Does Kirchhoff's Law Hold? Disagreeing with a Master

[EEVblog]

....

You continue to think being an arrogant intellectual bully who time and again resorted to petty name calling and demeaning anyone not totally agreeing with you is a credible Scientific or Engineering method. On any level and as I mentioned a long while ago would not be tolerated in most workplaces or institutions of learning.

In this thread is some great reading but so much useless non Science and Engineering and OTT Ego driven non debate.

Play the science and engineering not play the man!

Wait a minute! Dave can say that he didn't follow the thread and that he doesn't respect Lewin based on mere impressions. I discussed the theme exhaustively, concluded, not decided, that Lewin deserves our respect and Mehdi doesn't and I am an arrogant intellectual bully?

I didn't attack people, an entire channel's audience, and members on this forum.

Is that because I cared to study, read, read again, check, double check, watch Mehdi's videos more times than any of his own subscribes,  watch Lewins videos the same number of times, just to ascertain the truth?

Bingo.
You make it sound like all this is so plainly obvious, that it's all obviously settled, and "how dimwitted Mehdi's audience is for not noticing this", that Mehdi " do not deserve our respect and should not be addressed as engineers".
Yet here you are saying that it took you all this effort to figure it all out watching the video countless times, reading, re-reading, studying, double checking etc 
And now we are simply take your word for it that this it's all settled and it's obvious Mehdi is completely wrong on every point etc, so much so that we shouldn't respect him as an engineer?
Sorry, but I'm going to play along with that.

This is not a trivial argument that even the most experienced and well educated engineers understand, in fact the argument has been going on decades.
Mehdi had every right to question Lewin's experiment, because without excruciatingly detailed investigation it seems like a dodgy setup to demonstrate his point.
And from what I can see there still seems to be debate on this forum about the exact applicability and implementation of the demonstration.
And from what I saw in Lewin's videos he didn't really even attempt to break down and explain clearly and simply why Mehdi is wrong on all his points. If he did then you and a couple of others wouldn't have  had to have spent, what, maybe a hundred or two man-hours trying to break this down and debate and explain it?

[ogden]

Depends, 2 minutes ago I interrupted a conversation between my manager and a colleague to point out that they are trying to talk about how to put holes in metal work for wiring before we have even agreed the wiring (that i will have to design). Am I superior? yes I am! The world is full of dumb people that call themselves engineers because they do drawings. Doing drawings and designing are two entirely different things.

It is a matter of perspective. *You* may think that knowledge of hole drilling/cutting/punching/whatever is needed *only* in case when *you* design wiring that requires holes. What if one of them wanted to show off his knowledge (to you or other guy). What if one of them thought - I know how it shall be done, let's tell it now disregarding he will need it or not. In both cases I would find discussion about holes reasonable and not dumb.

[Simon]

no it was a silly discussion about do we need to power 2 devices on one wire or separately. The electrical architecture has not yet been designed yet they are trying to finalise the metalwork

[Berni]

Kirchhoff's laws were meant to explain the underlying physics. Read Kirchhoff's original paper posted by seagreh. If you can't read German, cross the border and kindly ask an Austrian inhabitant to read it for you.

So if KVL is for the birds then the entirety of circuit analysis theory is for the bids as well. I'm sure any proper electronics engineer will disagree because circuit analysis has served them well ever since learning it in school.

Kirchhoff is for the birds means that Kirchhoff is not a fundamental law. Just that. Be prepared to see it being violated repeatedly. It just means that circuit analysis has its limits. It cannot be used for every kind of circuit. And you have to know when it is not applicable.

I bet SPICE didn't tell you that.

So please circuit analysis for explaining circuits and not physics.

Circuit analysis is physics.

Yes at the time it was the best explanation for this wonderful newfangled electricity thing so it was adopted as a theory of electricity. Just like we thought that light is continuous and that neutrons, protons and electrons are the most fundamental buildings blocks, today we know that's wrong, but 100 years ago we had no idea. Even today we can't know for sure if certain things we assume as fact are actually true.

Circuit theory is just a practical application of Physics. Much like Physics is a practical application of Math.



So you still haven't answered me what is the correct way to analyze the circuit in this post:
https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2189216/#msg2189216

If we can't use circuit analysis, then what do we use to determine what it does?

[bsfeechannel]

I didn't attack people, an entire channel's audience, and members on this forum.

What member of this forum am I attacking?

