Author Topic: Does Kirchhoff's Law Hold? Disagreeing with a Master  (Read 95846 times)

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ogden

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #925 on: February 21, 2019, 05:40:49 am »
Non-essential properties you say!  Go tell that to the electrical engineers of your local power utility and watch their reaction.  If reading the book I recommended is out of your reach, try watching a PBS documentary from the series American Experience about the first trans Atlantic cable.  I think YouTube has it.

Instead of offering me read that book maybe you can read it yourself? Please show me how transmission line DC resistance property relates to what I was talking about in my example? You may start with velocity factor formula and check where you put DC resistance in. Anywhere?

 It does not add to the discussion about wavelengths in the cable if you are trolling about how big attenuation will be in 195km cable or how hugely expensive it will be. It does not matter in the context!
« Last Edit: February 21, 2019, 06:52:42 am by ogden »

jesuscf

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #926 on: February 21, 2019, 07:56:53 am »
Non-essential properties you say!  Go tell that to the electrical engineers of your local power utility and watch their reaction.  If reading the book I recommended is out of your reach, try watching a PBS documentary from the series American Experience about the first trans Atlantic cable.  I think YouTube has it.

Instead of offering me read that book maybe you can read it yourself? Please show me how transmission line DC resistance property relates to what I was talking about in my example? You may start with velocity factor formula and check where you put DC resistance in. Anywhere?

 It does not add to the discussion about wavelengths in the cable if you are trolling about how big attenuation will be in 195km cable or how hugely expensive it will be. It does not matter in the context!

Your example is fundamentally flawed because you failed to properly model the elements of the circuit before attempting to analyzed it.  Hence you incorrectly concluded that Kirchhoff's laws didn't work.  I was just trying to show you how to properly model the elements of the circuit you proposed.  That includes the attenuation of the transmission line.  When you model all the elements of your circuit correctly then Kirchoff's laws do work!

It is the same with Dr. Lewin's demonstration.  He conducted an experiment.  The results of the experiment allegedly didn't match the laws of circuit theory.  Hence he concluded that the laws of circuit theory didn't work under the conditions of the experiment.  Along comes Mehdi (electroboom) and points out that important mistakes or omissions were made with the measurements and modeling of the circuit in Dr. Lewin's experiment.  Then Mehdi both models the circuit correctly and performs sensible measurements that prove that indeed the laws of circuit theory work.
Homer: Kids, there's three ways to do things; the right way, the wrong way and the Max Power way!
Bart: Isn't that the wrong way?
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ogden

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #927 on: February 21, 2019, 10:34:27 am »
Your example is fundamentally flawed because you failed to properly model the elements of the circuit before attempting to analyzed it.

Your logic is flawed or you are trying to shift goalposts, again.

I used model described in example on purpose - to simply demonstrate case where KVL does not apply and explain what I did mean by "non-uniform current". I did explain it already, pay close attention to fact that proper modeling of transmission line as precondition for KVL is mentioned as well:

Indeed sorry - that many including you, ignored or missed purpose of my "195km transmission line" example: to illustrate how transmission line works and how it can be that current is not uniform trough the length of the circuit/loop. Obviosuly to apply KVL, we have to do something with that line  - either lower working frequency or use it's lumped elements model.

In case this explanation still does not work for you - fine. I am ready to simply agree on disagreement.

Quote
When you model all the elements of your circuit correctly then Kirchoff's laws do work!

Yes I know. I confirmed that directly and indirectly here in this forum countless times. I am on your side - in case picking sides is important for you
« Last Edit: February 21, 2019, 11:05:35 pm by ogden »

bsfeechannel

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #928 on: February 21, 2019, 03:03:32 pm »
It is interesting to note that those who say that modeling your circuit "correctly" Kirchhoff always holds can never agree with each other. And have to take sides.

Those of us who care to study electromagnetism always agree with each other: I agree with Sredni, who agrees with Feynman, who agrees with Maxwell who agrees with Faraday.

There's never any animosity or name calling between us. Quite the opposite: we always thank each other for helping us have an even deeper understanding of physics because we know that this will make us better and more efficient design engineers and will save us the embarrassment of advocating pseudo scientific claims.

Where people refuse to accept the truth there can never be rational thinking.

Sredni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #929 on: March 05, 2019, 07:44:40 am »
post 2 of 3
(posted out of order for reasons to be explained in post 1 of 3)

On Kirchhoffians

Quote from: EEVBlog
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?

No, the concept is pretty simple (even though its implications can be counterintuitive, much like with the postulates of special relativity). What is difficult is trying to explain to people who do not have the prerequisites for understanding it (and/or have no intention to remedy that situation).

When you place a voltmeter in the Romer-Lewin circuit the mesh who is linking the flux has the bigger or smaller resistor in it, depending on where you place it. That's why you see different voltage depending on where you put the voltmeter.

But no, meshes are not good, if you use the seesaw line to represent resistor, they get confused and think everything should be lumped, so where is the primary of the transformer? Surely it will spring out when they apply Faraday from scratch using the integrals.

There are integrals, so  you need areas, and areas have boundaries, there is an inside and an outside. Depending on where the varying magnetic field happens to be (inside or outside?) you get a different result.

But no, areas are not good, they feel they can compute everything pointwise, on open paths and with undefined areas. So they want to go full Field.

Field theory
Maxwell's equations are not algebraic vector equations: they are partial differential equations. You need boundary conditions to go along with them. One can try to explain how rotor and divergence are related to circulation and flux and that you still need elementary areas and relative closed boundaries. That the total electric field along an open segment of your circuit is not uniquely determined by the segment itself, it depends on the rest of the circuit (or lack thereof)  because the circuit path as a whole is setting the boundary conditions.

