inductor, (in an instant) is producing a changing magnetic field OR (I think I’m asking the same thing) B) Is he saying that from the time the DC current initially starts to flow until the peak voltage occurs, that in this nanonano second, that there’s a changing magnetic field, and therefore there is an initial voltage present it’s just that we can’t see it❓ C) Is Dr. Levin saying that the voltmeter is reading a voltage across the inductor (coil) and we just can’t see it, because of the voltmeter’s circuit❓ D) Is he strictly speaking to DC current❓ flow of inductor current is constant and not changing such as in a steady state DC current, then the induced emf voltage will be zero because the instantaneous rate of current change is zero, di/dt = 0. ✔️ This is from a well known website... Is Dr. Levin saying this is wrong ? “With a steady state DC current flowing through the inductor and therefore zero induced voltage across it, the inductor acts as a short circuit equal to a piece of wire, or at the very least a very low value resistance. In other words, the opposition to the flow of current offered by an inductor is very different between AC and DC circuits.” www.electronics-tutorials.ws/inductor/inductor.html Forgive my lack of understanding...
My friend and me, he studied electronics, were doubting the last video, understanding electrobooms explanation. But this one is completely clear. in fact i had never head of KLR in integral form.
Well ... what does an inductor " fighting a changing current" even mean in electrical terms ? Imho at t=0 there is no current because the voltage over the inductor is minus the battery voltage, leaving 0 V over the resistor. KLR intact. That's how the inductor "fights" the current. I don' t understand where this idea from the professor that there can be no voltage over a perfect inductor originates. It makes no sense. Imho the professor has a religious belief that there can be no voltage over a perfect inductor. ( I hope you do not consider this rude professor. Your have a 99 % credit of correctness in all other cases which is kind of neat ). Anyway, I'm not religious and certainly not in this case. If the professor actually is right I do hope he convinces me as soon as possible and it will be the happiest day of my life. Really. What in the case the current has reached the maximum or lets say 99 % and the switch is opened. In my experience a huge voltage spike will follow. Infinite in theory but limited by various non perfect factors. For example sparks will form between inductor terminals. But I guess the sparks will form a loop where KLR will check out according to the professor' s explanation. But why do they start in the first place ? It's interesting to realise that the professor cannot be proven wrong by experiment. If measuring over the inductor with a voltmeter proves nothing because it forms it's own loop then there cannot be proof of voltage over the inductor. Like Schrodingers cat. If we do not measure the voltage ( or open the box ) does it mean anything to say there's a voltage ( or a living cat ) ? I guess not ..... Maybe there's a clue there :-).
A perfect inductor is made out of nothing but superconducting wire. In a superconductor, no energy is dissipated and so no electric field can exist inside a superconductor. A changing magnetic field doesn't induce an electric field into the inductor, it adds curl to the total electric field, so it is no longer a conservative field. The notion of voltage over the inductor becomes path-dependent and therefore is ill-defined.
_"what does an inductor " fighting a changing current" even mean in electrical terms ?"_ Lenz's law says that the changing magnetic field induces an electric field that "fights" the change of current. _"I don' t understand where this idea from the professor that there can be no voltage over a perfect inductor originates."_ As you can see in the video, there is a voltage over the inductor in the sense that a voltmeter measures a voltage. But the line integral over the electric field along the windings of the inductor is zero. That's all there is to it. Walter Lewin believes that Kirchhoff's law is about the line integral, while people who actually analyze circuits in real world application use the real Kirchhoff's law, which is about the measured voltages over circuit elements like the inductor. _"sparks will form between inductor terminals [...] why do they start in the first place ?"_ Again, Lenz's law says that the changing magnetic field induces an electric field that "tries" to maintain the current, creating a huge voltage. _"If measuring over the inductor with a voltmeter proves nothing because it forms it's own loop"_ Well that's the big question here. If it is possible to arrange the probe wires so that all induced voltages in the wires cancel, then you can test Kirchhoff's law experimentally (the real one, not Lewin's).
"Imho at t=0 there is no current because the voltage over the inductor is minus the battery voltage, leaving 0 V" - agree with that, and that determines the slope of the rise in current. The rise in current will such as to create a voltage across inductor equal to that of battery. In the next moment, when there is some current, the rise in current will be smaller, as some voltage will be reduced in the resistor, and inductor will need lesser voltage over it to hold KVL. Following this logic moment by moment, you get the LR curve shown in the picture, and at each instant you use KVL. (I don't know if KVL hold in general, that's WAY beyond me, but for an LR circuit with DC or AC, from every EE textbook and computer simulations, it holds for sure.)
But that is wrong. The voltage over the inductor is not the negative of the battery. Were you not listening when the professor said it is a superconducting inductor? You are basing your answer on nothing, while the professor is basing his answer on the physics of superconducting wires. Who is the religious fanatic here? You or the professor? Also, this video clearly shows in the first minutes why Kirchhof's loop rule DOES NOT WORK. Both Kirchhof and Faraday can't be right at the same time, because one says that integral of E dot dl is always zero, and the other says that it's not true, and it can take any value. Faraday's law is part of Maxwell's equations, and if you are not insane, you know Maxwell's equations are true, hence Faraday is true, hence Kirchhof is false. End of discussion. If a + b = 0 and a + b = 12 (or any other number) only one can be true. I hope that is obvious. If the first is equivalent to Kirchhof and the second to Faraday, and if you believe Maxwell's equations, the first one is the false one. If you disagree, you are disagreeing with every physicist ever, not just the professor. Maxwell's equations are solid.
@@photonenbremse: Absolutely no energy is dissipated in a perfect inductor. But there is voltage as long as there's increasing current. The case is that the energy fed into that inductor is converted into a magnetic flux. Not dissipated. When the switch is opened the magnetic flux will decrease and the energy will come out in the form of a high voltage spike with a high impedant load when sparks may form. If its terminals are connected with a resistor the energy will be dissipated in the resistor. If it's shorted with another superconductor no energy is dissipated and the magnetic field will persist as does happen in the superconducting inductor in an mri machine..
*I appreciate the fact that this Physics may not be familiar to you. Don't feel embarrassed about it; you are not alone. However, it's never too late to get educated. The choice is yours. Maybe this will help you.* *I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html *Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.* *My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.* *Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.* *By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video (see @ footnote below) on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.* *Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT.* core.csu.edu.cn/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/C29636DB-AB80-49E0-BFAB-BCE00159F00E/0/lecsup41.pdf *(@) ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly I would have found that both voltmeters would have read the same value. He could not have been more wrong* *This is my only msg on this issue. This is too basic. "I teach physics, I do not argue with people who think they know but who don't" (quote from Neil deGrasse Tyson). I do not argue either with people who believe that the Earth is flat.* This video may also help some of you to digest why 2 Voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html *Below follows Problem 7.50 in Griffith. Notice the drawing which he copied from Romer and he wrote: "Notice that V1 is not the same as V2, even though they are connected to the same points! See R.H. Romer, Am, J, Phys.50, 1089 (1982)"* drive.google.com/file/d/1G1a8_YNvB8X9xddUD27x9PE-j7Xbfo3m/view
Off topic but dose anybody get the vibe that this older gentle man did ALOT of lsd back in the day 😂, not insulting his intelligence in anyway as he is sharp as a tack and easly out knowledge me any day. But he definitely has a "trippa" vibe about him
(9:11) In my opinion, people who 'religiously' believe in kirchoff's loop law, considers d(phi)/dt as potential (back emf) across the inductor hence include it in the closed loop integral for the circuit(which is of course incorrect) and so according to them kirchoff's loop law always holds. Thank you.
The problem is not that Kirchhoff's law is wrong. The problem is that you cannot remove a circuit from its environment. So assuming that the circuit is in a void, both of energy and matter, then it would hold true. So please don't say that it is not true, only say that it cannot be applied to every situation because of parasitic influences with the environment.
I never said that Kirchhoff's Loop rule is wrong. It's a special case of Faraday's Law. FL always works KVL only works if dphi/dt in FL is zero Kirchhoff's loop rule (KVL) is older than Faraday's Law. To now introduce a "modern version" of KVL which is really Faraday's Law is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html
I don't know how this could be made any more clear. I think what people don't understand in the induced EMF volt meter demonstration is that the meter and the wire leading to it is part of the coil. It's not really measuring between the two points it is connected to, it measures the part of the coil it is located at. By the way, I don't remember ever hearing of Kirchoff's loop rule before your video about it. Probably this was taught in school, but I don't remember hearing the name. I do remember hearing about Faraday's law.
Agree with you but there is a much more simple explanation why Kirchoff law does not apply. If you energize a circle of copper wire the energy disappear, but if you energize a capacitor, wich is practically the same, the energy stays
When given the option to analyze a circuit in terms of voltage or current, is current the more 'natural' choice then? It seems like current-based analysis holds in more situations than voltage-based analysis. Current must be conserved in a loop because of conservation of mass/charge (ie the 'stuff' in the loop) but ultimately voltage isn't? Is it because of voltage cannot be analyzed at a single point but current can?
