Is MIT Prof. Lewin wrong about Kirchhoff's law?

[sarumonkee]

Theoretically, the part of induced emf on the wire cancels out the extra emf #1 and #2. Notice the direction. I'm on vacation and don't have access to the lab, so I'm still waiting for your experiment for verification

So in Lewin's setup, is he measuring the extra EMF across the resistors?

I won't be able to do more tests until probably this weekend.

 

[cabraham]

If you like, you can use distributed model of putting infinite voltage sources spread around the whole loop and draw out the circuit. Remember now, it is the EM books that use this distributed model to model the transmission line. They model as R per unit length, C per unit length etc. Then they make the length approach zero to derive the wave equation.

You draw the distribute model of the loop out, you can see immediately that you can just move all the distributed source to one side and become a lumped source. See my drawing.

I am not sure in the resistor loop, you will get the voltage ratio of the resistors. You can argue the Ohm's law don't work, but I argue that it could be because the voltage source ins laced inside the resistor that can throw the reading off. I am not sure in this case, but it would be interesting to see if Sarumonkee is willing to do the resistors loop experiment.

As I've stated many times, lumping the induced emf into a discrete source produces a correct result. But in order to do that you first have to know the value of said induced emf. If you have a loop to measure, & you find that the sum of voltages around said loop is non-zero, then you know that induction is taking place.

So you measure the sum around the loop, & that is the value you insert into the lumped source. But you first had to measure the distributed quantities in order to get the right values for the lumped equivalent circuit.

Once all parameters have been measured, one can continue using the distributed form, or one may lump the quantities into an equivalent circuit with no loss of accuracy. They both work.

My point is that many have stated that they would rather just use the lumped circuit & forget the distributed model. I only wish to point out that the distributed loop must first be measured before the lumped emf source value is known. So the distributed loop is needed in order to get the necessary data.

Is this debate still going? As far as I'm concerned this case is closed. Everyone agrees.

Claude

 

[hikaru1221]

So in Lewin's setup, is he measuring the extra EMF across the resistors?

He was measuring the net emf (= extra emf + induced emf), I believe. A theoretical proof of what I say:
Take the integral over the loop around resistor R1 and its corresponding voltmeter: $$\oint Edr = V_1 + IR_1 = 0$$ , according to FL (as there is no magnetic flux change through this loop). Here V1 is the "voltage" measured by the voltmeter. The microscopic Ohm's law implies that the total E-field (= E-field by charge + induced E-field), or the total emf, is the one that drives the current I through R1. Therefore, V1 corresponds to the total emf.

 

[stevenb]

@stevenb: MIT seems to be rewriting history, 5 minutes into http://ocw.mit.edu/courses/electric...tronics-spring-2007/video-lectures/lecture-2/, he gives the zero definition of KVL (admittedly this is what I learned too, I wasn't aware of the history of this till your earlier posts)!

Good point. I think Prof. Agarwal's treatment is excellent. First of all, he starts with the assumptions of no time changing flux outside any lumped element and no time changing net charge inside any element, which is necessary for the two Kirchoff laws he quotes. Then, when he sums voltage to zero, he says the word "voltage" rather than potential. This is OK because the term voltage is general enough to include EMF and potential. So Prof. Lewin's example does not meet the assumptions here. I wish the authors of all books would be as careful as this professor is in his lecture.

This is why I didn't try to make a big deal about the semantics of what KVL is. If you clearly define what you mean and the assumptions that are relevant, and then go on to apply the rule to the correct case, there is no problem.

I can definitely see the usefullness of this statement of KVL in cases where the assumptions are valid. We could get into battles over semantics here, but I really hate doing that. In some sense this is a third defintion of KVL. I can list them as follows.

1. The Classical/Maxwell Definition Generalized to any EMF source is the statement that the sum of EMFs equals the sum of potentials.

2. The Modern Lumped Element Definition is the statement that the sum of all voltages equals zero if there is no time changing flux outside a lumped element.

3. The Conservative Field Definition is the statement that potentials around a loop add to zero if there is no time changing flux outside or inside a lumped element.

