Does Kirchhoff's Law Hold? Disagreeing with a Master

[Sredni]

To make things easier i will summarize most of my claims in a list:
1)
...
19)

I might have missed a few but these are the ones i remember right now. Any disagreement on these?

If you were a computer, I'd reboot you. 
(I've edited one of the posts in the previous page with the origin of the scalar and vector potentials, just in case it could help in sorting some of the points out)

[Berni]

I might have missed a few but these are the ones i remember right now. Any disagreement on these?

I would add definition of voltage to 2 ). Version "True voltage is integral of all forces acting on a electrons along the path" is kinda tricky because some may think that electron(s) shall be carried all the way along the path for voltage to appear, which is untrue. IMHO worth to mention more straightforward "the work needed per unit of charge to move a test charge between the two points". It also "connects" better to volt = joule/coulomb equation.

I disagree with 8 ) because both "all forces on electrons along the path" and "work per unit of charge" voltage definition variants allows voltage to be present on terminals of zero resistance "open lengths of wire" or inductor. After all there's well-known equation: V = L(di/dt)

Kinda offtopic or maybe not. -How special relativity is related to this discussion:

p.s. How to (easily) avoid this gigantic thumbnail appearing when I include URL to YT video?

Yeah good point 2) should have a definition of voltage included to make sure another definition doesn't get assumed. The wording "integral of all forces on electrons" doesn't assume a single electron but rather the average contribution from all of them, but yeah the wording of "work per unit charge needed to move along the path" is actually a bit more accurate and unambiguous.

For 8 ) Yes V = L(di/dt) is sort of a "patch" to make voltage appear on the terminals of transformers when using the textbook definition of voltage. It assumes a lumped inductor and places this voltage across its terminals even tho the voltage inside the inductor is ether zero, the resistive loss, or undefined. So by moving a nanometer into the transformer terminals you get the 0V solution but the moment you step on the edge of a transformer terminal this "patch formula" comes into effect and suddenly you have lots of voltage.
https://en.wikipedia.org/wiki/Voltage#Definition (see bottom of section "Definition as potential of electric field")
If you keep reading you get to the alternative definition of voltage that i call "effective voltage" or "charge density voltage". This definition does not require the patch formula from before to make voltage appear on transformer secondaries. There simply is a voltage all throughout the length of the transformers winding as well as on the terminals with no sharp transition anywhere. (Tho this L(di/dt) formula is still incredibly useful for modeling inductors in circuit analysis). This is a much more elegant solution in my opinion (And as a bonus is never undefined or path dependent).


Oh and yes that is an excellent video for explaining how and why magnetism works in a very intuitive way. Every electronics engineer should watch it at some point. (And no i don't think you can prevent embedding of youtube links)

...you keep saying wires always have no voltage across them (apart from restive drop). So you are now saying that wires can have voltage across them?

You can have voltage at the terminals, with zero field and zero voltage inside the secondary. (EDIT: of course in case sigma = infinity, so what I called copper has to be thought as a perfect conductor - otherwise, we would see minimal resistive losses and a negligible E complying with j = sigma E).
These are just the essential pictures of a long story that starts with electrostatics, so consider this a sneak preview (and please do not mind too much at signs, they were not my priority here)

Consider a single loop secondary and a closed IMAGINARY, MATHEMATICAL closed path going through the copper and joining the terminals. Like this



How does a transformer work? By applying Faraday. Not Kirchhoff, Faraday. I have a closed path, it defines an area. Let's do it!

Yes you are going to have lots of trouble calculating this with Kirchhoffs circuit laws, those laws don't care about inductors of any form. Its like trying to undo a bolt with a screwdriver, its simply not meant for doing that. All that Kirchhoffs cirucit laws are used for is defining the behavior of voltage and current in cirucits. Its the job of circuit modeling to plug the correct voltage equation into KVL when dealing with inductors to tell it what the voltage on a inductor is. (See my claim 15)

Ok, nice formula, how do I fit it into my circuit?
Let's decompose the closed path into two partial open paths and see what we can get out of that:



We've got this:



and the notion that you can have zero field and zero voltage inside the wire of the secondary coil, while having voltage at the terminals. Try to explain this with KVL.