But no, they still think they can split the solution on separate segments irregardless of what happens on the rest of the closed path, basically trying to define the inside and outside of an open curve. And even when you show that it is not the case because it would lead to wrong results, their conclusion is that their method is not wrong, it's just a 'bit off'. As if it were a numerical approximation error.
When you insist they produce a drawing of their closed-open curve, the discussion "becomes a bit heated" and you get banned.

And it never ends. They will always find some new twist.
Recently they mentioned transmission lines. They do not care when a system can be modeled by a transmission line, they just proceed by analogy: there's something that looks like a cable, and a model that has many inductances (and something else they do not care about) that represents its behavior. So, since the Romer-Lewin ring has some copper cable in it, it must certainly be that. Do you think they ever bothered to ask themselves what behavior is being modeled  in a transmission line?

Same goes for the equivalent circuit of a transformer that was brought up lately: it should model the behavior as seen from the terminals, but they don't care. They see that a transformer - which is basically two pieces of wire wound around something - has an equivalent circuit (as seen from the terminals) with many lumped components and think "That must be it!". They incorrectly infer that the lumped model must be what shows the voltages and currents inside the piece of wire!

This is plug and chug mentality, mixed with cargo cult science.
The root of the problem is the same: there are people who do not know when a certain model (a model other people, who actually studied the matter, have developed, refined and made so simple even a ten year old can apply it) can be used. Even worse: they have been taught what the limits of the model are, but they either forgot or do not care.

They twist reality to suit it to their warped, Aristotelian, thinking.
And, no, apparently you cannot even tell them to get an education because that is bullying.
You have to apologize, especially if the ignorant person that refuses to learn and persist in their error is a nice guy. So Lewin is the terrible human being who finally realized his godawful error: telling a youtuber to go study basic physics. Because Mehdi is wrong, and Lewin is right (you said so yourself: "I don't think anyone doubts that Lewin is ultimately right (he is)"), and yet it is Lewin who has to apologize.
Form over substance.

This is an ad from a magazine of thirty or more years ago.

Now things have changed. The moralists and the PC police are here.
Nobody should be allowed to point out how wrong certain people are, not even a (former) MIT professor. Because that's rude. It's "wrong and never works". After all, everybody is special and cannot possibly be wrong and even when they are wrong it's not important, especially if they are nice.
Nobody should be allowed to tell them to go read a book on basic electromagnetism, to get educated. "Wrong" is a bad word, "ignorant" is an insult, "educate yourself" is probably a misdemeanor, if not a felony.
This is where we're at:

And this leaves us stuck with a lot of ignorant nice special people who are just 'alternatively right'.
We are not supposed to tell them to stop wasting everybody's time by spreading ignorance and go study basic physics. We are supposed to school them from kindergarten up, step by step, repeating the same things over and over every time they reset to factory settings. [note 1]

And the kindergarten stuff, sadly, is not sarchasm. When I posted this picture...

What a Kirchhoffian does not get

...I thought I had reduced the problem to its miminum terms: a disk is not an annulus, a simply connected set is not a multiple connected set. But I was wrong, that is too complex and confusing: what Kirchhoffians fail to grasp is the concept itself of "inside" and "outside". So I should have posted this picture instead

Now, to strengthen the concept and avoiding confusion due to the fact that above 'inside' is associated with two elements, while outside only has one (of the same category), here's another example.

Inside.
Outside.
They are different.

The key is that if the (net) varying magnetic field happens to be inside your circuit path is one thing, but if it happens to be outside, it's a different thing. You can see that with meshes, with Faraday in integral form, with Faraday in differential form, and everything checks beautifully. But this simple concept is simply ignored.
30 pages are not enough. Not even 30 thousand might suffice. But not for the reason you think:

Quote from: EEVBlog
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.

Sorry Dave, but this is not because the concept of path-dependent voltage is some esoteric theoretical fundamental shit like QED, virtual quarks in an alternate universe or the subliminated state of unobtanium. This is 'fundamental' only in the sense of 'basic', 'elementary', 'first year' physics. Once you understand that voltage is path dependent when there is a varying magnetic field inside your circuit, you do not need probing to know that there have to be different voltages across the two resistors.

Provided someone taught you the difference between "inside" and "outside" and you managed to retain the concept.[note 1, again]

If anything, this concept is so basic that, being taught in first or second year classes, many people simply forgot about it (relapse into illiteracy is a real thing, I experience it everyday with the English language) and when someone point out it is so basic that they should grab a first year physics book to refresh basic notions, they refuse to do it, because they think they know better and you are just insulting them (or because... see the conclusion of post 3 of 3).

[note 1] The retaining ability alone looks more and more like a superpower.
Look at how the -L di/dt term creeped up in a recent post. There were pages and pages of discussion regarding how the concept of inductance is defined for lumped components that are part of a circuit inside which there are no varying magnetic fields with the integral of the total electric field broken down into pieces to show why it has to be that way. But it is as if they never existed (so, what's the point of leaving my posts here? They just waste server space, and energy for their retrieval). All the Kirchhoffian sees is: there is something that resembles a coil in a magnetic field, hence that's an inductance L, let's plug the formula for that somewhere in the equations and proceed from there. To hell all the prerequisites and conditions that are required to condense a complex behavior into a simple quantity L.
If you get a big enough hammer, that square peg will eventually fit into that round hole. After all, if you have used successfully for pushing all those round pegs before...

All instruments lie. Usually on the bench.

Sredni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #930 on: March 05, 2019, 07:56:55 am »
post 3 of 3

On Mehdi's video in particular

Quote from: EEVBlog
I don't think anyone doubts that Lewin is ultimately right (he is), but AFAIK he failed to address any of Electroboom's practical points.
From what I have seen, it's Lewin with his fingers in his ears repeating "KVL doesn't hold" 100 times, vs Electroboom trying to methodically evaluate the problem from a practical demonstration standpoint. From that I know who I have more respect for at the very least.