Anyway, the first time I heard the term "audiophool" was from you. I thought that those were tagged with that moniker because, as the name suggests, they aren't considered exactly smart people. Then I came across the "idiot assembler (sic) programmers" (EEVBlog#45). Perhaps that was just a joke that I missed, but then you compared the faith of religious people with the beliefs of the audiophools (EEVBlog#833 @38:05), which I totally agree. For the record I'm not a religious audiophile assembly programmer, but those examples encouraged me to give names to people who cannot, or do not want to, accept that their claims are bullshit, especially in light of scientific evidence. It is clear now that this move only proved that I'm wrong. I should have foreseen it. It was my fault. Sorry about that.

You make it sound like all this is so plainly obvious, that it's all obviously settled, and "how dimwitted Mehdi's audience is for not noticing this", that Mehdi " do not deserve our respect and should not be addressed as engineers".
Yet here you are saying that it took you all this effort to figure it all out watching the video countless times, reading, re-reading, studying, double checking etc 

I make it sound obvious because I understood Lewin's answer as soon as he posted his first video in response to Mehdi's first video (the one you posted). However, when Mehdi posted his second video, implying that Lewin has wrong "beliefs" about electromagnetism because they were divergent from Mehdi's own wrong conclusions; asserting categorically that Kirchhoff holds for varying magnetic fields; and claiming that Feynman and Belcher agree with him, among countless other false claims, we had to go deeper into the subject and debunk point for point. Not to say about Mabilde's videos and other false claims from members of this forum. This only strengthened our understanding of Lewin's answer.

You obviously don't need to do all that research we did to solve Lewin's exercise.

And now we are simply take your word for it that this it's all settled and it's obvious Mehdi is completely wrong on every point etc, so much so that we shouldn't respect him as an engineer?

Sorry, but I'm going to play along with that.

You should never take my word for it. Go out and investigate for yourself. I learned those words with a famous video blogger which I really respect (exactly because of those words). Please feel free to check the video references, the references in Feynman's lectures. Draw your own conclusions. I'm just pointing things out (together with expressing my opinion, albeit not exactly popular, I can see it now).

This is not a trivial argument that even the most experienced and well educated engineers understand, in fact the argument has been going on decades.

This discussion was settled long ago. Lewin's experiment is in fact right. The "discussion" keeps going on because people insist that KVL holds for any circuit. But this is an illusion provided by the fact that Kirchhoff's laws, or better saying the modern version of it, can be applied to an awful lot of circuits under certain special conditions that we take for granted.

When this circumstances fail, Kirchhoff (KVL, KCL or both) is not valid anymore. You have to resort to Maxwell's equations. Lewin's is one of those circuits. Transformers, inductors, generators, motors, transmission lines, antennas, etc. can only be explained by the same approach.

Lewin's experiment is all about identifying exactly when and where Kirchhoff's laws fail. We have but to thank him eternally for that.

Mehdi had every right to question Lewin's experiment, because without excruciatingly detailed investigation it seems like a dodgy setup to demonstrate his point.

Mehdi has the right to question. But his second video is not about questioning. It is about decreeing his (lack of) understanding as a proof of his "theorem". He even ends his video writing the words Q.E.D.

We did what you recommended and didn't take his word for it. We went out and investigated for ourselves and the result was not pretty I'm afraid.

And from what I can see there still seems to be debate on this forum about the exact applicability and implementation of the demonstration.
And from what I saw in Lewin's videos he didn't really even attempt to break down and explain why Mehdi is wrong.

I think Lewin did. It is clear to me. But if you believe Lewin didn't, rest assured we did. It is exactly this thread. Please stay around. We perhaps have some more debunking to do, which will make it all very clear to you, I guess.

Although I must confess, I'm running out of time to contribute lately. I only decided to stop by because of the shocking news of Sredni's banning. At a certain point I thought of doing a video entitled "Debunking the debunkers: why Mehdi and Mabilde are wrong and Lewin is right." or something like that. But first I need to find time.

[bsfeechannel]

Kirchhoff did not say

Σ Vk = 0
 
But he basically said, the sum of voltage drops (he expressed as product of resistance and current) equals to the sum of EMFs.

Absolutely correct.

Kirchhoff says:

[...]nennen wir [...] die elektromotorische Kraft, die ihren Sitz in der Berührungsstelle dieses und des folgenden Drahtes hat, K_i [...]

Let's call the electromotive force, that has its place between this [wire i] and the following wire, K_i.

[...] wenn die Drähte 1, 2, ...ν eine geschlossene Figur bilden,[...]

If the wires 1, 2, ... ν form a closed figure,

[...]so können wir diese Gleichung schreiben:

I₁.ω₁ + I₂.ω₂ + ... + I_ν.ω_ν = K₁ + K₂ ... + K_ν

then we can write this equation:

I₁.ω₁ + I₂.ω₂ + ... + I_ν.ω_ν = K₁ + K₂ ... + K_ν

[...]wo, ω₁, ω₂, ... die Widerstände der Drähte, I₁, I₂ ... die Intensitäten der Ströme bezeichnen[...]

where, ω₁, ω₂, ... designate the resistance of the wires, I₁, I₂ ... designate the current intensities.