Im only a junior in EE and love Walter Lewin, I watch all his videos even if at some points they are over my head. My only gripe is I know Mr. Lewin really does not care to debate the topic but I would respectfully love it if he would on a personal basis talk with Mehdi from ElectroBOOM and show him where he is wrong. There is a productive reason behind this and that is if Mr. Lewin can show Mehdi where he is wrong (Mehdi will gladly accept he is wrong if he is) then Mhedi's new found understanding will translate to 1.9million others who may potentially ask the same question one day. Pass the information on a personal basis to those that can help pass it to the masses. I will always love your lectures but please understand that some people may learn more from a different platform style.
I do not debate whether the Earth is flat or not and I do not discuss whether Faraday's Law is correct or not. FL is classic 1st year college Physics and it is very basic. Viewers have access to all my lectures. *ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
One last thing and I will bow out. Please try to remember in this chaotic world of polotics, wars, lies and human suffering all of us here watching your lectures and those of us who watch his entertaining videos are here to learn. In school systems defined by govenment and financial systems some of us must undertake inadaquate teachings from lack luster professors and in todays world we rely heavily on outside sources. I have used your videos to understand "concrete" learnings that were skimmed over in my community college and people like Mehdi from ElectroBOOM serves to keep me entertained in a smart way when crunching the numbers gets overwhelming. This day and time youtube teaches us more than a class room and if those of you that have the followers play nice and work together you call affect millions of people in a positive way. Nothing but respect from a 38 year old low level student.
the current conservation (1 of K's Laws) always applies. But that was not the issue here. None of K's laws are one of Maxwell's 4 eqs because you do not need them.
Dr. Lewin, this question is actually not arguing your explanation at all but maybe to better understand something "basic". Why do we say electricity moves from positive to negative "conventional theory"? Does it actually move from negative to positive "electron flow theory"? If you explain this in a lecture, could you please send me a link or refer me to that lecture? Thank you! Your work is amazing and your explanations are fantastic
Thank god we a teacher like you ms lewin , the other source want to teach us a wrong laws , the video is clear and absolutly we understund now (alhamdulilah) that kirshoff law doesnt work in all case . So clear why people doesn't understund
Good video. 22:08 - There are actually 3 (not 2) reasons why people have a religious belief in Kirchhoff. And, the 3rd reason (goes to the heart of this debate, and) is because by applying Kirchhoff where it may not be suitable and in (questionable) ways that model the EMF as a voltage drop they can still get the correct answers. This is like a dog chasing the wrong cat up the correct tree. Essentially, people can “re-jig” the approach and/or circuit so that KVL (roughly) applies (for circumstances where delta EMF doesn’t = 0) and - even though that approach is fundamentally incorrect in terms of Faraday and Maxwell - they still arrive at the correct answer. But in doing so (whilst it seems that approach validates the application of KVL in circumstances where delta EMF doesn’t = 0) they actually arrive at the correct answer in a manner that conceals how the path they took to get there was not entirely consistent with Faradays Law; and therefore questionable. See my comments here for more detail. th-cam.com/video/nGQbA2jwkWI/w-d-xo.html Particularly point “I”. Bottom line number 1; is that so long as you know you’re applying KVL in a manner that is fundamentally incorrect to such an extent that you're also aware of the limitations/constraints of that approach, even if you do arrive at the correct answer, then I guess it’s your choice. However, the problem with that approach (aside from the fact that it is fundamentally misaligned with Faradays Law; which should be a cluster of red flags for anyone pursuing accuracy/precision) is that it can develop a false sense of security in what you analyse, test, and also claim; which could lead to bigger mistakes. Bottom line number 2; is if your approach is derived from Faradays Law (as KVL is) but is not entirely consistent with Faradays Law, then Faradays Law applies. Meaningfully considering this removes the issues associated with the fact that both parties (Electroboom and Professor Lewin) probably probed their circuits in ways that supported their intentions/results; although that in itself is not necessarily the main issue.
I am a student of standard 12th and our class ran into the same discussion, my teacher explain all the students in the same way as Dr.Lewin did. It was not at all hard to understand, I dont know why these *big brain* people in comments are getting mad about...
May I ask you where can I post solutions to your problems?As I already sent solution of problem 47 in one of your fb accounts ... but not sure whether its yours!
![ปฏิเสธไม่ไหว (Crush on you) - LIPTA feat. No One Else [Official MV]](http://i.ytimg.com/vi/NBw1jF342vw/mqdefault.jpg)
Prof. Lewin,
You are arguing with people that agree with you but who have set up the problem differently. All electrical engineers know to include the inductance in the circuit measurement such that KVL holds. The only reason that you get the measurements you do in your lecture's experiment is because you didn't include the loop as a passive inductor component. If you would, it would account for the voltage created by the change in magnetic flux. Model it again as a transformer with two series resistors superimposed on the output and you find that KVL does work.
People who build computers and generators use and understand Kirchhoff's laws and know how to apply them. You should be nicer to them!
This is so true, the prof is just trying to make a point that is so obvious that people are confused because they used to compensating for it.
Looks like you didn't learn anything from this video... When you're adding up the Voltages, if you include inductor voltage in your loop - you're by definition using Faraday's Law, not the Kirchoff Loop Rule. Also Earth is *not* flat.
@@SloeJuice Whose definition? You use KVL all the time when analyzing op-amps, and the loops in this case involve a major disconnect. KVL, as used in circuit analysis, allows for such assumptions and compensations.
Including the induced voltage as if it was a static voltage source like a battery is incorrect. The physics does not work that way. Including induced voltage is a *trick* that allows you to avoid thinking about it correctly. In reality you put those terms on the right hand side. The left hand side becomes the left hand side of KVL, and the right hand side becomes non-zero. This is not KVL, it is faraday's induction law for circuits. It's not about "setting up the problem differently", it is a matter of explaining the physics correctly.
@@SloeJuice Gee, kinda a kick in the nuts by you! Really?
Sir, I really wish you could watch Mr. Mehdi's video, and respond to him as you would any curious student. Science is held up by the burden of proof, and so people who disagree scientifically, in a legitimate manner should be given a chance at an explanation why there reasoning is wrong. We all love you as a great physics professor, but we hope that you can understand where Mr. Mehdi is coming from and explain scientifically. Thank you.
watch full video in the end of video prof say i will answer in next video you guys are electroboom fans and believe what electroboom tell you
i'm not saying prof lewin is right but electroboom fans are saying electroboom is right
Earth is flat.
I am also mehdi's fan. But he didn't give a scientific mathematical explanation as dr.lewin did here. And what dr.lewin says makes perfect sence. Of course i am not saying mehdi didn't make any sence but he relies on the experimental results solely i want him to do a mathematical explanation of his experiment.
@@astafzciba What do you mean? He did give a scientific and mathematical explanation. Do you want him to sit in a huge laboratory to make it look more official?
All he did was reconfirm a widely accepted theory in his way and was extremely respectful to Dr. Walter while he did that
@@astafzciba I think mehdi's probing method interferes with the flux of the circuit and gives a bad result.
Truly a shame you can’t even be bothered to watch his video and check the scientific consensus.
I watched the video
ElectroBOOM's major issues are related to KVL and Faraday's Law and to my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values *(as they should according to Faraday's Law).* It is clear from his video that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight. He has a masters degree in EE. His video is therefore an embarrassment.
@@lecturesbywalterlewin.they9259 Dr. Lewin knows what he's doing and his lectures are already there to help. Why so much hate?
@@lecturesbywalterlewin.they9259
He has a masters degree in EE. his video is therefore an embarrassment? So childish.
@@Edward-ud8hd *I demonstrated at the end of my lecture #16 of my E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values. The reason is that in the case of an induced EMF (Faraday's Law) potentials are no longer determined and thus potential differences depend on the path. This is first year college Physics.* The same physics applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced (Faraday's Law). th-cam.com/video/b7i2uMx7gHo/w-d-xo.html
My demo was suggested by Romer in 1982. I first did it in 1984 in my MIT course (8.02) and I have done it every time that I lectured 8.02. *Electroboom insulted me* *by mentioning in one of his videos that: "The entire reason Dr. Lewin was reading two different voltages was due to bad probing".* It would have been fine if this comment had been made by someone who has little background in Physics. But it's quite worrisome if it is made by someone who has a masters degree in EE. This demo has now become a classic; it's done all over the world at many colleges and universities.
In addition, Kirchhoff's loop rule (KVL) is older than Faraday's Law. My translation of the *original work by Kirchhoff from 1845 which was after the publication of Faraday's Law* "(...) it becomes easy to find the requirement, which [voltage] you must fulfill, so that the electrical condition on the [metal] disk can be a stationary one. When we look at a closed loop in [the disk], inside of which no electricity is being fed into [the disk], then the sum of all amounts of electricity in this loop must be 0." The original text can be found at google books in the following link, book pages 497-514: books.google.de/books?id=Ig8t8yIz20UC. *Clearly Kirchhoff was fully aware of the prerequisite for his "loop rule", i.e. that d_phi(t)/dt must be equal to zero! If d_phi(t)/dt is not zero, then Faraday's Law has to be used.* *Faraday's Law always holds regardless of the value of dphi(t)/dt that's why it is one of Maxwell's eqs and Kirchhoff's Loop Rule (KVL) is not.*
@@Edward-ud8hd It's settled, EE Sadaghdar made a clarifying video backed up by Prof Belcher.
It should be an academic dispute, but got AdHom unnecessarily.
Prof Belcher also stated he found physics books to be "unclear" so most students came to wrong conclusions.
I absolutely LOVE this scientific rant developing live on TH-cam!