At the risk of taking criticism, I could argue that the historical change was justified considering that most practical circuits of the earlier 20'th century met the lumped circuit assumptions. Perhaps, we are in need of another change back to definition 1 as modern cicuits using high frequency digital processing and magnetics-based switching power supplies are so prevalent. I've seen PCB layout people make the mistake of routing connections to A/D converter inputs (which measure voltage) around power magnetic sections, leading to measurement error. A good engineer should catch that mistake during review before it goes to production, but he won't if he thinks only in terms of definition 2 above, and forgets the starting assumption (or never learned that assumption). Keeping Faraday's Law in the back of the mind can save an engineer lots of grief.

 

[yungman]

Now we are all into back patting mode perhaps we should look seriously at yungman's transmission lines.

Some of these, extending perhaps across half a continent or more, are sufficiently long that the conditions at one part do not have time to affect a remote part if we take simultaneous 'readings' .

@cabraham

Thank you for noticing my comment about multiple mesh loops. This is not a problem if you take the original galvanic version of KVL for each loop.

@yungman
If you talk to the engineers at your works I expect they will be working in terms of admittances rather than resitances/impedances and using different mesh analysis methods anyway.

Oh and can anyone tell me why I now have a pink label?

When come to the case of the loop make up of all resistors material with no wire in between, I have to say I am not as sure. As you can see from my drawing in the last post, with micro generator laced in between the micro resistors, I just have a feeling that you are not going to get 9:1 measurement, but now that we have two distinct nodes, I am sure it still not path dependent. I believe you can still measure the same voltage both direction.

Anyway, I am really trying to not to check this thread as often, I had not have a good study section on my own materials for the last 3 days! I really better type less and work more! I try not to be here until at least tonight! But then again, my fingers might have the mind of their own!

 

[Studiot]

Yungman, you quoted my last post in its entirety, but did not make any reference or reply in your own text?

 

[yungman]

Yungman, you quoted my last post in its entirety, but did not make any reference or reply in your own text?

Sorry, I just continue from what you wrote, that I back paddle on the loop make up of all resistors materials with no wire, that I question whether we can get 9:1 voltage ratio because of the distributed sources. I still stand by the prosfessor's experiment with two resistor and a wire. That is a more clear cut case.

My guess ( only) is that the voltage is a super position of the transformer ( if you want to call Lorentz loop or what ever) and the two resistor. Meaning the voltage ratio might be 4:1 or 3:1 instead of 9:1. but it is still not path dependent. Sarumonkee said he might find time to do the resistor chain experiment soon. I just think you are not going to get 9:1 ratio on the 900ohm resistor in this case since the 15ohm take up most of the loop. Just a wild guess.

 

[Studiot]

But what has any of that to do with what I said?

Incidentally you do not need to play about soldering resistors. Just get some nichrome wire or lay down a shaped carbon track.

 

[sarumonkee]

But what has any of that to do with what I said?

Incidentally you do not need to play about soldering resistors. Just get some nichrome wire or lay down a shaped carbon track.

I'm open to donations :)

I thought about the carbon track, but I have no way of making it very regular. I was thinking of just writing with a graphite pencil on some transfer paper, but don't think that would come out very well.

 

[Studiot]

How about some auto highZ ignition leads?

 

[yungman]

How about some auto highZ ignition leads?

But that would be uniform resistance. YOu need to have something of two different resistance per unit length and combine together.

I think we might be onto something here, it would be very interesting to see the result. I bet if you marry half a turn of of 900 ohm total and half a turn of 100ohm total to form a loop, you would not get even close to 9:1 voltage ratio because if I am right about the micro sources, you will be measuring the resistor and the source instead of just the V=IR. Note that even if you don't get the V+IR relation, don't be too quick to say Ohm's law don't work under non conservative field etc. Because if you model the micro source in, KVL still work. Well talk is cheap, one experiment speak louder than anything else.

Maybe if you use one kind of resistor wire, half a turn make up of single wire and the other half turn make up of 9 wires in parallel, twist 9 wires together, use a meter to measure the length of the exact value of resistance you want (900ohm), then just cut the right length.

 

[yungman]

I'm open to donations :)

I thought about the carbon track, but I have no way of making it very regular. I was thinking of just writing with a graphite pencil on some transfer paper, but don't think that would come out very well.