A lot of people asked why hasn't Lewin responded to Medhi's objections. But he did, well before Mehdi's video of three months ago (look at the date: one year ago)

And if you go through the various Lewin's videos on this matter,  in the comment sections you will find a single comment repeated over and over (what you would certainly call 'borderline spam'), it's the one above that is dated '3 months ago'.

multiple comment by lewin, post mehdi's video

Guess what: he's not repeating it because he's having a bad senescence episode. He's repeating it because, basically, that's all there is to it.

Quote
Lewin: In the case of an induced EMF the potentials in a circuit are no longer determined, they depend on the path

Should he go on indefinitely to answer such basic stuff? I can understand why he stopped doing it.

Quote from: EEVBlog
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",

Look at the most recent video by Mehdi, "The conclusion"

He tries to put the all thing down to the OLD KVL vs NEW KVL problem. But even there he fails to see the crucial point.

Mehdi@8:08 "KVL says that the sum of all voltages in a loop must be zero".

So, there you have it. He's saying this looking at the Romer-Lewin ring.
He is assuming you can apply KVL  to a varying magnetic field region, or that you can have single valued voltages inside the loop so that their sum has a meaning without further specification. This is the problem.
You can have such single valued voltages only if there are no varying magnetic fields enclosed by the loop.
This is the part that Kirchhoffians do not understand. They seem to believe that when people tell them that they should not have dB/dt within the circuit's premises, it is implied there has to be no dB/dt at all, anywhere. Sorry guys, but if you had read some serious book on EM you would know that NEW KVL works with varying magnetic fields inside the components BUT still require that there be NO VARYING magnetic field INSIDE the CIRCUIT PATH.

Like other Kirchhoffians, Mehdi is struggling with the concepts of "inside" and "outside".

To pretend that Lewin is mistakenly using the old (pre-Faraday) version of KVL, where there are no varying magnetic fields at all anywhere, is intellectually dishonest. And since a large chunk of Mehdi's audience appears - from the comments - to have bought that line of defense, I wouldn't be so harsh in dismissing the qualifier of "dim-witted" attributed to them by bsfeechannel.

Also, Mehdi should pay attention to what E is. Is it the coulombian field, or is it the total field, sum of the coloumbian and induced parts? It appears to me that Belcher tried to tell him, but he seems not to have understood it.

I could go on with little things like these (that might happen to be just slips of the tongue):

Mehdi@10:22 "each meter reads the voltage across the resistor on their side"

not quite, the meters read a voltage that is very close to the voltage of the resistor on their side. But that's nitpicking.

Mehdi@11:33 "if the field is going through the page in that way, the induced current is in this way"

nope, it's not how the field is directed that counts, it's how it is varying. You can have opposite currents with the field always entering the page, depending on whether the field is increasing or decreasing. Not nitipicking, this is an important distinction, but it's a forgivable slip in a long video.

Mehdi@11:40 "we can split this integral..."

does Mehdi realize that in addition to the endpoints a and b he has to specify the path, as well? It might seem so, but I am not sure at all because of what he says later on.

Or I can get to the real beef that comes at minute 13 or something - when Mehdi mentions Feynman. He says he understood how the voltage across the inductor can be nonzero even if the path integral across the conductor it is made of is basically zero and shows the circuit with the gamma line (fig. 22-9)

Mehdi@13:51 "and doing so the book shows that the sum of all voltages in the loop is zero and KVL holds"

From the smile of satisfaction (and the triumphant music) I infer that he believes this is proving him right. And he goes on saying

Mehdi@13:58 "So professor Belcher also concluded that doctor Feynman himself and I have the same definition of voltage and that KVL holds in all cases"

All of this is a load of bullshit. Why? Because in Feynman's book it is clearly stated that THERE HAS TO BE NO VARYING MAGNETIC FIELD INSIDE THE GAMMA LINE.

http://www.feynmanlectures.caltech.edu/II_22.html

A condition that is not satisfied by the Romer-Lewin ring.

Inside. Outside. Different things.

KVL does not hold in all cases (yes, Medhi actually said that KVL holds in all cases) and neither Feynman nor Belcher have ever written that it does.
And yet Mehdi put that load of bullshit into their mouths and his audience bought it. Hook, line and sink.

Oh, and then he goes on for minutes showing off how KVL is so useful, completely omitting the fact that its usefulness is subordinated to its applicability. Dude, learn to use your tools, but most importantly learn when you can use them.
It looks like he's throwing smoke in the eyes of his audience as if to say: look how useful this thing is! Can you believe Lewin wanted to do away with it?

Quote
Professor X is saying I cannot walk on water. But here I am, walking on grass. See? I can even jump and run. Walking is very useful, a lot of runners walk and run every day. Professor Y and Z agree with me.
QED.

This is intellectual dishonesty.
If you do not see this and believe that I have just demonstrated professor X is wrong, well, you are dimwitted.
(Yes, I can see beanflying bleeding from the eyes and bursting into flames)

<pause while someone grabs a fire extinguisher and put off the fire>

And I know it never ends. You have to go till the end of the video, otherwise the dimwitted audience will take that omission as running away from the real explanation that surely will been given from that point onwards. So...

At 14:58 Mehdi even reads Feynman

Mehdi@14:58 "A separation is made between what happens inside and what happens outside"

Inside.
Outside.
So they really are different things.
Does Mehdi know how important is to distinguish between them?

Mehdi@15:02 "This is important to know because..."

It seems so! But then:

"...even if the field is not contained and leaks outside, we still have an inductor and [??defined??] voltages are everywhere and KVL holds"

Oh, no, it seems he doesn't. But wait:

Mehdi@15:10 "But this creates huge complexities in our calculation because now the leaking field affects all the components and wires in the circuit that we have to take into account."

Oh, he seems to get it, but wait again...

Mehdi@15:20 "... which is almost impossible because now there are so many new variables introduced that we might easily overlook".