Reminds me the good ol' days of science when Bernoulli blackmailed Newton over brachistochrones.
Let's make Renaissance great again!
how old are you
@@ashkara8652 19
Best comment ever!
I think it is more a matter of playing with words and concepts rather than one interpretation being wrong and the other one being right.
In circuit theory, an inductor is a component with "v=Ldi/dt" being the relation that relates its voltage to its current. And then it is believed that KVL (and also KCL) always work, which in fact is correct with these considerations. Now of-course if you ask one, how he has derived that relation for the voltage and current of inductor, he will answer through Faraday's law (as Dr. Lewin mentioned).
In fact, from circuit theory point of view, you can see the inductor as a black box with its voltage and current relation being defined as "v=Ldi/dt" (In circuit theory you can even have black boxes with some customized relation between their voltage and current, for which there might not exist an equivalent component in real world).
Consider the counter argument before attacking it. Actually, watch the video that’s countering your argument before attacking it! That’s all I’m saying.
I watched the video
ElectroBOOM's major issues are related to KVL and Faraday's Law and to my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values *(as they should according to Faraday's Law).* It is clear from his video that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight. He has a masters degree in EE. His video is therefore an embarrassment.
To Agree or Not to Agree with the Master that is Not what Matters
th-cam.com/video/ototTU5NUNA/w-d-xo.html
i think the professor never sow the arguments of the other side.
He did.
How dense do you have to be to create a video to dispute a counter-argument video you haven’t even watched yet? You and the person providing the counter-argument both fundamentally agree with Faraday’s Law, the only difference is that your circuit model was missing a component to keep it consistent with the secondary of a transformer. Quit bashing other respected people in the community (and their opinions on your teaching) while assaulting their high school education because you’re too great and glorious to look at a circuit a different way. I would get laughed out of my EE department and directed to the business college if I failed to model a system correctly. Respectfully, you’re drunk off your own kool-Aid.
I watched it
*ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
Lectures by Walter Lewin. They will make you ♥ Physics. Guess it's true that more education only makes you less capable of of taking anyone serious. Sometimes even the intelligent need to be humble.
@@Mr3DPrintWizard says who? I guess you must be a professor in physics to challenge a legend like Walter Lewin like this. What you really say is that Mr. Lewin doesnt know what he speaks about.......
@@aslerunarborgersen5175 "Legend".
A legend doesn't take an argument as an insult.
@@ModPapa That argument never existed. It's an unfinished trial to save validity of KVL in an arrangement where it is known to be invalid. He never calculated nor defined those 4 unknown voltages, and his "proper probing" is obviously wrong, I proved already. He didn't understand what Lewin said, therefore he must repeat his studies (and Dr. Lewin was so generous, that he gave Mehdi a free lession), or admit he is failed. Mehdi even used Lewin to gain profit and to destroy the credibility of Lewin and he also spreaded dezinformation. This is an insult for the subscribers also from Mehdi. This is how i see.
Its interesting how you like to argue and think up reasons for why people don't agree with you without actual going out and talking to people who have legit reasons for why they don't agree with you. There are tons of arguments against your video that you don't address and choose to ignore. Im gonna go on record that I didnt finish watching your video either. 😑😑
*ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
I would love to see Prof. Walter demonstrating the Electrobooms experiment with analysis and clearing the air out..
Watch my 8.02 lecture #16
Most people here didn't watch Dr. Lewin's lectures.
Was this debate ever settled? Sorry I'm out of the loop.
@@Ghostrider-ul7xn there's no settlement possible between a physicist and an engineer, their perspectives are too different
This shows a basic misunderstanding of everything Electroboom had to say. He replicated your results and then explained why your conclusion is wrong. Just deal with it.
EB's conclusion violated Faraday's Law. It's simple as that. Dr. Lewin had to explain the whole thing over again!
@@nahiyanalamgir7614 no
Thanks for everything professor. You've done a lot of good for a lot of people through your teaching.
:)
What is taught in school is that sum of the voltages around a loop is zero at a given moment. This generalised rule includes induced voltage, because it doesn't specify how the voltage is formed. This is just arguing semantics. All those teachers mean faraday's law, but they only remember kirchhoff's name. It is not taught wrong, but only with a wrong name. No one is teaching that inductance doesn't have an effect.
>>>What is taught in school is that sum of the voltages around a loop is zero at a given moment. >>>
*yes, I know, and that is DEAD WRONG if there is an induced emf*
@@lecturesbywalterlewin.they9259 overall answer to all these quetions lies in mathematics (irrotational theoram) that if curl of a quantity is not zero then any scaler quantity like voltage can not be defined...
I dont understand why some people don't understand your love on true physics
and without putting some efforts by themselves they start questioning you...
I have seen your 8.02x lectures as an electronic student in INDIA
salute to you sir... I will see 8.01x and 8.03x also very soon
@@lecturesbywalterlewin.they9259
Induced EMF isn't voltage?
@@samial-terkawihasib335 Induced EMF arises from a changing magnetic field. Faraday's law is based on that.
I am starting my Assistant Prof position later this year and I hope and try my best not to fall in the trap of self-righteousness that you are suffering from, to need to insult someone who is merely asking you a question with utmost respect. Have the decency to at least watch his video before you demonize him like that!
*I appreciate the fact that this Physics may not be familiar to you. Don't feel embarrassed about it; you are not alone. However, it's never too late to get educated. The choice is yours. Maybe this will help you.*
*I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html
*Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.*
*My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.*
*Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.*
*By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video (see @ footnote below) on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.*
*Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT.* core.csu.edu.cn/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/C29636DB-AB80-49E0-BFAB-BCE00159F00E/0/lecsup41.pdf
*(@) ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly I would have found that both voltmeters would have read the same value. He could not have been more wrong*
*This is my only msg on this issue. This is too basic. "I teach physics, I do not argue with people who think they know but who don't" (quote from Neil deGrasse Tyson). I do not argue either with people who believe that the Earth is flat.*
This video may also help some of you to digest why 2 Voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html
*Below follows Problem 7.50 in Griffith. Notice the drawing which he copied from Romer and he wrote: "Notice that V1 is not the same as V2, even though they are connected to the same points! See R.H. Romer, Am, J, Phys.50, 1089 (1982)"* drive.google.com/file/d/1G1a8_YNvB8X9xddUD27x9PE-j7Xbfo3m/view
@@lecturesbywalterlewin.they9259 Are you STILL copy/pasting that same garbage?
@@MrIkesimba haha, are you upset simba? The cartoonish lionking is roaring.
2009: The best thing happened to me was walter lewin lectures. I passed class 12 without physics and chemistry teacher (govt school and the teachers got transferred). I wasn't even aware JEE, AIEEE existed. I did bad in competitive exams. Suffered through bad education for 7 years to get a well paying job. Now the dust is settled after almost 10 years, what am I doing? Going through all his lecture along with lot of mathematics once again and getting all my education fixed. And it is a treat!
I was convinced with faraday's law since 2009 (the demo blows me even today). Mr. Lewin, your lectures saved me. They taught me how to reason through slowly and to believe reason over gut.
:)
I do not understand a single piece of this whole discussion, I'm just a regular software developer with no background in physics or math. But I do love physics and science in general and I do have a huge respect for both central figures here, Prof. Dr. Lewin and Mr. Sadaghdar.
I just wanted to say that such discussion is beautiful. I can imagine things like this happening at the London Royal Society between respected and beloved science fathers of our past, and that's exactly how science is and should be made. Hundreds of scientists are following this discussion as it happens, each leaving their respective perceptions, I'm amazed.
Thank you two for all respect and time put in place here.
And thank you everyone who is trying to help them out.
*ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law and he also tries to imply that a modern version of KVL is identical to Faraday's Law. That is a joke, see my video 5 + 3 - 8 = 0. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
@@lecturesbywalterlewin.they9259 I watched his video. In no way it was harassment. He even pointed out multiple times that he is just a guy with a diploma on TH-cam and that you are a renovated professor and that he is most likely wrong. He presented his points very objectively and without saying a single bad word about you. Let alone discredit you. These words you have for him are very rude and disrespectful.
If you disagree with him why don't you just objectively point out he is wrong? Instead inducing all this drama. You are a professor, sir, act professional.
@@ilmu011 I have pointed it out!
*ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
Thank you Dr. Lewin for acting more collected and calm in your demonstration today as opposed to last week. It is far more professional and appropriate if trying to get your point across.
You are debating terminology and for some reason discriminating against induced voltages, for some reason saying that we shouldn't include induced voltages in using KVL. Let me ask you this. If you were designing a circuit that took mains AC voltage from your wall, would you include the voltage supplied by the mains (120V or 240V or whatever) in your sum for KVL? If so, why? By your argument, induced voltages shouldn't be counted. That voltage is only there because of a changing magnetic flux through the secondary winding of a distribution transformer. But maybe we don't have a transformer in the mix. Maybe you're running your house directly from a local generator. Well then that mains voltage is due to changing magnetic flux in the windings of the generator, so why are you counting that? Your determination to discriminate between electromagnetically induced voltages and other voltages is entirely arbitrary. Faraday's law tells us how to determine a voltage due to induction if we know the rate of change of magnetic flux, just like Ohm's law tells us how to determine a voltage across an ideal resistor if we know the current and resistance.