There you have it. Straight from the horse's mouth.

Now let's take the open secondary of a transformer, for example, comprised of a single turn. This experiment is very easy to reproduce with a linear transformer (I did that using a MOT).

Since the loop is open the current in the wire is zero. The EMF is 1V (my MOT can give me 600mV for a single turn). Applying Kirchhoff's law using exactly the terminology of his seminal paper we have:



an absurd.

[ogden]

Now let's take the open secondary of a transformer, for example, comprised of a single turn. This experiment is very easy to reproduce with a linear transformer (I did that using a MOT).

Since the loop is open the current in the wire is zero. The EMF is 1V (my MOT can give me 600mV for a single turn). Applying Kirchhoff's law using exactly the terminology of his seminal paper we have:

an absurd.

Absurd indeed. -  To apply Kirchoff's Circuit Law (Kirchoff's loop rule) to EMF source alone, w/o actual circuit or loop. 

[bsfeechannel]

Absurd indeed. -  To apply Kirchoff's Circuit Law (Kirchoff's loop rule) to EMF source alone, w/o actual circuit or loop. 

Alright. Let's close the circuit.

Since there is no EMF between the point of contacts of the two wires (Kirchhoff is adamant about that) K₁ + K₂ ... + K_ν = 0V. Then we have:



another absurd.

[ogden]

another absurd.

You can't even apply Maxwell's equation correctly, use I*R instead. - That's absurd.
[edit] After all this time you did not learn that sum of all fields means sum of all types of the fields - conservative and non-conservative.
[edit] Also you do not seem to discern two voltages - voltage through the inductor and voltage across the inductor. One (I*R) is zero if R=0 but another is EMF, -L(di/dt) .
[edit] Correct equation is I1*R1+I2*R2+(-L(di/dt))=0.

[rfeecs]

The difference between a purely electrostatic field and one induced by a magnetic field is the non conservative part. This gives the field ability to push electrons around closed loops of conductor while a electrostatic field can only redistribute them but not sustain a current apart from the very brief transient as they redistribute.

Since the inner conductor forms a continuous loop trough the voltmeter, it means that the the field can push the electrons around it and create a current that the voltmeter detects as voltage across its internal resistance. The shield however does not form a continuous loop and as such can't experience any current trough it.

I don't see why you would need current to shield a static electric field.

...My point is that the coax shield in this configuration has no effect.

I'm not convinced.  I expect the coax will shield the center conductor from the induced electric field.  So you would measure the same voltage whether the scope was on the left or the right side.

OK, I'm convinced.  I tried it.  The coax doesn't do a damn thing.

You are right.

My new explanation, pretty much the same as yours, is the induced field component that causes the current is parallel to the wire.  Putting a coaxial shield parallel to the field does nothing.

So even though there is no magnetic field in the region of the test leads, only the induced electric field, you can't shield them with only a conductive shield.

[bsfeechannel]

[edit] Correct equation is I1*R1+I2*R2+(-L(di/dt))=0.

Since i is constant in my example di/dt is zero  (or next to it if you consider a very low current at a low frequency).

So  I1*R1  +  I2*R2 =0, 1V = 0V !!.  The absurd remains the same.

But today is your lucky day. I'll show you how Kirchhoff fails once more. There are infinite ways to show that Kirchhoff doesn't hold. I could do this the whole day. It's a shame that I am not paid for that. Perhaps I'll open a Patreon account and ask people to help me debunk this pseudo scientific claim.

Anyway, in the circuit below I connect a battery, but if you don't like it, you can connect a generator, that produces the same voltage of the EMF. Of course the current is going to be zero. See what happens.



Faraday 3 x Kirchhoff 0

[Berni]

OK, I'm convinced.  I tried it.  The coax doesn't do a damn thing.

You are right.

My new explanation, pretty much the same as yours, is the induced field component that causes the current is parallel to the wire.  Putting a coaxial shield parallel to the field does nothing.

So even though there is no magnetic field in the region of the test leads, only the induced electric field, you can't shield them with only a conductive shield.

Awesome to see the experiment done for real.

To be fair if i was asked the same question at the very beginning of the tread i would have likely expected the coax to shield it too, that's what the job of the shield on a coax is after all. But magnetic fields can be sneaky sometimes.

[edit] Correct equation is I1*R1+I2*R2+(-L(di/dt))=0.