Yet if you use the conservative definition of voltages KVL suddenly works across all of this circuit without having to define a sharp point where the coil of wire stops being an inductor and becomes a normal wire where in a infinitesimally small area the voltage suddenly shoots from 0V to whatever voltage Faradays law says it should have. What if i move that transition point somewhere else?

[ogden]

For 8 ) Yes V = L(di/dt) is sort of a "patch" to make voltage appear on the terminals of transformers when using the textbook definition of voltage. It assumes a lumped inductor and places this voltage across its terminals even tho the voltage inside the inductor is ether zero, the resistive loss, or undefined. So by moving a nanometer into the transformer terminals you get the 0V solution but the moment you step on the edge of a transformer terminal this "patch formula" comes into effect and suddenly you have lots of voltage.

Let's put aside L(di/dt) which is not "patch" at all, but pay attention to what happens with electrons, thus charge in the coil during flux change. Charge is pushed to the one end of the coil. I can't see how resulting voltage on the terminals could be zero.

[Berni]

For 8 ) Yes V = L(di/dt) is sort of a "patch" to make voltage appear on the terminals of transformers when using the textbook definition of voltage. It assumes a lumped inductor and places this voltage across its terminals even tho the voltage inside the inductor is ether zero, the resistive loss, or undefined. So by moving a nanometer into the transformer terminals you get the 0V solution but the moment you step on the edge of a transformer terminal this "patch formula" comes into effect and suddenly you have lots of voltage.

Let's put aside L(di/dt) which is not "patch" at all, but pay attention to what happens with electrons, thus charge in the coil during flux change. Charge is pushed to the one end of the coil. I can't see how resulting voltage on the terminals could be zero.

Yes i also don't like how that works but that's how the formal textbook definition of voltage makes it work.

When you have a wire in a changing magnetic field that field can induce the non conservative E field along it. Because the electrons in a wire are free to move they start marching in the direction that field is pushing them. As a result they end up bunched up at one end of the wire. But when electrons are bunched up like that they create there own E field. This field opposes the magnetically induced E field and the electrons keep marching along until they are creating an electrostatic E field that exactly opposes the magnetically induced one. Now all the fields around the electrons sum up to zero so they stay still in there cozy equilibrium point.

So now if you take the formal definition of voltage (Work needed to move a unit of charge along a path) you will find that zero force is needed to move an electron along the wire because they is no force acting against you. As such by the formal definition of voltage there is 0V along the wire. If you connect a load to the terminals of this coil then the voltage becomes undefined because you get a different result if you travel between the terminals along the path going trough the coil and a different result if you traverse the path by going trough the load. This is the whole reason why Dr. Lewin is not wrong by saying there are two voltages across the points in his circuit and the root cause for what we are arguing about in this thread.

The alternative is to instead use the "effective voltage" definition that is basically just the difference in charge density at each point. This simply ignores the troublesome noncoservative E field along the wire and instead just sees the effect of it in the form of charge separation. If you look at the coil of wire again using this definition now you find that as you travel along the wire you find electrons bunched up together more and more and as such the voltage smoothly increases along the coil until reaching its maximum value at the terminals. Connecting a voltmeter to the terminals measures this exact voltage, or connecting a load to the terminals pushes a current trough it according to Ohms law, path does not matter anymore and we always have exactly one solution for the voltage across the coils terminals.

This is why i think the "effective voltage" definition makes more sense and is more useful for calculations. Under this definition KVL works just fine too.

The problem is that the first definition is considered to be the formal definition of voltage and as such i can't argue against using it. I can't just ignorantly say "That's not what voltage is" just because its not something i would want voltage to be defined as. So we have to just deal with having two definitions of voltage, one of them causes the paradox in Dr. Lewins experiment, the other does not. I fully support both definitions of it, but my personal honest opinion is that the "effective voltage" definition is more useful.

[ogden]

When you have a wire in a changing magnetic field that field can induce the non conservative E field along it. Because the electrons in a wire are free to move they start marching in the direction that field is pushing them. As a result they end up bunched up at one end of the wire. But when electrons are bunched up like that they create there own E field. This field opposes the magnetically induced E field and the electrons keep marching along until they are creating an electrostatic E field that exactly opposes the magnetically induced one. Now all the fields around the electrons sum up to zero so they stay still in there cozy equilibrium point.

More electrons bunched at the one end than another equals potential difference. That "cozy equillibrium point" happens when capacitor connected to wire loop is finished charging. You may want to say "there's no capacitor" - read my comments below.