I watched the video
ElectroBOOM's major issues are related to KVL and Faraday's Law and to my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values *(as they should according to Faraday's Law).* It is clear from his video that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight. He has a masters degree in EE. His video is therefore an embarrassment.
watch this too: th-cam.com/video/ototTU5NUNA/w-d-xo.html
@@lecturesbywalterlewin.they9259 But professors introduce and teach this thing, this "new form of KVL" in universities. I am EE student too, and they taught me the same way. This is written in books. We say, the voltage of an inductor is L*di/dt. :/
By the way, thank you for your response, and keep doing physics!
@@susceptibility_ This "new form" is just a conversion of Faraday's law. It is like don't understand Faraday's Law and write it in a wrong way and say it is a "new form". IT IS NOT ACCEPTABLE!
@@feinburger244 Indeed the "modern" version of Kirchhoff's rule is Faraday's Law.
Thank you mr. Lewin. Great video and the shirt is amazing too! Could you please actually watch Mehdi’s video and reply AFTER you watch it? This gesture will be greatly appreciated by A LOT of people (Mehdi has 2M subscribers). Mehdi is nowhere near you at theoretical physics, this is exactly why we all would love to hear the explanation from you about his experiment and what he made wrong in it. He in no way is doubting you, but rather wants to know whether he is wrong and if so, then what the mistake is. It is a bit embarrassing that in order to have a simple question addressed we have to chew through the chinese wall of teachers Ego first. YOU DID NOT EVEN WATCH HIS VIDEO. 🤦🏻♂️ Isn’t this an ignorance? This is not how science is done, this is how religion is done. By not watching his video you immediately leave science area and go into a religion area. I can see how a professor of your age can be embarrassed by this situation, but please tame your wild ego and give a legit analysis of his mistake, if you are so sure that there is one. We all will only appreciate that gesture and it will make you look much better in front of 2000000 people, not only 100-1000 students.
He did watch his video. Don't jump to conclusions. EB doesn't seem to understand Faraday's Law.
@@nahiyanalamgir7614 I'm a bit late to the entire thing but lolno. It's pretty clear that he did not watch EBs video before making this.
in other words: Kirchhoffs law (*1845) doesn't care about magnetic fields at all. Maxwell's equations (*1864) 19 years later do. To use Kirchhoff's Law to describe circuits with changing magnetic fields, you have to use "something" that is only described by Maxwell's equations.
This "something" combined with Kirchhoffs law is **Faradays Law.**
So from the Physical Position Dr. Lewin is absolutely right.
I think the biggest problem is the communication between very practical and theoretical people. Often if someone is very deep into something, he/she has a hard time understanding the problems of people in other holes.
Absolutely correct!
you got the point
EB is more of an engineer. Dr. Lewin is a physicist.
"he said I did bad probing, so like a 5yo I lashed out, tried to silence him by telling him to get educated"
A manchild with a large ego. May be an intelligent individual in some aspects of reality, but he isn't really a "smart" individual in social terms.
Can't even act like an adult when questioned.
I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values. th-cam.com/users/th-cam.com/video/nGQbA2jwkWI/w-d-xo.html
This can also be demonstrated with a transformer.
th-cam.com/video/b7i2uMx7gHo/w-d-xo.html
The reason is that an induced EMF (Faraday's Law) creates a non-conservative E field. This means that moving a test charge between the same 2 points in a circuit can require a different amount of energy (even with opposite signs!). You still aren't getting any energy for free, because it comes from the source of the time-varying magnetic field.
When a voltmeter reads a value V it means that the integral of E dot dL across the voltmeter is V.
In cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value. Kirchhoff's original text can be found in the following link, pages 497-514: books.google.de/books?id=Ig8t8yIz20UC. Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.
My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics. This demo has now become a classic; it's done all over the world at many colleges and universities.
*ElectroBOOM and Dirk Van Meirvenne believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true.* They each posted a video on their channel in which they claim to have proof for their wrong ideas.
Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT. freepdfhosting.com/0813df09f5.pdf
*ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly both voltmeters would have read the same value. He could not have been more wrong.*
The following video may also help some of you to understand why 2 voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html I thank Mick Vall for his insightful comments.
thisis a mini lecture which address allthe key issues. I cannot improve on this. I therefore send it to all who have a misconception about Faraday's Law. I could alse have referred viewers to a page in then Feynman Lectures which would then be equivalent to what you call copy and pasting.
Beautifully explained. Let’s hope this is the last time you need to comment on this topic.
I think here we are an example of the typical conflicts between a physicist and an electrical engineer point of view
This obviously relates to your video where you have two voltmeters connected to the same two points, and the voltmeters show different results. I suspect that many people who have asked you questions, such as myself, are perfectly aware that KLR applies to steady state circuits. No argument. However, for the voltmeters to read differently, even though connected to the same two points, something about their position in space must be the cause. If we consider the voltmeters to be moving coil analogue devices, then the thing that makes the needles deflect is a flow of electrons. In this experiment, it will be a pulse of electrons. In the setup chosen, voltmeter V1 will get a different magnitude pulse, and in a different direction from the pulse in V2. If the connecting wires have no flux change through them and they have negligible resistance, then many of us struggle to see how this can happen. We can extend the wires many metres from the resistor and whatever is changing the flux, we can surround the resistor circuit in mu-metal, all sorts of variations. Surely the only thing that can give your result is a difference in a) where the wires are arranged and b) different flux changes in those wires.
When I taught physics there was a standard problem of an aeroplane with metal wings and fuselage, flying through the Earth's magnetic field where the field was at an angle to the horizontal. This would induce an emf between the tips of the wings. The students had to calculate the emf. Simple. But then I would ask them, could they think of a practical way of measuring this emf to check their answer. Most would say yes, hook up a voltmeter in the fuselage with wires extending down the wings. I would then ask them to consider what effect there would be in the connecting wires as the wires passed through the magnetic field also. Great fun!
There are different readings when the Voltmeter wire is on either side of the loop because the wire is enclosing the flux from different sides and in each case the resistor in the path restricting the current flow and causing it to take the route into the voltmeter is a different value.
Prof. Lewin you succeded in a very special way. You are the only man I want to listen, even when I don't understand, what he tells me.💖
you are so kind
@@lecturesbywalterlewin.they9259 I don't want to disturb your lectures. But have you ever heard about Theo Jansens wind sculptures on beaches? They are Physics in action. I love the winds, because I'm from the North, but more I love you, Walter Lewin.
@@mimisunny1820 yes I know his work very well. I have seen a retrospective of his work in the US and I have seen some of his sculptures being blown by the wind
@@lecturesbywalterlewin.they9259 I hope, you enjoyed it, I nevr saw his work in reality. But because of Faradys Law I can post it here. It is a kind of art, I really adore. Because it is fragile et dynamic. And I hope you will have a very beautiful winter again.
th-cam.com/video/LewVEF2B_pM/w-d-xo.html
yes I remember the piece on the video. I saw a video of it at the exhibition.
If you are going to argue someones point, you first need to listen to and understand that point, or else your argument is completely invalid. You, sir, are invalid.
He watched his video and responded to it perfectly.
I wish people removed the dislikes they have given to this video. This is a very fine explanation of what is being disagreed upon.
This is by far the best and most concise explanation about KL RULE and Faraday’s LAW I have ever seen. I am so using it in my lectures.
:)
The book by Purcell at least agrees with you. At page 359 (3rd edition), "A consequence of Faraday's law of induction is that Kirchhoff's loop rule is no longer valid in situations where there is a changing magnetic field."
At page 366, he treats the RL circuit by counting all the "ohmic components" on one side of the equation, and the "induced EMF" on the other side (which includes the inductor) of the equation.
Then he points out that you can count the inductor as an element by itself by *defining* "voltage across the inductor" to treat it like the other elements.
Yes Purcell, ofcoz Purcell would not make that mistake neither would Jackson and I suspect that Griffith also has it correct.
"At least" ?!, I really falled in love with purcell book, and griffiths books about electrodynamics. I consider griffiths,jackson,purcell,landau the holy squadbible of electrodynamics.
And I consider Purcell a great physicist because he can explain any really fancy hard thing in very intuitive way just like the great Mr. Feynmann.
@@lecturesbywalterlewin.they9259 Professor Lewin, I just decided to purchase Purcell's book and abandon Giancoli. Such a disgrace to make such horrifying mistakes that affect readers!
I think these equations below can help everyone to understand.
e=-Nd¢/dt, e=-Ldi/dt
So, i can say ¢=Li
¢=magnetic flux.
i=instantaneous current.
L=inductance of the path
e=induced emf.
N=number of coils.
note N=1 because it's only a coil having single turn
You guys need to understand that when the magnetic flux changes, a NON-CONSERATIVE Electric field is also induced. That is why changing magnetic flux is able to induce currents, an electric field is present that does work on the charges and moves them.
Kirchoff's Voltage Law for the Electric Potential at a point in a circuit is fundamentally based off of the Law of Conservation of Energy. It assumes that the energy that goes into moving the charges around a closed loop circuit is conserved. You can't have a circuit with conserved energy when outside effects (changing magnetic flux) are creating fluctuations in the current of the circuit. Thus, Kirchoff's Law only applies to the special case where everything is conserved and isolated. This is not representative of the real world because magnetic flux is constantly changing in almost all of our electronic related technologies.
This is Professor Lewin's main assertion, from what I could gather.