Actually it's more that you no longer have a single-valued voltage in your circuit (as Lewin tried to tell him) and you need to resort to fields and compute path integral along specified paths. (Feynman says it's almost imposibile when you have hundreds of components, but it can still be done rather easily with the Romer Lewin ring - as a matter of fact, a little bit of vector calculus will show why the voltage along the circuit happens to be only at the resistors)
Did he get it? Let's see:

Mehdi@15:26 "Our simple loop and probes was the easiest example of uncontained field. The field closes around the entire circuit and affects everything. Every piece of wire and even the resistor itself  become and inductor and the secondary of a transformer".

So, it's definitive. He does not get it.
He does not get it that in order to model the components as inductors and secondaries of transformers you need to satisfy the prerequisites for the application of lumped circuit theory. That is, you need for your CIRCUIT PATH to have NO VARYING MAGNETIC FIELDS INSIDE OF IT.

Inside.
Outside.
Different things.

Q.E.D.
(sounds pompous, doesn't it?)

P.S.
what remains regards avoiding the leakage unwanted flux on the outside of the circuit (he seems to still be thinking that the multiple valued voltage can be explained with bad probing) and him still falling into the trap of believing there is a voltage developed along the conductor

Mehdi@17:50 "every piece of wire is an inductor. If we have a voltage V across the main loop we would also have half a V induced on equal length of prove wire exposed to the same magnetic field"

fig a 17:54

"A more proper scientist like Romer would say..."

Yes he would say something different because the voltage across an open wire depends on the path along which it is evaluated. And if you go along the wire as Mehdi shows with the movement of his marker (and lack of specification of any other path), it is essentially zero.
To say that there is v/2 on the half arc is the same as saying that there is a build-up in voltage along the coil of a transformer, Mabilde-like. And that is wrong.
But no, the concept of wrong is not allowed.

"it is not wrong, but it's a bit misleading"

Of course, wrong is a bad word. How could anything be wrong? Just like the energy flow guy from Science Asylum ("Energy doesn't flow the way you think", youtbue video C7tQJ42nGno) who is propagating the concept that the electric field inside the copper wires is much stronger than immediately outside, where according to him it is parallel to the wires. In the pinned comment he says "it's not a mistake, it's an educational choice".
Despite the shitload of papers some viewers have posted to prove how wrong he is.

Someone here mentioned the Dunning-Kruger effect. Yes, I guess it plays a role in all these matters. I only wonder where is the threshold: one hundred thousand? five hundred thousand? one million subscriptions?

As I said before, scientific populism is going to be a big problem a few yeas ahead.
Flatearthers, moonhoaxers, antivax and climate change deniers are just the tip of the iceberg.

All instruments lie. Usually on the bench.

Sredni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #931 on: March 05, 2019, 08:01:32 am »
Post 1 of 3

On the Moderation

Quote from: bsfeechannel
However we need to express our appreciation for Simon's work. I've been a moderator before. It is one of the most ungrateful tasks, let me tell you.

I'm sorry but there's no room for appreciation for sloppy work and for the incongruent justification he gave for my ban. I could go into details, but it is clear from what he did and wrote that feedback is something to print on T-shirts and that's it. So, why waste time? He probably does not even know how his messages are rendered by browsers outside the one he uses (or that when one is banned there is no way to send PMs).

But I want to add something to explain why I deleted the technical part of my last posts and, since the thread is now dead, to address what I see as the real problem in the Lewin-Mehdi discussion. I won't get into the physics, it's not worth the time spent.

Quote from: Berni
I also don't understand what Sredni was trying to accomplish by deleting content from his posts. Basically vandalizing his own work to make it harder for someone else to follow the tread.

Quote from: EEVBlog
Yep, I don't get it either, all that hard work gone, but we've seen this before on the forum and it usually doesn't end well unfortunately. I hope that doesn't end up being the case here.

What do you expect? Me going Turbo and try to kill princess Vanellope?
Nah, I simply decided not to contribute to this blog anymore than it is necessary to get my potential future questions answered. You had someone who could provide content (and believe me, I had a lot more material to share), now you have a leech.

I removed only the technical parts from my previous posts and left all that remained because I still had the curiosity to know what earned me a ban (apart from Simon to be a precog, as postulated by ogden), but it's clear that that curiosity is going to remain unanswered. Since I did not see anything in particular, I deduced that what irked the guy who reported 'the topic was getting heated' was the technical part. So I removed it. Yeah, a waste of work and time, much in the same way the time and work I had put in my last post (on when it is desirable to contain the whole field) was wasted due to the ban.

If the people who manage the site don't care, why should I?

Technically this was post 1 of 3, but I posted it as last because, you know, when it is not clear why you guys ban people, one never knows when their 'hard work' can go wasted.

All instruments lie. Usually on the bench.

Claudiovpm

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #932 on: March 05, 2019, 08:33:29 pm »

HuronKing

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #933 on: March 06, 2019, 12:16:28 am »
I've benefited from your contributions Sredni. I've been silently following the conversation here (I just registered so I could comment) but I actively participated in the Youtube conversations on both EB's and Lewin's channels. I was the person who reminded Lewin about the Romer paper which he mentioned in one of his response videos (he credited me by my YT moniker).

As a matter of fact I've used this very discussion as a teaching example in my lab classes on electric motors and power electronics. I've made it a point to remind the graduating seniors of electrical engineering that Maxwell's Equations are the Laws of Classical Electrodynamics and have used the Romer-Lewin Ring paper and demonstration as a pointer to that fact.

It's a good thing our technological progress is governed by hard mathematics and experiment, otherwise we would still believe that objects of different masses fall at the same rate, because believing otherwise violates our 'intuition.'

By the way, it's easy to demonstrate that fact even without a vacuum chamber. Put a tiny sheet of paper on top of a textbook and drop them both.