So now if you take the formal definition of voltage (Work needed to move a unit of charge along a path) you will find that zero force is needed to move an electron along the wire because they is no force acting against you. As such by the formal definition of voltage there is 0V along the wire.

Moving electrons to one end of the wire will create opposing magnetic field, opposing force. This means that to move electron, nonzero work shall be done. So there's your definition of voltage that predicts voltage.

If you connect a load to the terminals of this coil then the voltage becomes undefined because you get a different result if you travel between the terminals along the path going trough the coil and a different result if you traverse the path by going trough the load.

As wire loop can't be infinitely small (area enclosed by the loop shall be > 0), it will be some kind of capacitor as well - you like it or not. So there's your load - capacitor that becomes charged. When magnetic field does not change anymore, this "parasitic capacitor" immediately discharges through low resistance of the wire.

[Sredni]

 







(my turn)

[Berni]

More electrons bunched at the one end than another equals potential difference. That "cozy equillibrium point" happens when capacitor connected to wire loop is finished charging. You may want to say "there's no capacitor" - read my comments below.

Yes there is indeed capacitance there. This is why i claim a open length of wire can act as a LC circuit (As said in my claim no. 7)

My point is that since the magnetic EMF is distributed along the wire you also get a smooth gradient of charge density along the wire. Its not like the charge density along the wire is constant but then at the very end of the wire there are lots of bunched up electrons while on the other end there are missing electrons.

The textbook definition of voltage makes it seam like you only have excess electrons at the very end while they are perfectly evenly distributed between the ends. But this is not the case.

Moving electrons to one end of the wire will create opposing magnetic field, opposing force. This means that to move electron, nonzero work shall be done. So there's your definition of voltage that predicts voltage.

Yes moving an electron does create a magnetic field around it, but the sea of free electrons inside the wire gets pushed around in a way that creates an exactly opposing electrostatic E field. This is where the idea comes from that it is impossible to have a E field inside a superconductor. Any magnetically induced E field gets  canceled out by electrons rearranging to create a opposing electrostatic E field. Force exerted on electrons comes from the sum of all E fields and with the field being zero the force is also zero. Alternativly you could also explain it as the electrostatic E field acting on it while a magnetic field acts on it in the opposing direction. You can't have the induced E field and the magnetic field simultaneously acting on the electron. This induced E field is simply the interpretation of the magnetic fields effect on charges (due to Einsteins special relativity). This induced field is not a real E field, its sort of a virtual E field caused by the interaction of charges with magnetic fields. So you ether imagine the effect as moving charges experiencing force when moving trough a magnetic field, or as an a moving magnetic field creating this virtual E field trough the effects of special relativity and this E field then produces force on electrons.

Lets just let Sredini, bsfeechannel,rfeecs... etc explain and advocate for this kind of voltage definition. I honestly don't like this definition myself (its messy and confusing) so i rather not explain it more than necessary. I just wanted to say that when these forum members are talking about there being no voltage in a wire when in a changing magnetic field, they are actually correct if you use the formal textbook definition of voltage.


I'm not going to say they are wrong just because i don't agree with this being a good definition of voltage. It is a widely accepted definition written down in countless literature. I was just commenting on why i think this is not a very good definition of voltage and why the "effective voltage" makes more sense to me. I prefer the "effective voltage" definition due to making more sense, but im not going to say the other definition is wrong just because i don't like it.

Even if i don't agree with some other stuff they claim, im not going to say its wrong just because i don't like it. But i will certainly argue about things that i think are genuinely wrong according to other facts.

As wire loop can't be infinitely small (area enclosed by the loop shall be > 0), it will be some kind of capacitor as well - you like it or not. So there's your load - capacitor that becomes charged. When magnetic field does not change anymore, this "parasitic capacitor" immediately discharges through low resistance of the wire.

Yes i fully agree.

[Sredni]

I might have missed a few but these are the ones i remember right now. Any disagreement on these?

I would add definition of voltage to 2 ). Version "True voltage is integral of all forces acting on a electrons along the path" is kinda tricky because some may think that electron(s) shall be carried all the way along the path for voltage to appear, which is untrue. IMHO worth to mention more straightforward "the work needed per unit of charge to move a test charge between the two points". It also "connects" better to volt = joule/coulomb equation.