Finally a non-EB-fan who is able to understand this simple concept.
I was taught of KVL as "the sum of voltage rise and drops across a loop is zero". I guess this is more apt definition. And the EMF induced can be incorporated as voltage rise or drops.
Sir pease do talk on these forums. Really thanks a lot for making this video. But please do consider Mehdi Sadaghdar, he complains more about the wrong probing used.
And allow me to disagree, but I really think the self inductance of the probing are missing from your equations (I might be completely wrong). Though Mehdi says that KVL always works, he doesn't say that Faraday's is wrong.
And regarding sir not talking on the forums (comments section), sir please do discuss here. Mad people always keep saying different things. But the genuine and true curiosity, hunger for Physics should not go unsatisfied I feel. And all aspects of Science only advance and become more clear after disagreements, discussions and experimentation. So please do talk here in the comments section.
The sum of voltages form is what you get when you apply the integral form of KVL to a circuit diagram. Adding ad hoc corrective terms is good engineering, but it is essentially just admitting that the model was wrong to assume KVL.
Yes Professor Lewin is correct. For a d.c. transient current, during this short time when an inductance L component (solenoid) is present since it has inside a 3D field with dφ/dt monotonically changing Kirchhoff''s law is not holding. Kirchhoff''s law however is holding in an electric conductor circuit after the transient is passed and a stable D.C. current is flowing inside the circuit.
Kirchhoff''s law is also holding for stable alternating a.c. current conductor circuits because the dφ/dt is not monotonic.
:)
Saying someone has a religious belief in something just because they went through the trouble to experiment themselves and discovered that your experiment was flawed, is sad and pathetic. your thinking is dogmatic
You are demonstrating the fanaticism he's talking about. If you are talking about ElectroBoom's demonstration it's because its flawed.
Walter Lewin religiously believes that some people religiously believe in Kirchhoff's loop rule.
It might be dogmatic, But at this point he actually showed why KLR does not always work. As you could clearly see, KLR holds if and only if, there is no changing magnetic field.
watch full video in the end of video prof say i will answer in next video you guys are electroboom fans and believe what electroboom tell you
i'm not saying prof lewin is right but electroboom fans are saying electroboom is right
@@Theo0x89 this could become the Walter Lewin's Loop Rule
It's going to be an infinite pain for us, at least until all of them will agree to just use faraday's law when it's needed
I think the problem happens because people define the problem differently. I think what KVL means is that in a closed wire that has reached equilibrium with a steady current, the energy gained by the charges flowing must be equal to the energy lost by it. This is a consequence of our assumption that the current is steady and the system is in equilibrium. Faraday's law just gives a measure of the energy gained by charges in a loop when there is a changing magnetic field. If there is no way for charges flowing in a loop to lose that energy (like a resistor or maybe in radiation), the charges would accelerate and the current would keep increasing and a steady state will not be reached. This does not happen in a typical wire where a steady state would be reached in a fraction of a second and the charges flowing in the wire would lose the equivalent amount of energy they gain and hence KVL would hold in general. I am an electrical engineer and I am not sure if what I say is always right but that I what I think.
Remember the case when an ideal voltage source is connected to an ideal capacitor. At the instant, when the circuit is closed and there is no charge on the capacitor, KVL would not hold because the circuit has not reached steady state.
The point of argument of ElectroBoom and Professor Lewin is technical. Boom refers to points in a conductor circuit where the path of electric current is fixed and the same for both voltemeters whereas Professor Lewin refers to points in fields and fieldmeters without any current really induced between these points (fieldmeters are usually fluxgate or Hall sensor). A normal current induced voltemeter can not be used in the second case. Boom refers to potential measurement by measuring electric conductor circuit current and Professor Lewin to direct measurement of electrostatic emf in a field (air) without electric current produced. In the case of a field measurement even the slightest misalignment of the meters from a predefined in space location and position (a few degrees) will change the path and give a different reading due the charge interactions within the field.
In a nutshell Kirchhoff's law applies for electric current conductors circuits and not for Electrostatic fields.
But yes if the path is exactly the same meaning not only in lengh but also in 3D spatial orientation the measurements will be the same under the same conditions in a 3D field.
Sometimes electric engineers and physicists are saying the same things but in a different language. :)
Markoul
Electrical Engineer
p.s. the best experiment to see this effect is to use a dc magnetometer. The slightest movement will change the reading.
The only problem arises while not understanding the difference between conservative and non conservative electric fields while considering circuits having changing magnetic flux induced fields are non conservative they dont add up in KV loop coz potential energy for them cannot be defined, Hence I totally agree Faraday's Law is the fundamental law to go with and not KV loop law..👍
Great to hear you are going to go over your famous two voltmeters / two different readings experiment. I'd like to be able to do this experiment for myself, and working from memory here, I seemed to recall one or two technical details left me short of feeling I could do so. You may have just resolved that. I always wanted to check my understanding of that historic lecture by posing the question: 'to be clear, are you saying that the reading is voltmeter position on the bench dependent ?' - well to day you explicit told me YES. And that is great. I'm mathematically trained so when you discussed the non-intuitive aspects of path independence in conservative fields I was straight on board. But what didn't come across from the lecture, a difficulty because of working in 2d i think, is what the differing paths where ?
Anyho. I hope this feedback contributes something and look forward eagerly to your next video.
engineer vs physicist got real
There was actually a similar question in our physics exam, which asked us to state whether Kirchhoff's loop rule is valid in AC circuits. Although I got the answer right, it was really helpful to get a proper reason from you. Thank you so much, Professor. Wish I had come to know of your channel earlier than I did.
:)
Dr. Lewin, Sir, I wanted to tell you that I bought your book and I love it. I've read it over and over so many times. Currently, I'm a missile engineer for US Navy. I have an EE and MS in Optical Engineering from UNC-Charlotte Institute. I watched all your lectures and applied many of the concepts in your 801, 802, and 803 to my work. Thank you, sir!!!
:)
Thanks Prof Lewin. Having watched all of 8.02 and read the lecture notes that video was clear for me.
:)
I've found the mistake in Freedman on chapter 30 which talks about inductance
In my portuguese version of the third volume entitled "Electromagnetismo" , page 349 , after they derive the equations it says:
"Assim justificamos o uso da equação 30.8 (the differential equation) na lei das malhas de Kirchhoff para a análise de circuitos"
In fact they use multiple times Kirchhoff's loop rule throughout the chapter.
I can't tell if they used it correctly or if they made the same mistake all over the chapter. (I'm worried because I always tought Freedman was a great base college physics)
But now I know the book has it wrong.
Thank you Dr.Lewin from Angola.
:)
Sir thank you for your special effort you put in whenever you explain Physics (so much better than just a mediocre effort to explain them). But also please respect everyone have different abilities in understanding - please don't laugh at them.
Hello Peter. I was insulted by 2 viewers. They argued that 2 voltmeters attached to the same 2 points in a circuit always MUST show the same value. They broadcasted on their youtube channels that the reason I measured 2 different values was due to my incompetence "my bad probing". Here are the facts:
*I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html
*Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.*
*My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.*
*Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.*
*By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.*
Thank you for this explanation this really helped me with my conceptualization of maxwells equations
You're very welcome!
Thanks, Doctor. I have a lot more studying to do. I have always thought Kirchhoff’s laws hold, but that’s because I’ve only applied KVL and KCL in the special case. I work with “magnetics” in my job, but luckily for me it’s possible to design a good, efficient transformer without actually fully understanding Maxwell’s equations. The V, R, L , switch circuit you analyzed is exactly what I deal with on a daily basis in switching power supplies, except R is virtually negligible and the switch is a MOSFET. I’d feel a lot better if I had a better understanding of Maxwell’s equations. I think I’ll watch your lectures again, and this time, I’ll read the notes and work some experiments myself. Thanks again. My learning curve is steep, but hopefully I’ll get there.
While I agree with the comments that the way electrical engineers use KVL is usually correct I also agree with Lewin that their underlying reasoning if not wrong then at least is misleading in the sense of the correct understanding of the underlying physics. Moreover his demonstration showing that voltmeters attached to the same pair of points can measure different values proves how careful one has to be with the assumption that a circuit consists of only lumped elements that being the most basic assumption when one applies KVL and KIL. I also want to emphasize that all viewers should be grateful to Lewin for pointing out this problem, it cost them nothing to watch and learn from him. And instead of whining about the manners of an 82-year old man that are irrelevant to the question/problem, if they do not like his style they do not have to watch it, just skip the video; he owes them nothing.
Late to the party but Professor you are absolutely correct! It's a shame how many so-called "experts" don't even have a clear understanding of the basics and still feel qualified to act as an "educator". This is not politics or sociology, this is physics. Classical physics that has been backed up by numerous experiments and real-life applications and distilled by great minds such as Faraday and Maxwell. To agree or not to agree is not the question.