Even if you build the loop with the discrete resistors like what I drawn, you should see reasonable results. If you make sure the wire junction between the two resistor is as short as possible(open twisted end is not part of the loop and don't matter like in my drawing), over 80% of the length of the loop will be of resistor material. You will see the effect if any. Don't sweat too much if you cannot find the resistent wires or carbon deposit. I have a suspicion that you are not going to get anywhere close to 0.9V on the 900 ohm resister if my theory of distributed source is correct, might not be even 0.5V. If you get close to 9:1 ratio, then I am blowing hot air. But in that case, still KVL holds and the voltage is not path dependent either.

We are looking forward to your result. Result speak louder than anything.

 

[yungman]

Guys, while we are waiting for the result, I have time just thinking about some theory that was thrown around in this case here:

Why are we talking about Lorentz force? My understanding about force only act on a charge that is moving. In this case, after the battery was removed, nothing is moving the electrons around the loop, only some thermal motion. Lorentz don't even apply here. It is very clear that

$$\vec F = q(\vec u X \vec B)\; \hbox { where } \;\vec u \;\hbox { is the velocity. }$$

And there is no force asseted on the charge if the charge is not moving. Recall magnetic field move the wire ONLY when there is a current passing through the wire? Also one more important point, the book very specificly said that the static magnetic field do not change the velocity of the particle, it only change the direction of the particle. So if the only motion of the electrons in the wire and resistors only change from random motion to random motion plus a few degree shift...still random, no current. Refer to P207 of Griffiths.


In my opinion, the formula in play in our case is :

$$V = \int _S (\nabla X \vec E) \;\cdot\; \hat n \; dS \;=\; \int _C \vec E \;\cdot\; \hat T \;dl \;=\; \int_S \frac{\partial \vec B}{\partial t} \;\cdot\; \hat n \;dS$$

From the experiment, the good professor use a changing magnetic field to induce the voltage into the loop. This is a time varying magnetic field and Lens law is in action in this case. And this is the voltage that drive the resistors. We'll have to see my distributed micro voltage inside resistors theory pan out or not.

 

[yungman]

Hey where is the enthusiasm?

 

[yungman]

Dr. Lewin is among the world's most qualified instructors regarding this material. I'm a little surprised at the EEs (or non-EEs) in the industrial community who are bashing Dr. Lewin. Those who do make me wonder how much e/m field theory they've had. Nothing personal, but will the critics of Dr. Lewin please state explicitly the errors in Dr. Lewin's teachings? He's a prof at MIT, an institution world renowed. Who are these critics anyway? What are their credentials? I'm just wondering.

One reason, first thing come to mind as I watch the first video is "How the hack he did the measurement"? How theoretical people that never held a probe will said you measure from the same two point and get two different reading. What? By hooking the scope probe from the left side or the right side to the same two points?

One of the difference between a physicist and engineer is the engineer has to produce something tangible, measuring at a real point, not an imaginary point like the professor did. I question the knowledge of electronics the professor has, and how many hours he spent on designing and building circuits. You understand this experiment is electronics?

In his experiment, I bet he connected the two resistor by wires, and that he missed the moon. I am waiting for Sarumonkee to come back with the result of the multiple resistors. But as I posted, I disagree that Lorentz force are in play in this case. It is FL that is in play.

Yes I notice the EM in EE is different from physics. We study a lot deeper into phasor, transmission line theory, smith charts etc. where physics (electro dynamics) get deeper into materials, potentials and more math. I follow the advanced EM courses of U of Santa Clara and pretty much finished what they taught. I did not attend any school, hack, I study mostly on my own in my whole career. I this is my third round studying EM, this time I study a lot of materials in “Intro to Electro Dynamics “ by Griffiths. There is a lot of stuffs that the EE books do not cover. BUT what we are arguing here is very basic laws like FL, KVL and conservatives. This are covered in the first 2 chapters. I still believe the professor did the experiment wrong. Nothing to do with the theory.

 

[cabraham]

Guys, while we are waiting for the result, I have time just thinking about some theory that was thrown around in this case here:

Why are we talking about Lorentz force? My understanding about force only act on a charge that is moving. In this case, after the battery was removed, nothing is moving the electrons around the loop, only some thermal motion. Lorentz don't even apply here. It is very clear that

$$\vec F = q(\vec u X \vec B)\; \hbox { where } \;\vec u \;\hbox { is the velocity. }$$And there is no force asseted on the charge if the charge is not moving. Recall magnetic field move the wire ONLY when there is a current passing through the wire? Also one more important point, the book very specificly said that the static magnetic field do not change the velocity of the particle, it only change the direction of the particle. So if the only motion of the electrons in the wire and resistors only change from random motion to random motion plus a few degree shift...still random, no current. Refer to P207 of Griffiths.