This post has been shortened and cleansed to avoid upsetting other children.
Whatever was written here can be found in one or more of the following books (in no particular order, and without mentioning the usual suspects Feynman, Purcell, Griffiths, Ohanian, Jackson):


Kip
Fundamentals of Electricity and Magnetism 2nd ed

Lorrain, Courson
Electromagnetic Fields and Waves 2nd ed

John Kraus
Electromagnetism 2nd to 4th ed

Ramo, Whinnery, VanDuzer
Fields and Waves in Communication Electronics 2nd or 3rd ed

Panofsky, Phillips
Classical Electricity and Magnetism 2nd ed

Bleaney
Electricity and Magnetism 3rd ed

Nayfeh, Brussel
Electricity and Magnetism

[ogden]

What do you see?
Or, better yet: what do you NOT see?

There are no voltmeters.
There are no probes.

There is no spoon.

And yet, the voltage between A and B can have two different values.

If you are right - then why there is voltage on transformer terminals? There's same voltage - you measure with 10MOhm voltmeter alone or with 1K resistor in parallel. Please explain why "Romer's loop" wire have 0V on it's ends but any other transformer nonzero voltage? It's question to explain transformer, not to profile me from psychological or educational point.

[Sredni]

If you are right - then why there is voltage on transformer terminals?

I... I... I thought I just explained that.
Ok, let me answer with a question.

EDIT: On second thought, no.

This post has been shortened and cleansed to avoid upsetting other children.
Whatever was written here can be found in one or more of the following books (in no particular order, and without mentioning the usual suspects Feynman, Purcell, Griffiths, Ohanian, Jackson):

Panofsky, Phillips
Classical Electricity and Magnetism 2nd ed

John Kraus
Electromagnetism 2nd to 4th ed

Ramo, Whinnery, VanDuzer
Fields and Waves in Communication Electronics 2nd or 3rd ed

Bleaney
Electricity and Magnetism 3rd ed

Nayfeh, Brussel
Electricity and Magnetism

Kip
Fundamentals of Electricity and Magnetism 2nd ed

Lorrain, Courson
Electromagnetic Fields and Waves 2nd ed

"Books" are static paper based documents that can be found in libraries. They are like smartphones, but (usually) bigger, with lots and lots of extremely thin flexible e-ink screens and a very long battery life. Libraries are...
Oh, never mind. Keep on pushing that square peg into that round hole. With a big enough hammer, it will fit.

[Berni]

I do have to agree with Sredini on his post( https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2096638/#msg2096638 ). This is indeed how voltage works when its used as is formally defined with "The work needed to move a unit of charge along a path"

The reason that the voltmeter is reading a voltage is that its essentially a amp meter with a 10MOhm resistor inside, because this resistor is only a tiny part of the whole loop (or is not even inside the magnetic field) means it is not being affected by the the non conservative E field induced by the magnetic field, but is seeing all of the electrostatic E field caused by charge separation at the transformers terminals. So if we integrate the E field across this 10M resistor we are basically only seeing the conservative electrostatic E field. This causes a current to flow trough it according to Ohms law and the voltmeter displays the voltage needed to push that current.

Its not wrong, its just a more complicated roundabout way of getting to the answer.

Alternatively you could simply use the "effective voltage" definition that only looks at the charge density and ignores the non conservative field all together. Then you always have voltage on the transformer terminals no matter what you do (apart from turning the transformer off). This voltage is spread over all the turns of the coil in the transformer and if desired you can tap into it at any point to give you any voltage in between. No need to coax this voltage into existence by connecting a load to the transformer. Its simply there all the time and you can poke your voltmeter at it to see it.

This is why i prefer the "effective voltage" flavor of voltage much like ogden does, it just simply makes more sense.

[bsfeechannel]

Some academic scientists and their worshippers may say "Look! I discovered that voltage is path-dependent" while actual "discovery" is just electromagnetic induction."

Bad probing is the lame excuse that people not comfortable with electromagnetism give when academic scientists set up an experiment to explain exactly WHY voltage is path dependent under a varying magnetic field.

A probing technique that suppresses the very effect you are trying to demonstrate is called facepalm probing.

[ogden]

If you are right - then why there is voltage on transformer terminals?

The field outside will not be zero, though.

Thank you. 

[jesuscf]

And yet, the voltage between A and B can have two different values.