Ms lewin the winer absolutly 😎😎😎 i'll do this expirement in my home 👲👲
It is just a misunderstanding between "physicist " and "engineers". Physicists look at the circuit as a physical structure in the real world with elements are placed in it as being in the real world. In that case, the EMF is an extra source that is considered by Faraday law. But in the engineering world, we are working with a model of the physical system and the EMF induced in the circuit is modelled by an extra "inductor" element. The KVL is correct for the model and it does not hold for the actual physical circuit so if you correctly model the circuit the KVL is correct " in your model". The problem here is that Prof. Lewin is using the real representation of the physical circuit and thinks the KVL is not working there which makes sense because it is used in the wrong context. BTW this type of modelling and adding extra inductor is a simple tool that any engineer is using on a daily bases for modelling "electrical machines" and I believe it is due to different type of education and mindsets that physicists and engineers sometimes cannot understand each other.
ha ha ha 5 + 3 - 8 = 0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html
I love your way of talking about physics and I highly respect your work. by the way there is some differences I have to mention:
1.the kirchoff voltage law isn't integral of electric field on a closed loop but it's the sum of the voltage differences around a closed loop. and these two are different.
2.according to the kelvins law we sum all of the voltage drops or gains in a closed circuit so we add that inductor voltage too. and of course if we want to analyse faradeys law we have to assume that the magnetic field is passing the whole circuit not the inductor.
edit:
to make it more simple kirchoff law is actually saying that any voltage produced in a loop would consume by something in thay loop so the energy conservation law does hold that way
Exactly. KVL is NOT the closed integral of E.dl. I don't know where did they get this from. Surely not from Gustav Kirchhoff.
Integral of E.dl = work done , which has units of energy. When Integral of E.dl = 0, that means work done along the closed loop = 0.
What is the work done to move the current through each component of the circuit? By definition its voltage*charge.
Sum (voltage*charge) = 0, since the same charge flows in the same circuit.
Sum of voltage = 0 , which is KVL
@@iLoveTortex >>>Integral of E.dl = work done>>>
*that is incorrect* VA - VB is the Integral of E.dl in going from A to B.
*integral of E.dl is NOT energy*
The sum of voltage differences form is exactly what you get if you apply the integral equation to the circuit diagram. The two are not distinct things.
This is such a good explanation. Thank you very much Professor. Anyone who thinks that Kirchhof loop rule always works has to realize that such a thing means that Maxwell's 3rd equation (Faraday's law) is wrong. And such a thing is complete nonsense, and like you said, everything in physics and engineering would fall apart. Faraday says that "integral of E dot dl can be any value", but Kirchhof's loop rule says that "integral of E dot dl can only be 0". They can't both be true. So Kirchhof's loop rule is true IF AND ONLY IF "dphi / dt" is 0. That is like saying that "a + b = 0" is the same thing like "a + b = x, where x can be any number", meaning "a + b = 0 and a + b = 24 at the same time", which is complete nonsense.
:)
people should understand that in science, we work with the experiment and conclude something.
based on that conclusions we draw models that fits the conclusions.
but going in the reverse direction is completely foolish.
One question still remains.
Which one is the real Kirchhoff's law?
Closed loop integral of E.dl = 0 (KVL according to Walter Lewin, which sometimes holds)
Or
Directed sum of voltages around a closed loop = 0 (KVL according to electrical engineers, which always holds)
Clearly, the two are not equivalent, since one can measure the voltage across an inductor when the current is changing and it won't be zero, while E.dl will be 0.
Kirchhoff's loop rule (KVL) is older than Faraday's Law.
To now introduce a "modern version" of KVL which is really Faraday's Law is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html
This makes me not want to continue in electrical engineering....my freaking head hurts listening to all this.
Your head shouldn't hurt, you are an engineer. You worry whether it works, not why it works.
I like how he puts his hands together to think "how do I reach these kids".
I wonder if electricity is somehow like physics and quantum physics. Or perhaps all other laws actually doesn't always work, we just haven't found the situation/condition where those laws we knew didnt apply?
Magnetism can only be understood well with QM apart from the fact that it is also the result of SR (Read chapter 5 of Purcel's book).
Here's the answer:
If inductance of wire is considered, which means "in the varying magnetic field, wires don't always have zero potential difference across it" is considered, then Kirchoff's law would be right.
However, if you insist that in Kirchoff's law, the inductance of wires are not considered, then KVL does not apply.
And that would be plainly a difference in definition of Kirchoff's law, and I personally don't think Kirchoff's law have the restriction that inductance of wires cannot be considered.
If you intentionally "ignore the inductance of the wire and the induced voltage difference across the wire" and "claim that even under this practical case we shouldn't add a 'virtue inductor' in the circuit to symbolize the inductance of the wire", then you successfully defies your "simplified" version of KVL.
Nevertheless, I would consider the "virtue inductor" an appropriate model to be implemented just as we treat "internal resistance" of cells as a "virtue resistor" in series with the original cells since it helps us better mimic reality in our circuit diagram.
All I know is the probing wire generates an opposite voltage to what you where trying to measure, just do to its positioning.
Watch ElectroBOOM's video, Its not like you'll get electrocuted while watching it.
I watched it
*ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
ok never mind, sorry for bothering you.
when an inductor is involved and current is changing, KVL doesn't work because of magnetic field energy storage in the inductor. It is as if voltage disappears, and it comes back as the current begins to decrease. KVL works fine when current is steady.
So "For the birds" = "Just a specific case" ?
Yeh just a Dutch saying. Just like "you can't make chocolate from this"
I think he is just frustrated that so many people insist on using it in cases where it is not applicable and still state it like it is a fundamental law of nature.
Sir, you are awesome!
It's a great pleasure to be able to experience this time on Earth and learn from your lessons and your deep knowledge about Physics. Science works and people need to be educated.
His classes have helped me both in the understanding and willingness to learn physics and in my personal development, today, I am a teacher, trained in physics and mechanical engineering because of you. I wish all the best for you and continue with your work until the last day, you are a special person.
Obs:
I bought your book and it will be coming to my house soon. Super eager to read it. :)
:)
Thanks Prof Lewin. One of the big problems in teach physics is teaching the wrong concepts, rule vs law, KLR is a rule not a law and Faraday is a law of nature.
So basically this whole problem/feud that raised a lot of unpolite responses and even racist remarks, just because a different definition of one Kirchoff Law, is it the loop rule or voltage law, I don't know. But weirdly both of the guys agree, that if you have the inductance of the loop considered the sum of voltages would equal zero, just that one calls it the faraday law and the other calls it MKVL...
Was this a real thing? People did call themselves frauds and went full racists because the name of the rule, even though both agree that change in magnetic field will produce an emf?
I do admit that I was impressed with the experiment results, and was a really cool, but not cool enough to justify racism and all other types of name calling...
Hi DR. Lewin - I have an easy experiment that show that KVL does not always work; and other experiment that show that Faraday’s Law also sometime doesn't work , but using KVL law we can solve problems even in the case that Faraday’s Law does not work. Sound a bit fantastic but can easily explained
(1 Trasmition line (KVL can't explain it ) 2) Bi-Polar transistor (Fraday's law can't explain it) 3) Bi-Polar Transistor lumped model in the conduction region can be solved w KVL.
- I can provide full answer in email . As EE eng I agree that KVL is special case of Faraday’s Law BUT I do not agree that KVL is useless. on the contrary for engineers KVL is much more practical for use and solve complex problem relatively easily than to use Faraday’s Law. It is not a matter of belief - engineers "make" KVL to "always work" by a change to the problem
*I appreciate the fact that this Physics may not be familiar to you. Don't feel embarrassed about it; you are not alone. However, it's never too late to get educated. The choice is yours. Maybe this will help you.*
*I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html
*Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.*
*My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.*
*Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.*
*By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video (see @ footnote below) on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.*
*Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT.* core.csu.edu.cn/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/C29636DB-AB80-49E0-BFAB-BCE00159F00E/0/lecsup41.pdf
*(@) ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly I would have found that both voltmeters would have read the same value. He could not have been more wrong*
*This is my only msg on this issue. This is too basic. "I teach physics, I do not argue with people who think they know but who don't" (quote from Neil deGrasse Tyson). I do not argue either with people who believe that the Earth is flat.*
This video may also help some of you to digest why 2 Voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html
*Below follows Problem 7.50 in Griffith. Notice the drawing which he copied from Romer and he wrote: "Notice that V1 is not the same as V2, even though they are connected to the same points! See R.H. Romer, Am, J, Phys.50, 1089 (1982)"* drive.google.com/file/d/1G1a8_YNvB8X9xddUD27x9PE-j7Xbfo3m/view
You have failed to address the raised issues again. The main one is your faulty measurement methods which leads you to believe that 2 voltmeters connected to the same point can read different values. If your setup induces a current on the voltmeter leads and you get different results depending on where the leads are positioned, that means your measurement setup is invalid. Because in such a case you will not be measuring the voltage accross point A and B. The voltage accross A and B will be the same with any number of voltmeters if you know how to probe right. You are ABSOLUTELY WRONG to state that the voltage is undetermined. Please think about this point and explain it clearly.
>>>> The main one is your faulty measurement methods which leads you to believe that 2 voltmeters connected to the same point can read different values.>>>>
*Get educated.* Watch my 8.02 lecture #16 and the video which I will post today or tomorrow and look at the article written in 1982. www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf
Think clearly when you say "voltage between A and B". When there is a changing magnetic field, the voltage measures depends on the path of the probe right?
So a unless you create a convention on the path measure the voltage, it is indeed undefined. This is especially true when there are people working with plasma that simply cannot use the circuit model! Of course engineers who deal with circuit everyday will set up a convention to probe the voltage along the circuit but that is by no means should be treated as definition of voltage.