Anyways, Lewin was/is correct and has been all along.

bsfeechannel

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #934 on: March 09, 2019, 07:34:36 pm »
I've benefited from your contributions Sredni. I've been silently following the conversation here (I just registered so I could comment) but I actively participated in the Youtube conversations on both EB's and Lewin's channels. I was the person who reminded Lewin about the Romer paper which he mentioned in one of his response videos (he credited me by my YT moniker).

Welcome to the forum. We need more people like you and Sredni around here to help us disentangle those fundamental concepts.

Quote
As a matter of fact I've used this very discussion as a teaching example in my lab classes on electric motors and power electronics. I've made it a point to remind the graduating seniors of electrical engineering that Maxwell's Equations are the Laws of Classical Electrodynamics and have used the Romer-Lewin Ring paper and demonstration as a pointer to that fact.

That's why we keep the discussion going on, because of the silent majority that really benefits from it. Our "opponents" help us reveal what exactly is the difficult point in the understanding.

Quote
It's a good thing our technological progress is governed by hard mathematics and experiment, otherwise we would still believe that objects of different masses fall at the same rate, because believing otherwise violates our 'intuition.'

By the way, it's easy to demonstrate that fact even without a vacuum chamber. Put a tiny sheet of paper on top of a textbook and drop them both.

There has been good and encouraging threads on this forum about the importance of math and fundamental physics for engineers. Coming from a practical electronics background, I felt kinda overwhelmed by the amount of math and theory we had at college, but I learned to appreciate it along the years. It really makes a difference knowing why, not only how.

Knowing how gets the job done. Knowing why makes you the boss.

Quote
Anyways, Lewin was/is correct and has been all along.

One thing that intrigued me was why Mehdi had this obsession about Lewin. Why would he and Mabilde try to discredit him? They say they "respect" him, but at the same time try to convey the idea that he essentially has no clue about circuits.

That obviously makes no sense at all. He was teaching Maxwell's equations, which contain the most fundamental circuital laws: Faraday's and Ampere's laws. So Lewin understands everything about circuits.

If you want to really understand about circuits, look no further: study electromagnetism.

Another thing that intrigued me was why Mehdi was not honest about his own perplexity. And finally, why no one in his audience managed to point out the contradictions in his rhetoric.

Then two things came to my mind. First it was this message, where Dave said:

Quote
The TS100 has a massive installed base of fanboys that have been pestering me for a year now to basically validate their purchase for them.

The other thing was this video titled "Why can't you go faster than light?" published in 2017 by Fermilab. There Dr. Don Lincoln, the host, addresses the following problem:

Quote
While each of us have developed an intuition about how the world works, it's very important to remember that this intuition only applies to a very limited set of conditions. For instance, there's absolutely no reason to expect that matter will act the same in the center of the sun as it does here on Earth on a bright and sunny day. However, that last statement is hard for some people to accept and, judging by my email inbox, the extreme realm that causes people the most difficulty is what happens when things are going super-fast.

I like this shot of Dr. Lincoln's mock-up inbox taken @00:54 while he gives his talk.

Pay attention to the name of the fake senders and the subject of their messages.

I connected the dots and concluded that the motivation behind Mabilde's and Mehdi's videos was to get Lewin to validate their intuition. An intuition that only applies to a very limited set of conditions. Lewin refused that role and took the heat. Dr. Licoln did the same with his video, albeit more successfully.

However, it's clear that this is not an isolated phenomenon: people who do not care to master the anti-intuitive character of nature feel themselves entitled to try to validate their intuition and discredit those who refuse it.

Finally, I was intrigued about how recalcitrant people are to accept the scientific truth and ditch their pseudo-scientific claims, even after we repeatedly showed that they are utterly false. Then I came across this dialog between Dave and Shahriar in this interview on The Amp Hour Podcast starting from 45:28, which sounds like a symphony, so timely it happened in relation to the current state of affairs:

Quote
Shahriar: We are at an age where information is free, right? This is pretty much the first time in human history, where you have access to the to the entire collective human knowledge in the palm of your hand. This is an astonishing outcome of our ingenuity, but at the same time what you also have in the palm of your hand is an unlimited set of misinformation, so what is the skill you need? Right? Thirty years ago you needed the skill to know things. Now you need the skill to know how to put things apart. That's the skill you need. So, but, are we teaching that? [...] But, if you don't teach people how to sort through information, in an information age, then things get out of control, because then you have no idea how this is going to turn out. And then we see effects of that in the world.

Dave: And people are susceptible to uh more powerful people who wanna take advantage of that fact, that people don't know how to sort out.

Shahriar: I mean it becomes so easy, right? And the issue with this is that any piece of information put on line especially in social media, social media is just, I mean, we use social media all the time, so, you know, we're bashing exactly the thing we're using, but at the same time it's such a disaster, because every piece of information that shows up, especially a person's ignorance, is just as valuable as a scientist's input, because there's no way to discern them, if you don't know how to discern them.

Dave: But it's not just that, because you can put true, you know, incontrovertible data in front of someone and they still won't believe it.

Shahriar: That's a whole other issue is that people... In order for you to change your mind about something that you fundamentally hold dear is that you have to make an emotional sacrifice because you have to abandon something you sure relied on and that can be difficult and that can be hard and more importantly you have connected with other human beings who share your point of view and now you're all of a sudden alone if you let go of that idea. [...] [P]eople build communities around information which may be false ultimately.[...]

I can't help comparing Shahriar to Mehdi. Shahriar is everything Mehdi isn't: knowledgeable, insightful, respectful of the work of scientists, open to abandon any false intuition in favor of true scientific knowledge. He doesn't need to play a clown to call the attention upon himself: he works at the Bell Labs, darn it, where every design engineer would like to be. His channel is non-for-profit because he wants to give back to the community as much as he can and because "the most wonderful thing you can do to another human being aside from loving them is teaching them" (1:14:04) . Shahriar suddenly became my own personal Jesus Christ.