At the same exact time?  Maybe you have to take into account the magnetic field generated by the flowing current through the wire...

[bsfeechannel]

I have to agree with Ogden. Who are you actually arguing with?

Read below.

To make things easier i will summarize most of my claims in a list:

Thank you.

1) There are indeed two voltages present at the measured points in Dr. Lewins experiment when using the formal textbook definition of voltage.

[snip]

9) Lengths of wire connecting the voltmeter to the probing points are part of the circuit and need to be analyzed along with the rest of the circuit. These wires transfer the voltage from the probing points to the voltmeter terminals where it is actually measured. If it is found that these wires generate a voltage that affects the voltmeters reading then this voltage must be subtracted out to get the voltage at the probe points. Failure to realize this, correct it, or compensate for it is considered as "bad probing".
10) Changing the path of the probe wires in Dr. Lewins circuit does change the voltmeter reading due to changing the charge density present on the voltmeter terminals. However when doing correct probing as mentioned above the result of the voltage at the probing points it always the same, regardless of wire path or voltmeter location (The effect is always substracted out).

The "correct probing" is a technique to avoid UNWANTED induction. But Lewin's experiment is exactly to show how voltage is dependent on the path under induction. So the voltage induced by the probes is PART of the experiment. You cannot subtract it out!

If you set up an experiment and employ a probing technique to suppress the very effect you are trying to demonstrate, you are on dope.

11) Kirchhoffs circuit laws always work in circuit mesh models where all voltages use the "effective voltage" definition
12) Kirchhoffs cirucit laws can not be directly applied to just any real life circuit with the assumption of ideal wires, especially when high frequency AC signals are involved or significant magnetic effects are present
13) Kirchoffs voltage law does not contain an intergal of E as Dr. Lewin shows. Its actually a algebraic sum of all voltages on components and as such can only be used on a lumped model.

Aw, man! Don't do that. What do you think an integral is? You clearly have no idea that integrating the electric field along a path of lumped components will result exactly in the algebraic sum of all voltages on the components.

For the record, Richard Feynman and others use the line integral with lumped circuits to demonstrate Kirchhoff's law.

14) Kirchoffs cirucit laws do not go against Faradays law or Maxwells equations. All three can exist without conflict. Faradays law and KVL describe two different things and as such are not mutually exclusive.

If they describe two different things, they are mutually exclusive.

15) Kirchoffs citucit laws have nothing to do with Maxwells equations, but they are used together whenever circuit analysis is used on reactive components such as inductors or capacitors.

Kirchhoff's law can be deduced from Maxwell's equations. This is classic electromagnetism.

16) The circuit from Dr. Lewins experiment can easily be lump modeled using multiple coupled inductors to represent wires. As such all common methods of circuit analysis can be applied to it including KVL to get results matching the real physical experiment

No circuit under varying magnetic fields can be lumped modeled. Please read the Feynman lectures recommended by Mehdi.

I might have missed a few but these are the ones i remember right now. Any disagreement on these?

We are not here to reach an agreement. We are here to ascertain the truths of electromagnetism.

[Sredni]

And yet, the voltage between A and B can have two different values.

At the same exact time?

Yep. That's a snapshot at a given time.
The field will oscillate going one way, then the other, at - I do not remember exactly, maybe... 300 Hz?
At any rate, well within the limit of quasi static electrodynamics.

Maybe you have to take into account the magnetic field generated by the flowing current through the wire...

Nope, self-inductance is negligible, and there are no retardation effects.

The same two points, at the same moment in time, can have different voltages between them.
And there are no voltmeters, no probes, no measurement errors.
That's just the way it is.

Now, do I get to beat Mehdi, like in old Iran? 
What would Jesus do?

[Berni]

The "correct probing" is a technique to avoid UNWANTED induction. But Lewin's experiment is exactly to show how voltage is dependent on the path under induction. So the voltage induced by the probes is PART of the experiment. You cannot subtract it out!

If you set up an experiment and employ a probing technique to suppress the very effect you are trying to demonstrate, you are on dope.

Exactly it gets rid of unwanted effects such as the probe wires needing to follow a certain path, but it does not get rid of what you are measuring.

You still get the same result in Dr. Lewins experiment if you use the formal definition of voltage when subtracting out the probes. It just so happens that he set the probe wires in such a path that you need to subtract 0V to get the result. If you move the wires you get a diferent result on the voltmeters. Does that mean that the voltage across A and B has changed? No you just messed up your probing.