Since i is constant in my example di/dt is zero  (or next to it if you consider a very low current at a low frequency).

So  I1*R1  +  I2*R2 =0, 1V = 0V !!.  The absurd remains the same.

But today is your lucky day. I'll show you how Kirchhoff fails once more. There are infinite ways to show that Kirchhoff doesn't hold. I could do this the whole day. It's a shame that I am not paid for that. Perhaps I'll open a Patreon account and ask people to help me debunk this pseudo scientific claim.

Anyway, in the circuit below I connect a battery, but if you don't like it, you can connect a generator, that produces the same voltage of the EMF. Of course the current is going to be zero. See what happens.



Faraday 3 x Kirchhoff 0

But you can still get 0V or 1V depending on what path you take trough the circuit in the case of Maxwell. So you can just as well turn it around and show the opposite by always choosing the voltage that does agree to KVL. So is then KVL in a quantum superposition of being dead and alive at the same time?

We all know you can't use KVL in varying magnetic fields, so why do you keep trying to prove it? My claim is that it always works in LUMPED circuit meshes.

So if you want KVL to work then lump model the whole thing and it will work fine, mixing lumped and non lumped models wont work.

[ogden]

[edit] Correct equation is I1*R1+I2*R2+(-L(di/dt))=0.

Since i is constant in my example di/dt is zero  (or next to it if you consider a very low current at a low frequency).

So  I1*R1  +  I2*R2 =0, 1V = 0V !!.  The absurd remains the same.

You do not seem to comprehend momentary current as well. 

di is zero *only* at very beginning of the pulse. After some time elapsed meaning dt is not zero anymore, di is not zero as well.

Before you talk about Maxwell equations, make sure you understand elementary physics.

[edit] -L(di/dt) is Maxwell's equation. We agreed that result (EMF) is 1V long ago. So what you think about di is irrelevant, you simply put -1V in the equation: 0.1V + 0.9V - 1V = 0. KVL holds.

[bsfeechannel]

So is then KVL in a quantum superposition of being dead and alive at the same time?

If we choose the same path, we'll get the same voltage. Maxwell/Kirchhoff is still classical physics. Ironically in their time the seeds for quantum mechanics were already planted by no one less than Kirchhoff himself with his study of the black-body radiation. Max Planck was one of his students and the rest is history.

We all know you can't use KVL in varying magnetic fields, so why do you keep trying to prove it?

I did that to reply to a post that claimed that Kirchhoff didn't say that Σ Vk = 0, but that the sum of voltage drops, expressed as the product of resistances and currents, equals to the sum of EMFs.

I proved that, even if you use Kirchhoff's terminology, instead of our modern, KVL doesn't hold for varying magnetic fields. Kirchhoff's version of his own law implies certain assumptions and conventions (explicitly stated in his thesis) that render the same result.

But then, ogden intervened, which is always amusing and didactic I must say.

[bsfeechannel]

you simply put -1V in the equation: 0.1V + 0.9V - 1V = 0.

You put -1V there and explicitly violate Kirchhoff' law.

Before you talk about Maxwell equations, make sure you understand elementary physics.

Learning German and reading Kirchhoff's original paper also helps.

[ogden]

you simply put -1V in the equation: 0.1V + 0.9V - 1V = 0.

You put -1V there and explicitly violates Kirchhoff' law.

You mistakenly think so because as you already demonstrated, you do not comprehend what di/dt and "current at the time of observation" means. I am not sure that you fully understand conservative and non-conservative fields as well. Any clue that they differ and you have to take in account all fields? Your original formula "I1*R1+I2*R2=0" did not include EMF, so I corrected it: I1*R1+I2*R2+(-L(di/dt))=0.

[bsfeechannel]

You mistakenly think so because as you already demonstrated, you do not comprehend what di/dt and "current at the time of observation" means.

Well, I may not understand a lot of things, but you surely don't know the difference between an inductor and a generator. Please, read this.

I am not sure that you fully understand conservative and non-conservative fields as well.

You could say that if there were a conservative magnetic field there.

Any clue that they differ and you have to take in account all fields? Your original formula "I1*R1+I2*R2=0" did not include EMF, so I corrected it: I1*R1+I2*R2+(-L(di/dt))=0.

Although it would be nice to take credit for Kirchhoff's work and say that the formula is mine, we'd better not only attribute it to Kirchhoff but also not try to surreptitiously and clandestinely sneak "corrections" into it.

[bsfeechannel]

A little rant to feed our thoughts.

No, not at all. At least I hugely respect your work on studying, checking, and explaining; I believe others respect it as well.