So, that explains Mehdi's lying about his intuition being ratified by science. He and his audience have an enormous difficulty in accepting that their intuition is bullshit because that has an emotional cost. This is serious business especially due to Mehdi's popularity.

Shahriar and Dave are right: it doesn't help just showing the true and incontrovertible data, we need to help people discern bullshit from truth.
« Last Edit: March 09, 2019, 07:36:50 pm by bsfeechannel »

HuronKing

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #935 on: March 10, 2019, 07:31:17 pm »
Lewin actually predicted this reaction in his original lecture video with the story about the professors of physics and engineering accusing him of cheating on the demonstration years before. All he said was, "that tells you something about them... their brains couldn't handle non-conservative fields."

I will say lots of EB's audience tried to point out the contradictions to him. I was one of them. I wasn't one of his Patreon subscribers so I guess my voice might've held less weight in his private echo-chamber. This is what made me lose lots of respect for EB (and has made me unsubscribe from him). Behind his smile and faux-humble demeanor of "just asking questions" was a smugness of trying to "show Lewin his errors." Go find any of his comments to people on Reddit or those that are publicly viewable in his Patreon page about this.

He wasn't interested in learning from the professor or trying to seek a higher understanding of the phenomena. EB certainly did nothing to actually correct Lewin's supposed errors (see my remarks further below).
For example, he would've waited to complete his dialogue with Dr. Belcher before releasing a video on his channel accusing Lewin of the "bad probing" nonsense. Lewin was quite generous in this regard to direct EB to someone still actively teaching at MIT in order to answer his questions.

Or, EB would've pushed the scope of his research farther than skimming a Wikipedia article on voltage and KVL... you know, like cracking a book on Applied EM (Ulaby, Hayt, Jackson, Purcell which is available for free online, etc). Someone claiming a Masters of EE running a channel teaching people about electricity ought to have at least one lying around and some basic skill at vector calculus to understand Stokes' Theorem (also known as The Srendi Inside-Outside Theorem, lol). He would've seen the path-dependency requirement of voltage in non-conservative vector fields if Lewin's lecture wasn't thorough enough.

Or EB could've done a 2-second cursory Google search to find Romer's original paper detailing the experiment, as I did. Which would've led him to Feynman's Lectures and Feynman's EXPLICIT statements that the Lumped Model assumption only holds when time-varying magnetic fields aren't shooting through your circuit path - which isn't the case in the Romer-Lewin Ring.
I found this link below after 5 seconds of Googling:
https://courses.cit.cornell.edu/ece303/Lectures/lecture11.pdf

Like, how much preparatory research did EB actually do before essentially accusing Lewin of cheating on the experiment to millions of subscribers? I know people who seek better rigor in their research when presenting a paper to 30 other engineers at a small IEEE Conference, let alone a channel with millions of subscribers counting on well-researched information.

I was flabbergasted at the end of EB's video in which he proposes a scheme for measuring the One Ring Voltage to Rule Them All... but never performs the measurement despite having shown he has set up the apparatus to do it! It's telling to me that his original video offers no proposal of what this One Ring Voltage to Rule Them All should be. No mathematical prediction, nothing. Just an insistence on the intransigence of KVL even in time-varying magnetic fields. For someone trying to correct Lewin's errors, he didn't actually offer an alternative explanation of the phenomena being observed.
So, okay, KVL Always Hold and there is a One Ring Voltage to Rule Them All. Then show us what it is, Sauron!

There is a lot to learn from this case-study beyond just the issues with understanding non-intuitive things and hiding bad pop-pseudoscience with flashy graphics and funny editing. EB also demonstrated how NOT to research something.

So, I am grateful for your contributions Sredni and bsfeechannel. You guys have shown some very useful examples and perspectives on this phenomena (both Faraday's Law and the pseudo scientific understandings of it) I hadn't considered before. Thanks!

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jesuscf

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #936 on: April 07, 2019, 12:23:51 am »
For those of you that keep defending Dr. Lewin's 'superior' understanding of circuit theory, please take a look at its series of videos about problem #24: 'Circuit with 5 resistors':

Now, tell me what is wrong with 'his' approach at solving such a simple circuit.
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EEVblog

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #937 on: April 07, 2019, 12:57:29 am »
On the Moderation
Quote from: bsfeechannel
However we need to express our appreciation for Simon's work. I've been a moderator before. It is one of the most ungrateful tasks, let me tell you.

I'm sorry but there's no room for appreciation for sloppy work and for the incongruent justification he gave for my ban. I could go into details, but it is clear from what he did and wrote that feedback is something to print on T-shirts and that's it. So, why waste time? He probably does not even know how his messages are rendered by browsers outside the one he uses (or that when one is banned there is no way to send PMs).

But I want to add something to explain why I deleted the technical part of my last posts and, since the thread is now dead, to address what I see as the real problem in the Lewin-Mehdi discussion. I won't get into the physics, it's not worth the time spent.

Quote from: Berni
I also don't understand what Sredni was trying to accomplish by deleting content from his posts. Basically vandalizing his own work to make it harder for someone else to follow the tread.

Quote from: EEVBlog
Yep, I don't get it either, all that hard work gone, but we've seen this before on the forum and it usually doesn't end well unfortunately. I hope that doesn't end up being the case here.

What do you expect? Me going Turbo and try to kill princess Vanellope?

We have seen people start off deleting their posts and then going on to do real harm to this forum as some form of vendetta.
I'm not saying you will, just saying we have seen this too many times in the past, it happens.

Quote
Nah, I simply decided not to contribute to this blog anymore than it is necessary to get my potential future questions answered. You had someone who could provide content (and believe me, I had a lot more material to share), now you have a leech.