In my opinion, the formula in play in our case is :

$$V = \int _S (\nabla X \vec E) \;\cdot\; \hat n \; dS \;=\; \int _C \vec E \;\cdot\; \hat T \;dl \;=\; \int_S \frac{\partial \vec B}{\partial t} \;\cdot\; \hat n \;dS$$

From the experiment, the good professor use a changing magnetic field to induce the voltage into the loop. This is a time varying magnetic field and Lens law is in action in this case. And this is the voltage that drive the resistors. We'll have to see my distributed micro voltage inside resistors theory pan out or not.

The Lorentz eqn has 2 terms, 1 for electric, & 1 for magnetic. I've already stated said eqn as F = q(E + u X B).

Regarding the mag field influence on a charge, it can indeed change its direction, but not its speed or kinetic energy. By changing its direction, its "velocity" is also changing, as velocity is a vector quantity consisting of speed & direction.

I use momentum & kinetic energy when describing Lorentz force. An E field can change both, but a B field can only change momentum, not KE.

Did I help, or make matters worse?

Claude

 

[atyy]

Lewin is not a theorist.

 

[yungman]

The Lorentz eqn has 2 terms, 1 for electric, & 1 for magnetic. I've already stated said eqn as F = q(E + u X B).

Regarding the mag field influence on a charge, it can indeed change its direction, but not its speed or kinetic energy. By changing its direction, its "velocity" is also changing, as velocity is a vector quantity consisting of speed & direction.

I use momentum & kinetic energy when describing Lorentz force. An E field can change both, but a B field can only change momentum, not KE.

Did I help, or make matters worse?

Claude

No, since the only motion of electrons in the circuits with no current is random motion, changing the direction of a random motion is still random motion. You cannot make the random motion to become the direction of the wire to travel down the wire as current.

It is very obvious that FL is in play like what I wrote. The resistor body is still part of the loops. As I said before, if the professor use a 6" wire to connect the two resistor, most of the induced emf is on the wires. In case of the loop making up of resistors material, the result is the same where the micro voltage sources are embedded inside the resistors. Still waiting for the experiment result that if what I postulated is true, we are not going to see 9:1 voltage ratio on those resistors, not even close.

 

[yungman]

Lewin is not a theorist.

I can asure you he is not hands on!

 

[yungman]

The Lorentz eqn has 2 terms, 1 for electric, & 1 for magnetic. I've already stated said eqn as F = q(E + u X B).

Regarding the mag field influence on a charge, it can indeed change its direction, but not its speed or kinetic energy. By changing its direction, its "velocity" is also changing, as velocity is a vector quantity consisting of speed & direction.
BUt as I said, if there is no current in the loop, electrons are moving randomly. So applying a mag field just change the direction of the random movement and still is random. Not current around the loop created.
I use momentum & kinetic energy when describing Lorentz force. An E field can change both, but a B field can only change momentum, not KE.
Even if you argue it is a pulse and it is EM that consist of E field. If you put the loop on xy plane and the mag field is in z direction, the E field is propagating in z direction also because even though it is quadriture to the mag field, the direction of propatation still perpendicular to the loop. The loop being perpendicular to z direction will not be affected by E field in z direction. Remember induced E field is alway opposite to the external E field.
Did I help, or make matters worse?

Claude

I don't think the Lorentz law apply. THe only law in play is FL which is the induced voltage.

 

[yungman]

I was going to put in my comment on the professor's video. It was closed, or else I'll give him a piece of my mind.

 

[cabraham]

I don't think the Lorentz law apply. THe only law in play is FL which is the induced voltage.

Lorentz' law does apply. How can it not apply? If loop is immersed in a time varying mag field, it is also subjected to a time varying elec field. E & B are normal in space. The free electrons in the loop are acted upon by the E force. Once in motion the B force is incurred normal to the E force. Otherwise, how can the electrons ever start moving? In order to accelerate an electron you need an E field. Whenever a time varying B is present, so is E present. Under time changing (dynamic) conditions, neither one can exist independently. The E force can change not only the electron's direction, but its speed & KE as well. The B field can only change the electron's direction, & only if the electron is already moving.