@@wmh829386 I guess we disagree about the definition of Voltage there. What if we measure the voltage with shielded cables? If the probes are affected by the field, the measurement is simply invalid. Furthermore, it is possible to calibrate the probe to remove its effect from the measurement. Dr. Lewin may be a good educator and physicist but he is wrong here. The conclusion that the voltage is undefined is wrong. We can put this circuit in a EM simulator and calculate the voltage at any point and time.
Happy Birthday! Dr. Lewin.
I know first hand! The alternator in my car died! What I wouldn't have given for a non-conservative field in that case... :)
A great video and the commentary was a good read. We love You Tube and every thing about it.
We believe in physics. That's all.
@TheSearchingTruth Physics works - if not we would not exist
KVL does work iff you take the closed loop integral of the ELECTROSTATIC FORCE, the conservative force , excluding any contribution of the induced electric field.
*I appreciate the fact that this Physics may not be familiar to you. Don't feel embarrassed about it; you are not alone. However, it's never too late to get educated. The choice is yours. Maybe this will help you.*
*I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html
*Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.*
*My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.*
*Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.*
*By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video (see @ footnote below) on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.*
*Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT.* core.csu.edu.cn/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/C29636DB-AB80-49E0-BFAB-BCE00159F00E/0/lecsup41.pdf
*(@) ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly I would have found that both voltmeters would have read the same value. He could not have been more wrong*
*This is my only msg on this issue. This is too basic. "I teach physics, I do not argue with people who think they know but who don't" (quote from Neil deGrasse Tyson). I do not argue either with people who believe that the Earth is flat.*
This video may also help some of you to digest why 2 Voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html
*Below follows Problem 7.50 in Griffith. Notice the drawing which he copied from Romer and he wrote: "Notice that V1 is not the same as V2, even though they are connected to the same points! See R.H. Romer, Am, J, Phys.50, 1089 (1982)"* drive.google.com/file/d/1G1a8_YNvB8X9xddUD27x9PE-j7Xbfo3m/view
*Science is always TRUE whether you believe or NOT ! - Neil Degrasse Tyson*
*Physics works and i'm alive - Walter Lewin*
🔰 Can anyone answer my questions...
A) Is Dr. Levin saying that the ‘DC’ current passing through the inductor, (in an instant) is producing a changing magnetic field
OR (I think I’m asking the same thing)
B) Is he saying that from the time the DC current initially starts to flow until the peak voltage occurs, that in this nanonano second, that there’s a changing magnetic field, and therefore there is an initial voltage present it’s just that we can’t see it❓
C) Is Dr. Levin saying that the voltmeter is reading a voltage across the inductor (coil) and we just can’t see it, because of the voltmeter’s circuit❓
D) Is he strictly speaking to DC current❓
flow of inductor current is constant and not changing such as in a steady state DC current, then the induced emf voltage will be zero because the instantaneous rate of current change is zero, di/dt = 0.
✔️ This is from a well known website...
Is Dr. Levin saying this is wrong ?
“With a steady state DC current flowing through the inductor and therefore zero induced voltage across it, the inductor acts as a short circuit equal to a piece of wire, or at the very least a very low value resistance. In other words, the opposition to the flow of current offered by an inductor is very different between AC and DC circuits.”
www.electronics-tutorials.ws/inductor/inductor.html
Forgive my lack of understanding...
watch my 8.02 lectures and get educated
Lectures by Walter Lewin. They will make you ♥ Physics.
Thanks Dr. Lewin,
I feel honored to have you reply to me❗️
Prof, Thanks a lot for your warm heart to inspire us
My friend and me, he studied electronics, were doubting the last video, understanding electrobooms explanation. But this one is completely clear. in fact i had never head of KLR in integral form.
Can you explain what Medhi's mistake was?
damn Lewin always wins the man is a g
Well ... what does an inductor " fighting a changing current" even mean in electrical terms ? Imho at t=0 there is no current because the voltage over the inductor is minus the battery voltage, leaving 0 V over the resistor. KLR intact. That's how the inductor "fights" the current. I don' t understand where this idea from the professor that there can be no voltage over a perfect inductor originates. It makes no sense. Imho the professor has a religious belief that there can be no voltage over a perfect inductor. ( I hope you do not consider this rude professor. Your have a 99 % credit of correctness in all other cases which is kind of neat ).
Anyway, I'm not religious and certainly not in this case. If the professor actually is right I do hope he convinces me as soon as possible and it will be the happiest day of my life. Really.
What in the case the current has reached the maximum or lets say 99 % and the switch is opened. In my experience a huge voltage spike will follow. Infinite in theory but limited by various non perfect factors. For example sparks will form between inductor terminals. But I guess the sparks will form a loop where KLR will check out according to the professor' s explanation. But why do they start in the first place ?
It's interesting to realise that the professor cannot be proven wrong by experiment. If measuring over the inductor with a voltmeter proves nothing because it forms it's own loop then there cannot be proof of voltage over the inductor. Like Schrodingers cat. If we do not measure the voltage ( or open the box ) does it mean anything to say there's a voltage ( or a living cat ) ? I guess not ..... Maybe there's a clue there :-).
A perfect inductor is made out of nothing but superconducting wire. In a superconductor, no energy is dissipated and so no electric field can exist inside a superconductor. A changing magnetic field doesn't induce an electric field into the inductor, it adds curl to the total electric field, so it is no longer a conservative field. The notion of voltage over the inductor becomes path-dependent and therefore is ill-defined.
_"what does an inductor " fighting a changing current" even mean in electrical terms ?"_
Lenz's law says that the changing magnetic field induces an electric field that "fights" the change of current.
_"I don' t understand where this idea from the professor that there can be no voltage over a perfect inductor originates."_
As you can see in the video, there is a voltage over the inductor in the sense that a voltmeter measures a voltage. But the line integral over the electric field along the windings of the inductor is zero. That's all there is to it. Walter Lewin believes that Kirchhoff's law is about the line integral, while people who actually analyze circuits in real world application use the real Kirchhoff's law, which is about the measured voltages over circuit elements like the inductor.
_"sparks will form between inductor terminals [...] why do they start in the first place ?"_
Again, Lenz's law says that the changing magnetic field induces an electric field that "tries" to maintain the current, creating a huge voltage.
_"If measuring over the inductor with a voltmeter proves nothing because it forms it's own loop"_
Well that's the big question here. If it is possible to arrange the probe wires so that all induced voltages in the wires cancel, then you can test Kirchhoff's law experimentally (the real one, not Lewin's).
"Imho at t=0 there is no current because the voltage over the inductor is minus the battery voltage, leaving 0 V" - agree with that, and that determines the slope of the rise in current. The rise in current will such as to create a voltage across inductor equal to that of battery. In the next moment, when there is some current, the rise in current will be smaller, as some voltage will be reduced in the resistor, and inductor will need lesser voltage over it to hold KVL. Following this logic moment by moment, you get the LR curve shown in the picture, and at each instant you use KVL. (I don't know if KVL hold in general, that's WAY beyond me, but for an LR circuit with DC or AC, from every EE textbook and computer simulations, it holds for sure.)
But that is wrong. The voltage over the inductor is not the negative of the battery. Were you not listening when the professor said it is a superconducting inductor?
You are basing your answer on nothing, while the professor is basing his answer on the physics of superconducting wires. Who is the religious fanatic here? You or the professor?
Also, this video clearly shows in the first minutes why Kirchhof's loop rule DOES NOT WORK. Both Kirchhof and Faraday can't be right at the same time, because one says that integral of E dot dl is always zero, and the other says that it's not true, and it can take any value.
Faraday's law is part of Maxwell's equations, and if you are not insane, you know Maxwell's equations are true, hence Faraday is true, hence Kirchhof is false. End of discussion.
If a + b = 0 and a + b = 12 (or any other number) only one can be true. I hope that is obvious. If the first is equivalent to Kirchhof and the second to Faraday, and if you believe Maxwell's equations, the first one is the false one. If you disagree, you are disagreeing with every physicist ever, not just the professor. Maxwell's equations are solid.
@@photonenbremse: Absolutely no energy is dissipated in a perfect inductor. But there is voltage as long as there's increasing current. The case is that the energy fed into that inductor is converted into a magnetic flux. Not dissipated. When the switch is opened the magnetic flux will decrease and the energy will come out in the form of a high voltage spike with a high impedant load when sparks may form. If its terminals are connected with a resistor the energy will be dissipated in the resistor. If it's shorted with another superconductor no energy is dissipated and the magnetic field will persist as does happen in the superconducting inductor in an mri machine..