If you compensate out probing effects you can place both voltmeters on the left side in Dr. Lewins circuit and still get 2 different voltages as a result. If you do all your probe compensation math with textbook voltage you get two different values for voltage no matter where the voltmeters or the wires are.

If you use the "efective voltage" in the math to calculate the error voltage on the probes to subtract out you get the same result on both voltmeters no matter where they are. (Just like here you could just place one voltmeter in the middle for this error voltage to be 0V and thus make no need to compensate it out)

Correct probing practices don't break Dr. Lewins two voltages across A and B experiment, but given that the path the probe wires take in Dr. Lewins physical experiment is important it should be said why the probe wires take the path they do. This particular path requires no compensation of probe error for what he is trying to measure, all other paths do.

Aw, man! Don't do that. What do you think an integral is? You clearly have no idea that integrating the electric field along a path of lumped components will result exactly in the algebraic sum of all voltages on the components.

For the record, Richard Feynman and others use the line integral with lumped circuits to demonstrate Kirchhoff's law.

Well in the lecture where he talks about it he uses the summa operator:
http://www.feynmanlectures.caltech.edu/II_22.html#Ch22-S3

He also explains why analyzing circuits as lumped is a good idea in the section above the one linked.

If they describe two different things, they are mutually exclusive.

They would be mutually exclusive if they would explain the SAME thing as being two different things.

Kirchhoffs circuit laws describe voltage and current relationships in circuit meshes. Maxwells equations describe the relationships of electromagnetic fields in our universe.

Kirchhoff's law can be deduced from Maxwell's equations. This is classic electromagnetism.

You certainly can, here is how: https://physics.stackexchange.com/questions/102458/how-can-kvl-kcl-be-derived-from-maxwell-equations

However as you can see the equation you get as a result looks rather messy. This is sort of the physical world incarnation of Kirchhoffs law, but it does work with magnetic fields present, since the Maxwells equations that it came from also work fine with magnetic fields present.

Kirchhoff only stays so beautifully simple when you keep it within circuit meshes where it was meant to be used. Hence why it is so useful there.

No circuit under varying magnetic fields can be lumped modeled. Please read the Feynman lectures recommended by Mehdi.

I certainly agree for cases when the formal definition of voltage is used. Or in the case that you are not allowed to use coupled inductors in circuit models, i sure hope that is not the case since that makes modeling transformers really tricky (And Dr. Lewins experimental circuit is just a glorified transformer)

We are not here to reach an agreement. We are here to ascertain the truths of electromagnetism.

Well in that case we can close the thread cause Maxwell beat us to the goal of ascertaining the truths of electromagnetism by a good 150 years.

[Berni]

What probe wires???
There are no probes wires in the computation of the path integrals I've shown above.
The two different values we get, for the two possibile path along the circuit, are the result of induction. But that's how the system is. If you remove the induced part of the field, you are analyzing a different (unrealistic) system.

It's as if you subtracted the field generated by the point charge near a piece of copper to come to the conclusion that there is a nonzero field inside the metal (and then came up with tiny generators inside the metal) that produce the observed surface charge.

The ones that connect his oscilloscope to points A and B, since the BNC connector on a scope does not conveniently have the exact contact spacing to touch the two points of interest.

Im not saying that the two voltages result is due to the probe wires. I am trying to say that the path that the probe wires take is important. In Dr. Lewins experiment if you move the probe wires into different paths you get a different result on the oscilloscope, hence why understanding the effects of probing is important. The path his wires take in that case is such that the formal voltage difference between the voltage of interest and the scope terminals is zero. If you take probing into account you can run the wires in any path you want and get the same result. Still two voltages across A and B.

In the case of point charges this extra field eventually sorts it self out since its conservative so it adds up to zero once you get around the loop.

[bsfeechannel]

Now, do I get to beat Mehdi, like in old Iran? 
What would Jesus do?

Well, the first crucifixion recorded by history was performed by the Persians in 522 a.C. So I guess Jesus may be a little bit furious as of now.

While Jesus calms down, perhaps it's time for Mehdi to issue a huge apology to the engineering and scientific community for trying to give credit to pseudo-scientific claims.