Once the E field accelerates the electron, it is not random motion, but drift along the direction of the E field. The mag field B, acts upon the electron normal to its velocity. So, Lorentz law applies here. Otherwise, how would the electrons ever start moving? I can't believe that you don't see Lorentz' law as in effect here. Please elaborate. What gets the electrons initially moving if not Lorentz force? Just asking.

Claude

 

[yungman]

Lorentz' law does apply. How can it not apply? If loop is immersed in a time varying mag field, it is also subjected to a time varying elec field. E & B are normal in space. The free electrons in the loop are acted upon by the E force. Once in motion the B force is incurred normal to the E force.

Read the FL, E induced in the loop caused by B is not the same as the E that accompany the B. THis induced E is not the same as in the Lorentz equation. You have to be very careful about this. Vary B alway have E accompany along and is quad to the B, but this is perpendicular to the induced E in the loop. Only the B portion act on the loop.

Otherwise, how can the electrons ever start moving? In order to accelerate an electron you need an E field. Whenever a time varying B is present, so is E present. Under time changing (dynamic) conditions, neither one can exist independently. The E force can change not only the electron's direction, but its speed & KE as well. The B field can only change the electron's direction, & only if the electron is already moving.

Once the E field accelerates the electron, it is not random motion, but drift along the direction of the E field. The mag field B, acts upon the electron normal to its velocity. So, Lorentz law applies here. Otherwise, how would the electrons ever start moving? I can't believe that you don't see Lorentz' law as in effect here. Please elaborate. What gets the electrons initially moving if not Lorentz force? Just asking.

Claude

If you think of the loop is on the xy plane center at origin, the external EM field in +z direction, the EM is perpendicular the the loop. The E in the EM that propagate in +z direction is perpendicular to the loop and has NO effect on whatever E in the loop.

Remember induced E by an external E is always opposite in direction only. That is the reason we have the FL that stated only the B is in action to cause the induced E. There are two E here, you have to be careful not fixing them up.

 

[cabraham]

If you think of the loop is on the xy plane center at origin, the external EM field in +z direction, the EM is perpendicular the the loop. The E in the EM that propagate in +z direction is perpendicular to the loop and has NO effect on whatever E in the loop.

Remember induced E by an external E is always opposite in direction only. That is the reason we have the FL that stated only the B is in action to cause the induced E. There are two E here, you have to be careful not fixing them up.

Maxwell says otherwise. If the B is normal to the loop (x-y plane), then the E is in the x-y plane. You've placed both B & E on the z axis, which opposes Maxwell.

Either form of ME applies, integral or differential. For the diff form (or "at a point" form):

curl E = -dB/dt.

If B is non-zero & time varying, then curl E is non-zero as well. For that to happen, E is non-zero, since the curl of a zero vector is zero. This E field exerts a force on a free charge resulting in motion of said charge. In order for charge to circulate in x-y plane, E must have a component in x-y plane. Using your established reference with B along z axis, the curl of E is along the z axis only for E in the x-y plane.

Hence, E produces a force upon free electrons in the loop. Once they are in motion, they are subjected to the force due to B as well in addition to E.

Have I overlooked anything?

Claude

 

[yungman]

Maxwell says otherwise. If the B is normal to the loop (x-y plane), then the E is in the x-y plane. You've placed both B & E on the z axis, which opposes Maxwell.

Either form of ME applies, integral or differential. For the diff form (or "at a point" form):

curl E = -dB/dt.

If B is non-zero & time varying, then curl E is non-zero as well. For that to happen, E is non-zero, since the curl of a zero vector is zero. This E field exerts a force on a free charge resulting in motion of said charge. In order for charge to circulate in x-y plane, E must have a component in x-y plane. Using your established reference with B along z axis, the curl of E is along the z axis only for E in the x-y plane.

Hence, E produces a force upon free electrons in the loop. Once they are in motion, they are subjected to the force due to B as well in addition to E.

Have I overlooked anything?