Sounds like a disagreement in the definition of KLR
*I appreciate the fact that this Physics may not be familiar to you. Don't feel embarrassed about it; you are not alone. However, it's never too late to get educated. The choice is yours. Maybe this will help you.*
*I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values.* th-cam.com/video/nGQbA2jwkWI/w-d-xo.html *The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.* th-cam.com/video/b7i2uMx7gHo/w-d-xo.html
*Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.*
*My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics.* *This demo has now become a classic; it's done all over the world at many colleges and universities.*
*Kirchhoff's original text can be found in the following link, pages 497-514:* books.google.de/books?id=Ig8t8yIz20UC. *Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.*
*By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures.* *They each posted a video (see @ footnote below) on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations.* *Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path.* *MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake!* *I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.*
*Also read Professor John Belcher's thoughts on Faraday's Law and on KVL. Professor Belcher is my former colleague at MIT.* core.csu.edu.cn/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/C29636DB-AB80-49E0-BFAB-BCE00159F00E/0/lecsup41.pdf
*(@) ElectroBOOM insulted me in his video by mentioning that the reason why my 2 voltmeters read different values was due to "bad probing". He stated that if I had done the demo correctly I would have found that both voltmeters would have read the same value. He could not have been more wrong*
*This is my only msg on this issue. This is too basic. "I teach physics, I do not argue with people who think they know but who don't" (quote from Neil deGrasse Tyson). I do not argue either with people who believe that the Earth is flat.*
This video may also help some of you to digest why 2 Voltmeters attached to the same 2 points in a circuit can give very different readings. th-cam.com/video/T6S5VS03xZc/w-d-xo.html
*Below follows Problem 7.50 in Griffith. Notice the drawing which he copied from Romer and he wrote: "Notice that V1 is not the same as V2, even though they are connected to the same points! See R.H. Romer, Am, J, Phys.50, 1089 (1982)"* drive.google.com/file/d/1G1a8_YNvB8X9xddUD27x9PE-j7Xbfo3m/view
@@lecturesbywalterlewin.they9259 Maybe this will help YOU: www. youtube. com/ watch?v= LGdN7rDB3XE
Off topic but dose anybody get the vibe that this older gentle man did ALOT of lsd back in the day 😂, not insulting his intelligence in anyway as he is sharp as a tack and easly out knowledge me any day. But he definitely has a "trippa" vibe about him
(9:11) In my opinion, people who 'religiously' believe in kirchoff's loop law, considers d(phi)/dt as potential (back emf) across the inductor hence include it in the closed loop integral for the circuit(which is of course incorrect) and so according to them kirchoff's loop law always holds. Thank you.
The problem is not that Kirchhoff's law is wrong. The problem is that you cannot remove a circuit from its environment. So assuming that the circuit is in a void, both of energy and matter, then it would hold true. So please don't say that it is not true, only say that it cannot be applied to every situation because of parasitic influences with the environment.
I never said that Kirchhoff's Loop rule is wrong. It's a special case of Faraday's Law. FL always works KVL only works if dphi/dt in FL is zero
Kirchhoff's loop rule (KVL) is older than Faraday's Law.
To now introduce a "modern version" of KVL which is really Faraday's Law is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html
I don't know how this could be made any more clear. I think what people don't understand in the induced EMF volt meter demonstration is that the meter and the wire leading to it is part of the coil. It's not really measuring between the two points it is connected to, it measures the part of the coil it is located at. By the way, I don't remember ever hearing of Kirchoff's loop rule before your video about it. Probably this was taught in school, but I don't remember hearing the name. I do remember hearing about Faraday's law.
when I was in highschool I learned that in a closed loop adding up all voltages lead to zero. We also never used the name Kirchhoff.
thanks for response sir I will watch your video :-)
Me a jee aspirant
Me : Visible confusion
I love you Mr. Lewin ... Your love from Iraq
Agree with you but there is a much more simple explanation why Kirchoff law does not apply. If you energize a circle of copper wire the energy disappear, but if you energize a capacitor, wich is practically the same, the energy stays
Seems i was wrong, my apologies
When given the option to analyze a circuit in terms of voltage or current, is current the more 'natural' choice then? It seems like current-based analysis holds in more situations than voltage-based analysis. Current must be conserved in a loop because of conservation of mass/charge (ie the 'stuff' in the loop) but ultimately voltage isn't? Is it because of voltage cannot be analyzed at a single point but current can?
I come from Electroboom but I must say thanks to the professor for taking time to respond and making videos in the name of physics.
:)
Wish more people were respectful of Dr. Lewin like you.
Im only a junior in EE and love Walter Lewin, I watch all his videos even if at some points they are over my head. My only gripe is I know Mr. Lewin really does not care to debate the topic but I would respectfully love it if he would on a personal basis talk with Mehdi from ElectroBOOM and show him where he is wrong. There is a productive reason behind this and that is if Mr. Lewin can show Mehdi where he is wrong (Mehdi will gladly accept he is wrong if he is) then Mhedi's new found understanding will translate to 1.9million others who may potentially ask the same question one day. Pass the information on a personal basis to those that can help pass it to the masses. I will always love your lectures but please understand that some people may learn more from a different platform style.
I do not debate whether the Earth is flat or not and I do not discuss whether Faraday's Law is correct or not. FL is classic 1st year college Physics and it is very basic. Viewers have access to all my lectures.
*ElectroBOOM's long video is dedicated to discredit my lectures. It is very insulting.* His 2 major attacks were related to KVL and my famous demo in Lect #16 of 8.02 in which I show that the 2 Voltmeters attached to the same 2 points in my circuit read very different values (as they should according to Faraday's Law) and that the polarities are reversed. He shows that he does not understand Faraday's Law. Kirchhoff's loop rule (KVL) is older than Faraday's Law. But he now introduces a "modern version" of KVL which is really Faraday's Law; this is a joke. Watch my video 5+3-8=0 th-cam.com/video/f3-SfzepuPs/w-d-xo.html. In my 2 latest videos ("To Agree or to NOT to Agree . . .) I set the record straight and I called a spade a spade; he has a masters degree in EE. His video is therefore an embarrassment.
One last thing and I will bow out. Please try to remember in this chaotic world of polotics, wars, lies and human suffering all of us here watching your lectures and those of us who watch his entertaining videos are here to learn. In school systems defined by govenment and financial systems some of us must undertake inadaquate teachings from lack luster professors and in todays world we rely heavily on outside sources. I have used your videos to understand "concrete" learnings that were skimmed over in my community college and people like Mehdi from ElectroBOOM serves to keep me entertained in a smart way when crunching the numbers gets overwhelming. This day and time youtube teaches us more than a class room and if those of you that have the followers play nice and work together you call affect millions of people in a positive way. Nothing but respect from a 38 year old low level student.
Limitations of Kirchhoff law is that it works only perfect for stable magnetic fields but not fluctuating field
the current conservation (1 of K's Laws) always applies. But that was not the issue here. None of K's laws are one of Maxwell's 4 eqs because you do not need them.
Dr. Lewin, this question is actually not arguing your explanation at all but maybe to better understand something "basic". Why do we say electricity moves from positive to negative "conventional theory"? Does it actually move from negative to positive "electron flow theory"? If you explain this in a lecture, could you please send me a link or refer me to that lecture? Thank you! Your work is amazing and your explanations are fantastic
Thank god we a teacher like you ms lewin , the other source want to teach us a wrong laws , the video is clear and absolutly we understund now (alhamdulilah) that kirshoff law doesnt work in all case . So clear why people doesn't understund
:)
Those are some really big pockets
Griffiths does not have it wrong of course!
Ofcoz not. Griffith, Purcell, Jackson could not possibly have it wrong!
I can't believe you really taught me E&M in college. Every day I'm amazed. Now I'm teaching college kids what you taught me 30 years ago.
THE RECTIFIER!
Good video.
22:08 - There are actually 3 (not 2) reasons why people have a religious belief in Kirchhoff.
And, the 3rd reason (goes to the heart of this debate, and) is because by applying Kirchhoff where it may not be suitable and in (questionable) ways that model the EMF as a voltage drop they can still get the correct answers.
This is like a dog chasing the wrong cat up the correct tree.
Essentially, people can “re-jig” the approach and/or circuit so that KVL (roughly) applies (for circumstances where delta EMF doesn’t = 0) and - even though that approach is fundamentally incorrect in terms of Faraday and Maxwell - they still arrive at the correct answer.
But in doing so (whilst it seems that approach validates the application of KVL in circumstances where delta EMF doesn’t = 0) they actually arrive at the correct answer in a manner that conceals how the path they took to get there was not entirely consistent with Faradays Law; and therefore questionable.
See my comments here for more detail.
th-cam.com/video/nGQbA2jwkWI/w-d-xo.html
Particularly point “I”.
Bottom line number 1; is that so long as you know you’re applying KVL in a manner that is fundamentally incorrect to such an extent that you're also aware of the limitations/constraints of that approach, even if you do arrive at the correct answer, then I guess it’s your choice.
However, the problem with that approach (aside from the fact that it is fundamentally misaligned with Faradays Law; which should be a cluster of red flags for anyone pursuing accuracy/precision) is that it can develop a false sense of security in what you analyse, test, and also claim; which could lead to bigger mistakes.
Bottom line number 2; is if your approach is derived from Faradays Law (as KVL is) but is not entirely consistent with Faradays Law, then Faradays Law applies.
Meaningfully considering this removes the issues associated with the fact that both parties (Electroboom and Professor Lewin) probably probed their circuits in ways that supported their intentions/results; although that in itself is not necessarily the main issue.
I am a student of standard 12th and our class ran into the same discussion, my teacher explain all the students in the same way as Dr.Lewin did. It was not at all hard to understand, I dont know why these *big brain* people in comments are getting mad about...
How I envy you! You really have a great physics teacher who looks into things.
I totally agree sir ... this explanation is outstanding!
:)
May I ask you where can I post solutions to your problems?As I already sent solution of problem 47 in one of your fb accounts ... but not sure whether its yours!
I am uploading it now. Internet is very very slow.
@@lecturesbywalterlewin.they9259 , its trying to obey KVL.
I think this video come after Electro boom video??? Any one ?? Tell me