All the namecalling (like the flat-earther shit), roasting inbetween is what people don't like. It's called "bullying". But I think you have been getting better during the thread. Try to keep on the subject, try to be less condescending, and you'll do fine. You are not superior. If you feel like others are really dumb, you are often not seeing something.

Social constructs can be difficult sometimes.

Dave has an interesting recent video about how to become an engineer. He pointed out, and people confirmed in the discussions, that what is considered an engineer varies from country to country due to culture, legislation, economical environment, etc.

To me, an engineer professing pseudo-scientific claims (which is different from questioning), or advocating deficient knowledge as an advantage, especially at the expense of the reputation of another professional is morally appalling.

Besides, I am an old fart. While we already had SPICE around, back in my day we were taught to use our brains.

Simulation software in the hands of an engineer who does not master the fundamentals is the recipe for disaster, my experience showed.

So, the "flat-earther shit" is the result of being repeatedly exposed to what I consider an aggression to my standards and is not an expression of condescension, but of exasperation, which is not a good feeling.

Even Lewin managed to apologize for an earlier video retort to Mehdi and if this socially flawed human can manage that there may be hope for you too.

This is a total inversion of values. The savvy have to apologize to the ignorant for being savvy. Almost makes you discourage to seek knowledge.

Dr. House has a politically incorrect quote: "Yesterday's sluts are today's empowered women. Today's sluts are celebrities."

The ignorant of today are celebrities.

[unitedatoms]

Great video by Electroboom. Lewin is mixing models in wrong way.

In my humble opinion, The circuit laws apply only to pure sizeless graphs of lumped sizeless components connected with sizeless lossless equipotential wires conducting with infinite speed. Whole modeled circuit has total volume of zero cubic microns and completely electroneutral and disconnected from rest of universe. No fields of any kind are present.

[beanflying]

A little rant to feed our thoughts.
....

A load of self indulgent WAFFLE to justify your ongoing poor behavior toward others. Lewin rightly apologized for the personal attack on Mehdi as regards his background and training and rightly not for what he sees as errors of the technicalities as is appropriate. He certainly never ranted te word 'Liar' as you have done and went about explaining what he thought was incorrect.

You clearly and incorrectly draw no distinction between those two things. On multiple ocasions at a minimum you have told members to 'get an education' which is simple Baiting, Bullying or being simply demeaning to them and not to their position on the subject under discussion.

Are you a 'Bad Person' - others can draw their own conclusions.

[jesuscf]

Great video by Electroboom. Lewin is mixing models in wrong way.

In my humble opinion, The circuit laws apply only to pure sizeless graphs of lumped sizeless components connected with sizeless lossless equipotential wires conducting with infinite speed. Whole modeled circuit has total volume of zero cubic microns and completely electroneutral and disconnected from rest of universe. No fields of any kind are present.

What about transmission lines?

[unitedatoms]

What about transmission lines?

The transmission lines are OK to consider sizeless too. They are not special case. Absolutism of model requires everything to be a net component, but does not limit complexity. So lines are infinitely fragmented chains of LCRG parts with characteristic values expressed in Ohms, Farads, Henries and Siemenses like the rest of simple components.

One may notice how slow Spice becomes when it has line in the model.

[EEVblog]

To me, an engineer professing pseudo-scientific claims (which is different from questioning), or advocating deficient knowledge as an advantage, especially at the expense of the reputation of another professional is morally appalling.

Who the hell is advocating for "deficient knowledge" as being an advantage?

This is a total inversion of values. The savvy have to apologize to the ignorant for being savvy. Almost makes you discourage to seek knowledge.

You don't have to apologise for anything, no one has a gun to your head demanding that. But people are free to think of you and the way you express yourself in any way they like, including having a not so good opinion of you.

[EEVblog]

You should never take my word for it. Go out and investigate for yourself. I learned those words with a famous video blogger which I really respect (exactly because of those words). Please feel free to check the video references, the references in Feynman's lectures. Draw your own conclusions. I'm just pointing things out (together with expressing my opinion, albeit not exactly popular, I can see it now).

You're damn right it's not popular.
When you say that Mehdi "should not be addressed as (an) engineer", you aren't going to win many friends on here.
Not to mention calling Mehdi's audience "dimwitted"

[Berni]

What about transmission lines?

Yep a transmission line is what is used to model that travel time in lumped circuits. The actual implementation of a transmission line probably varies a bit, but for simulators you usually specify a characteristic impedance and propagation delay.


And yeah SPICE does not do any of the thinking for you. Its the users responsibility for giving it a accurate circuit model so you still need to know what you are doing. So why would spice be bad? Its just a programatical implementation of existing circuit analysis theory.