Claude

You keep talking about the induced E in the loop. The external EM in +z direction has the component of E that is in +z direction and has no effect on the loop. You kept talking about varying B has E, this external E is not the induced E and is in +z direction.

The induced E in the loop is purely caused by the external B only. We are talking about two different E fields here.

Yes, the induced E in the loop cause the electrons to run, but that is because of the external B, and this the very essence of FL, not Lorentz.

 

[yungman]

To avoid confusion, I upload a drawing which show Lorentz force:

$$\vec F = q ( \hat z E_{(x)} +\vec u X \hat z H_{(y)})$$

Where the $\hat z E_(x) \;&\; \hat z H_{(y)}$ are the electromagnetic wave.

The induced E is $$\; \vec E_{EXT} \;=\; \hat {\phi} E_{(r)} \;$$ as shown.

As you can see, $\hat z E_(x)$ is normal to the loop and has no effect.

It would be opposit if instead of the loop, we have a straight wire in z direction. In this case, the E assert force on the electrons inside the wire, but here, the B has no effect because B is parallel to the wire.

 

[cabraham]

To avoid confusion, I upload a drawing which show Lorentz force:

$$\vec F = q ( \hat z E_{(x)} +\vec u X \hat z H_{(y)})$$

Where the $\hat z E_(x) \;&\; \hat z H_{(y)}$ are the electromagnetic wave.

The induced E is $$\; \vec E_{EXT} \;=\; \hat {\phi} E_{(r)} \;$$ as shown.

As you can see, $\hat z E_(x)$ is normal to the loop and has no effect.

It would be opposit if instead of the loop, we have a straight wire in z direction. In this case, the E assert force on the electrons inside the wire, but here, the B has no effect because B is parallel to the wire.

In an e/m wave, E & H (B) are normal. I'll double check tonight, but I'm perplexed by your inference that the external B & E fileds are both along the z axis. For a transverse e/m wave, E & H/B are perpendicular to each other, not coincident. I'll get back later.

Claude

 

[yungman]

In an e/m wave, E & H (B) are normal. I'll double check tonight, but I'm perplexed by your inference that the external B & E fileds are both along the z axis. For a transverse e/m wave, E & H/B are perpendicular to each other, not coincident. I'll get back later.

Claude

EM always goes in pair and field has to propergate along the z- axis in his experiment. Yes the E and in the EM wave are normal to each other, they just propagate in z direction.

Also you can look at it this way, $\hat z E_{x}$ is occilating along x direction and it affect the loop both directions and the result cancel out and will not push electron either direction. Only the magnetic field moving the electrons by inducing the electric field along the loop. as shown in arrow on the loop.

I am no expert in EM, this is my understanding. I would not dare to challenge the professor's knowledge on EM, I challenge him on his set up where he drawn the conclusion.

 

[yungman]

In an e/m wave, E & H (B) are normal. I'll double check tonight, but I'm perplexed by your inference that the external B & E fileds are both along the z axis. For a transverse e/m wave, E & H/B are perpendicular to each other, not coincident. I'll get back later.

Claude

You have a chance to look into this? I am no expert in EM, that is my understanding and I am willing to be wrong and learn.

 

[cabraham]

Yes I did look. For a transmission line (2 wire, parallel or coax), the wave propagates in TEM (transverse electromagnetic) mode. So does a space wave. But for a waveguide, TE (transverse electric) & TM (transverse magnetic) modes exist, no TEM mode at all takes place.

For TEM mode, if wave propagation is along z axis, then E is in x axis, & H is in y axis, or any orientation in x-y plane normal to each other. For TE mode, propagation remains along z axis, E is in x axis, but H is in y-axis & z axis. E is transverse (normal) to prop, but H has 2 components, 1 normal to prop, & 1 coincident with prop. So if wave prop is in z axis, E is in x axis, H is in y & z axes. Only E is transverse to prop direction.

For a TM it's vice versa. So in Prof. Lewin's setup, only the TEM mode takes place. If energy is propagating in z direction, then E & H/B are normal to each other in x-y plane, as well as normal to prop.

"Inducing" an E field into the loop is a colloquial phrase. This E field is present in space regardless of whether or not the loop is there. H & E cannot exist independently under time changing conditions. Sorry to be late responding. Christmas season, shopping, fixing up the house, you know.