[bsfeechannel]

Exactly it gets rid of unwanted effects such as the probe wires needing to follow a certain path, but it does not get rid of what you are measuring.

You still get the same result in Dr. Lewins experiment if you use the formal definition of voltage when subtracting out the probes. It just so happens that he set the probe wires in such a path that you need to subtract 0V to get the result. If you move the wires you get a diferent result on the voltmeters. Does that mean that the voltage across A and B has changed? No you just messed up your probing.

Here resides all your struggle with reality.

When you "right-probe" something you are not aware that what you are doing is exactly to make your probes follow a certain path.

In Lewin's experiment, we have a WANTED field. This is the field that's generating the EMF to power the resistors. So if you "right-probe" that circuit you will cancel out the effect of this EMF on your meter, treating this field as UNWANTED, and you are going measure nonsense.

If you compensate out probing effects you can place both voltmeters on the left side in Dr. Lewins circuit and still get 2 different voltages as a result. If you do all your probe compensation math with textbook voltage you get two different values for voltage no matter where the voltmeters or the wires are.

If you use the "efective voltage" in the math to calculate the error voltage on the probes to subtract out you get the same result on both voltmeters no matter where they are. (Just like here you could just place one voltmeter in the middle for this error voltage to be 0V and thus make no need to compensate it out)

Correct probing practices don't break Dr. Lewins two voltages across A and B experiment, but given that the path the probe wires take in Dr. Lewins physical experiment is important it should be said why the probe wires take the path they do. This particular path requires no compensation of probe error for what he is trying to measure, all other paths do.

And what is the significance of that voltage? Is it the EMF? No. Is it the voltage across one of the components? No. It's just an arbitrary voltage defined by an arbitrarily precise positioning of your probes. And that's exactly what Lewin wanted to prove.

You are confounding the concept with the technique. You take the "right probing" technique as a dogma, and you think that the technique can overrule the concept that created it. Unbelievable!

Well in the lecture where he talks about it he uses the summa operator:
http://www.feynmanlectures.caltech.edu/II_22.html#Ch22-S3

Yes. He does.



And what is on the left side of the equals sign? A sea horse? A pregnant, elongated, slanted S? Or is it a line integral?

Any five year old kid knows that two things separated by an equals sign are equivalent. So the algebraic sum of the voltages around a circuit is equal to the line integral of the electric field around the path determined by the circuit (in the case where there are no varying fields as Feynman explains earlier).

He also explains why analyzing circuits as lumped is a good idea in the section above the one linked.

Provided you can LUMP THEM! You can only lump model a circuit if, and I quote, there is no magnetic field in the region outside the individual circuit elements. It's in the text. Didn't you read it? Or you need us to repeat it to you like a broken record every day? If you want to know why, read Feynman's previous chapters.

Lewin's circuit HAS a magnetic field outside the components, so it is UNLUMPABLE.

They would be mutually exclusive if they would explain the SAME thing as being two different things.

The text you linked is cool because it is here where Feynman derives Kirchhoff from Maxwell, showing that Kirchhoff is just a special case. All the complicated math he had already done in the previous chapters to come right to this point.

So you cannot argue anymore that Kirchhoff is one thing and Maxwell another. The proof is in the pudding.

Kirchhoffs circuit laws describe voltage and current relationships in circuit meshes. Maxwells equations describe the relationships of electromagnetic fields in our universe.

And where do you think our circuit meshes live? Outside the universe? Perhaps in the heavens? I can't believe I'm reading this.

You certainly can, here is how: https://physics.stackexchange.com/questions/102458/how-can-kvl-kcl-be-derived-from-maxwell-equations

However as you can see the equation you get as a result looks rather messy. This is sort of the physical world incarnation of Kirchhoffs law, but it does work with magnetic fields present, since the Maxwells equations that it came from also work fine with magnetic fields present.

So we do have two Kirchhoff's laws now? One version is the "physical world incarnation of" it. The other is the regular one.

We have then three valid theories to describe exactly the same phenomenon: Maxwell, "physical" Kirchhoff and "regular" Kirchhoff. Wow! 

Kirchhoff only stays so beautifully simple when you keep it within circuit meshes where it was meant to be used. Hence why it is so useful there.

Wouldn't be beautifully simpler if we could understand that there's ONLY ONE theory to describe electricity and magnetism: Maxwell, and that Kirchhoff is just special case of it?