That's a shame. But you are the one who deleted all your posts, not us.

Quote
I removed only the technical parts from my previous posts and left all that remained because I still had the curiosity to know what earned me a ban (apart from Simon to be a precog, as postulated by ogden), but it's clear that that curiosity is going to remain unanswered. Since I did not see anything in particular, I deduced that what irked the guy who reported 'the topic was getting heated' was the technical part. So I removed it. Yeah, a waste of work and time, much in the same way the time and work I had put in my last post (on when it is desirable to contain the whole field) was wasted due to the ban.

If the people who manage the site don't care, why should I?

We do care that you removed your content, that's a real shame. But it's you who made that decision, I hope you are not accusing us of somehow forcing you to do that?

Quote
Technically this was post 1 of 3, but I posted it as last because, you know, when it is not clear why you guys ban people, one never knows when their 'hard work' can go wasted.

When people are banned their posts are NOT deleted, so no "hard work" is lost, the content still remains for others to enjoy, learn from and discuss. You and you alone decided to delete all your posts and your hard work.
« Last Edit: April 07, 2019, 12:59:25 am by EEVblog »

rfeecs

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #938 on: April 08, 2019, 12:57:31 am »
For those of you that keep defending Dr. Lewin's 'superior' understanding of circuit theory, please take a look at its series of videos about problem #24: 'Circuit with 5 resistors':

...

Now, tell me what is wrong with 'his' approach at solving such a simple circuit.

He presented a correct solution in the first 5 minutes of the second video.  He used mesh analysis with three loops.  (Which of course involves KVL).

Then he mistakenly thought he had a very clever way of doing it with two loops.  He got the right answer but had wrong assumptions and drew some wrong conclusions.  So all the rest of the videos are his admitting he made a mistake and explaining what he did wrong.

So he made a mistake, and then corrected it.  Not a great reason for bashing him.

jesuscf

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #939 on: April 08, 2019, 02:50:10 am »
For those of you that keep defending Dr. Lewin's 'superior' understanding of circuit theory, please take a look at its series of videos about problem #24: 'Circuit with 5 resistors':

...

Now, tell me what is wrong with 'his' approach at solving such a simple circuit.

He presented a correct solution in the first 5 minutes of the second video.  He used mesh analysis with three loops.  (Which of course involves KVL).

Then he mistakenly thought he had a very clever way of doing it with two loops.  He got the right answer but had wrong assumptions and drew some wrong conclusions.  So all the rest of the videos are his admitting he made a mistake and explaining what he did wrong.

So he made a mistake, and then corrected it.  Not a great reason for bashing him.

Nope.  The issue is more fundamental than that.
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Berni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #940 on: April 08, 2019, 05:10:40 am »
Yeah this is exactly what Kirchhoffs circuit laws are meant to be used for. Follow them correctly and they always work in ideal circuit meshes.

Tho me personally i would solve the circuit by using Thevenins theorem to create voltage dividers out of the pairs of resistors across the battery. It gets to the result by only plugging a few numbers into ohms law rather than a hefty system of equations.

Tho you will find Thenenins theorem being "for the birds" too if you suddenly start mixing it with Maxwell carelessly.

rfeecs

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #941 on: April 08, 2019, 04:04:05 pm »
Nope.  The issue is more fundamental than that.

Care to explain?

jesuscf

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #942 on: April 08, 2019, 07:13:35 pm »
Nope.  The issue is more fundamental than that.

Care to explain?

Dr. Lewin is using mesh analysis and making a big fuzz about 'his' solution that results in only two equations and two unknowns.  This compared to the 'brute force' method that yields three equations and three unknowns.  What Dr. Lewin doesn't seem to know is that if he uses nodal analysis he'll end up with the minimum number possible of equations and unknowns.  Always.  The difference in efficiency and simplicity is so significant, that mesh analysis should be only used in the simplest of circuits; those with only one or two meshes.  Unfortunately it seems to me that mesh analysis is the only method taught in physics courses.

For example, consider the problem Dr. Lewin is proposing, and solve it using nodal analysis:

Where I added anything in red.  The problem is to compute 'I' and 'i'.  I start by defining the unknown node voltages V1 and V2.  Also, I picked a reference node, in this case the negative terminal of the voltage source.  Now, apply KCL at nodes with voltages V1 and V2:

$\left\{ {\begin{array}{*{20}c} {i_a - i - i_b = 0} \\ {i_c + i - i_d = 0} \\ \end{array}} \right.$

The currents can be computed from the node voltages:

$\left\{ {\begin{array}{*{20}c} {\frac{{V - V_1 }}{R} - \frac{{V_1 - V_2 }}{R} - \frac{{V_1 }}{{2R}} = 0} \\ {\frac{{V - V_2 }}{{2R}} + \frac{{V_1 - V_2 }}{R} - \frac{{V_2 }}{R} = 0} \\ \end{array}} \right.$

Simplifying:

$\left\{ {\begin{array}{*{20}c} {5V_1 - 2V_2 - 2V = 0} \\ {2V_1 - 5V_2 + V = 0} \\ \end{array}} \right.$

From which we find both V1 and V2:

$\begin{array}{l} V_1 = \frac{4}{7}V \\ V_2 = \frac{3}{7}V \\ \end{array}$

With the node voltages it is a piece of cake to compute the required currents:

$i = \frac{{V_1 - V_2 }}{R} = \left( {\frac{4}{7} - \frac{3}{7}} \right)\frac{V}{R} = \frac{1}{7}\frac{V}{R}$

$I = \frac{{V_2 }}{R} + \frac{{V_1 }}{{2R}} = \left( {\frac{3}{7} + \frac{4}{{2 \times 7}}} \right)\frac{V}{R} = \frac{5}{7}\frac{V}{R}$

It is also possible to quickly obtain the nodal equations by inspection, but I leave up to here.
« Last Edit: April 08, 2019, 09:00:05 pm by jesuscf »
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rfeecs

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #943 on: April 08, 2019, 10:38:16 pm »
Nope.  The issue is more fundamental than that.