Claude

 

[yungman]

Yes I did look. For a transmission line (2 wire, parallel or coax), the wave propagates in TEM (transverse electromagnetic) mode. So does a space wave. But for a waveguide, TE (transverse electric) & TM (transverse magnetic) modes exist, no TEM mode at all takes place.

For TEM mode, if wave propagation is along z axis, then E is in x axis, & H is in y axis, or any orientation in x-y plane normal to each other. For TE mode, propagation remains along z axis, E is in x axis, but H is in y-axis & z axis. E is transverse (normal) to prop, but H has 2 components, 1 normal to prop, & 1 coincident with prop. So if wave prop is in z axis, E is in x axis, H is in y & z axes. Only E is transverse to prop direction.
In the professor's case, it is a TEM because he generate a time varying magnetic field which automatically have E field accompany along from z direction. That is the reason I drew both E and H along the z direction. Your accessment is the same as my drawing, E in x and H in y( which I call E(x) and H(y) in my drawing. but they propergate at z direction. This is just a case of simple transverse electromagnetic wave (TEM) propagate in z direction.
For a TM it's vice versa. So in Prof. Lewin's setup, only the TEM mode takes place. If energy is propagating in z direction, then E & H/B are normal to each other in x-y plane, as well as normal to prop.z direction. In real life, the wave is usually polarized, either circular etc. It is not exactly straight E in x and H in y. But the result is the same as long as it propagate in z direction. So we just keep the discussion as E in x and H in y.

If you look at this way where E varying in x direction through the loop that is on xy plane, the effect cancel out because it affect in +ve x just as much as -ve x direction and the result is no effect on the loop due to the E field propagate up. Still only the H field only in play, which is Faraday's Law only, not Lorentz force.

"Inducing" an E field into the loop is a colloquial phrase. This E field is present in space regardless of whether or not the loop is there. H & E cannot exist independently under time changing conditions. Sorry to be late responding. Christmas season, shopping, fixing up the house, you know.
Yes, the source( external ) E and H cannot exist independently under time varying condition. My point is the E is normal to the resistor loop and has no effect. Therefore I claim only the H is in play and is 100% Faradays law, not Lorentz force.

Claude

That is what I have been driving at all this time that this is nothing more than magnetic induction into a closed loop consist of two resistors. Nothing more and the professor make a big sting out of nothing. AND he is wrong. I am not saying his conservative or non conservative ...well, don't know how other way to put it...BS... is wrong, it is just not in play in his experiment. I still say, it is so obvious that any praticing engineer can spot this mistake he made. I tried to put my comment in and want to challenge him out to join in, but problem is the comment section in youtube is closed. And yes I will confront him if possible. I deal with too many PhDs in my career. They are only human and they make mistake just as anyone else. Only difference, this guy is so arrogant about it. The nerve of him to make a video on youtube. He should at least be humble enough to summit a paper in AIP and let others to have a peer review first, then publish it in AIP instead of making a scene on youtube where 99.99% of the public have no idea what he is talking about and think he actually have something valid.

I wonder whether Sarumonkee have done the new experiment yet!

 

[Studiot]

I don't see the point of this protracted discussion about FL v Lorenz, or the castigating others for their point of view.

I pointed out, way back, that correct application of Kirchoff leads to a simple and unambiguous resolution of the issue.

All Proff Lewin did wrong was to offer an inappropriate version of Kirchoff.
There are many instances in mathematical physics where we can loose something if we equate to zero.

 

[yungman]

I don't see the point of this protracted discussion about FL v Lorenz, or the castigating others for their point of view.

I pointed out, way back, that correct application of Kirchoff leads to a simple and unambiguous resolution of the issue.

All Proff Lewin did wrong was to offer an inappropriate version of Kirchoff.
There are many instances in mathematical physics where we can loose something if we equate to zero.

Not castigating others, just one, the professor because of his arrogance. I think we have a good discussion here and I think we are all very civilize with each other. I think it is very important to establish that FL is in play here to make sure there is a voltage generator or distribute voltage generators in the loop, then everything make sense and KVL apply perfectly in this case...not in all cases, just this one.

 

[hikaru1221]

@yungman: Why does the wave propagate in the z-direction?

 

[Studiot]

not in all cases,

Would you like to provide an example?