I certainly agree for cases when the formal definition of voltage is used.

Your brain has already realized that the cozy shell you created around your thoughts are no longer holding the water. The clear sign of it is the invention of the "effective voltage", "textbook-defined voltage", "physical Kirchhoff", "good probing technique" and other mental bodges to conciliate your set of axioms with the conflicting reality.

This thread is interminable because every time you try to make sense of your "theory" someone shows you a contradiction.

A theory can only hold if it is not contradictory.

Get rid of this as soon as possible, before someone gets hurt (including yourself).

Or in the case that you are not allowed to use coupled inductors in circuit models, i sure hope that is not the case since that makes modeling transformers really tricky (And Dr. Lewins experimental circuit is just a glorified transformer)

Every animal is vulnerable during the molt process. That happens to us when we need to get rid of concepts we thought were truths but aren't. Give time to yourself. Learn Maxwell piecemeal.

Well in that case we can close the thread cause Maxwell beat us to the goal of ascertaining the truths of electromagnetism by a good 150 years.

Cool! That's what I'm trying to do since 28 November when I told ogden to get better education (and I was subsequently called a troll). What we need to do now is to shut up and learn Maxwell (me included).

[Sredni]

Now, do I get to beat Mehdi, like in old Iran? 
What would Jesus do?

Well, the first crucifixion recorded by history was performed by the Persians in 522 a.C. So I guess Jesus may be a little bit furious as of now.

WHAT? IT'S MEHDI'S FAULT JESUS WAS KILLED???
GET HIM!

Jokes aside, I did not want to start a real religion war.
Maybe we should set for 100 lashes with a wet noodle.
But first I have to tie a few loose ends, and fix the signs in my integrals (also, I have to remove that circle from all surface integrals, what was I thinking?). Who knows, maybe I'll be able to convince Berni...

As you said, we have all had our Maxwell crisis. It has to take its course.

[bsfeechannel]

Maybe we should set for 100 lashes with a wet noodle.

Paraphrasing Get Smart, zis is EEVblog, ve don't lash here (I always wanted to use that catch phrase).

For those who will read this thread in the years to come it is good to make it clear that Sredni's joke is a reference to Mehdi's joke in one of his videos about not living in Iran and thus being exempt from corporal punishment and about the fact that Youtube is banned there.

Mehdi's claims about Kirchhoff's laws were promptly and peremptorily debunked by serious understanding of physics and engineering. That's how we "punish" around here.

[ogden]

Cool! That's what I'm trying to do since 28 November when I told ogden to get better education (and I was subsequently called a troll).

You think you are not worthy of this title? Look for yourself how many times you managed to insult Berni in single post! You were bitterly arrogant against him through most of this discussion, yet he never pushed back

[CM800]

Arguing about unwanted and wanted fields... putting the 'P' in PhD.

I side with Mehdi on this.

The fields are effecting the probes, the only reason why the voltage changes is due to how the probe wires are affected by the probes. In such a way the laws are put in place, we talk of an ideal circuit.

If I was to make the same mistake while trying to measure a current sensor's voltage while wrapping the wires around the probe, I'd be laughed out of the room.

[bsfeechannel]

You think you are not worthy of this title? Look for yourself how many times you managed to insult Berni in single post! You were bitterly arrogant against him through most of this discussion, yet he never pushed back

When Berni shows that you can deduce Kirchhoff from Maxwell and says that Kirchhoff doesn't have anything to do with Maxwell, it insults my intelligence. And makes me very angry.

It insults the intelligence of any reader of this forum.

Instead of sayin, hey, you know, I have a little difficulty understanding electromagnetism, could you help me with this? Or, I always thought that Kirchhoff always holds, can you explain why it isn't so? He keeps blurting stupid assertions like that to justify his gross errors and misconceptions and absolute lack of study of one of the staples of EE.

Sredni, I and others voluntarily spend time to try to bring the most accurate and didactic explanations.

So, who is arrogant? Who is the troll? Someone who makes personal sacrifices and sincerely wants to help a fellow engineer stop espousing nonsense, or someone who refuses to learn and on top of that invents the most incoherent excuses again and again to remain in ignorance?

I have a lot to learn about Maxwell and electromagnetism, but instead of  transforming my ignorance in some kind of precept to publish on forums, I do what you and Berni should do: I try to learn.