Care to explain?

Dr. Lewin is using mesh analysis and making a big fuzz about 'his' solution that results in only two equations and two unknowns.  This compared to the 'brute force' method that yields three equations and three unknowns.  What Dr. Lewin doesn't seem to know is that if he uses nodal analysis he'll end up with the minimum number possible of equations and unknowns.  Always.  The difference in efficiency and simplicity is so significant, that mesh analysis should be only used in the simplest of circuits; those with only one or two meshes.  Unfortunately it seems to me that mesh analysis is the only method taught in physics courses.

I agree your nodal solution is a "super" solution with only two equations and two unknowns.  Dr. Lewin definitely screwed that one up.

There are other ways to solve it as well, like Berni mentioned Thevenin equivalents.  There is also Delta to Y conversion.  I'm sure there are others that might be taught in circuit analysis classes but not in first year physics classes.

I'm not sure nodal analysis always results in the fewest equations and unknowns.  For example, this circuit I think has 9 meshes, but 11 nodes, not counting the three corner nodes:

jesuscf

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #944 on: April 09, 2019, 12:43:37 am »

I'm not sure nodal analysis always results in the fewest equations and unknowns.  For example, this circuit I think has 9 meshes, but 11 nodes, not counting the three corner nodes:

Excellent point!  I should had been more precise by indicating that the unknowns are actual branch currents and/or node voltages.  With the circuit shown and 9 meshes we can calculate 9 mesh currents, but many of those 9 mesh currents are not actual branch currents.  Therefore extra equations are needed if we want to compute them.  Actually, we can probably get away with fewer meshes/loops, but still need extra equations to compute the branch currents.  Here lies the problem with mesh analysis: what meshes should we pick?  With nodal analysis there is no guessing.  With 11 nodes we get 11 equations and 11 unknowns; even better, the unknowns are the nodal voltages.
« Last Edit: April 10, 2019, 06:26:34 pm by jesuscf »
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EEVblog

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #945 on: April 09, 2019, 12:55:09 am »
Unfortunately it seems to me that mesh analysis is the only method taught in physics courses.

EEVuniversity teaches all three

Berni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #946 on: April 09, 2019, 05:24:40 am »
Yeah there are indeed many ways to tackle solving this.

Just that the mesh analysis with loops requires the least knowledge to apply. The same exact thing is done for every section of the circuit and and all of the currents pop out as a result.Tho as the circuit gets bigger and more complex the system of equations can start getting unreasonably large for calculating by hand (I always kept a graphic calculator around for solving these automagicaly).

jesuscf

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #947 on: April 09, 2019, 06:24:44 am »
I was planing on getting the equations for the sudoku circuit both using nodal analysis and mesh analysis but after the nodal analysis I am out off gas!  I see why people use computers to solve these things...

$\left\{ {\begin{array}{*{20}c} {\frac{{V - V_1 }}{{R_{11} }} - \frac{{V_1 - V_3 }}{{R_8 }} - \frac{{V_1 - V_2 }}{{R_4 + R_1 }} = 0} \\ {\frac{{V_1 - V_2 }}{{R_4 + R_1 }} - \frac{{V_2 - V_3 }}{{R_5 }} - \frac{{V_2 - V_6 }}{{R_2 }} = 0} \\ {\frac{{V_2 - V_3 }}{{R_5 }} + \frac{{V_1 - V_3 }}{{R_8 }} - \frac{{V_3 - V_7 }}{{R_9 }} - \frac{{V_3 - V_4 }}{{R_{12} }} = 0} \\ {\frac{{V - V_4 }}{{R_{15} }} + \frac{{V_3 - V_4 }}{{R_{12} }} - \frac{{V_4 - V_8 }}{{R_{16} }} - \frac{{V_4 - V_5 }}{{R_{18} }} = 0} \\ {\frac{{V_4 - V_5 }}{{R_{18} }} - \frac{{V_5 }}{{R_{21} }} - \frac{{V_5 - V_9 }}{{R_{22} }} = 0} \\ {\frac{{V_2 - V_6 }}{{R_2 }} - \frac{{V_6 - V_7 }}{{R_6 }} - \frac{{V_6 - V_{10} }}{{R_3 + R_7 }} = 0} \\ {\frac{{V_6 - V_7 }}{{R_6 }} + \frac{{V_3 - V_7 }}{{R_9 }} - \frac{{V_7 - V_{10} }}{{R_{10} }} - \frac{{V_7 - V_8 }}{{R_{13} }} = 0} \\ {\frac{{V_7 - V_8 }}{{R_{13} }} + \frac{{V_4 - V_8 }}{{R_{16} }} - \frac{{V_8 - V_{11} }}{{R_{17} }} - \frac{{V_8 - V_9 }}{{R_{19} }} = 0} \\ {\frac{{V_8 - V_9 }}{{R_{19} }} + \frac{{V_5 - V_9 }}{{R_{22} }} - \frac{{V_9 - V_{11} }}{{R_{23} + R_{20} }} = 0} \\ {\frac{{V_6 - V_{10} }}{{R_3 + R_7 }} + \frac{{V_7 - V_{10} }}{{R_{10} }} - \frac{{V_{10} - V_{11} }}{{R_{14} }} = 0} \\ {\frac{{V_{10} - V_{11} }}{{R_{14} }} + \frac{{V_8 - V_{11} }}{{R_{17} }} + \frac{{V_9 - V_{11} }}{{R_{20} + R_{23} }} - = 0} \\ \end{array}} \right.$

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jesuscf

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #948 on: April 09, 2019, 04:50:12 pm »
Yeah there are indeed many ways to tackle solving this.

Just that the mesh analysis with loops requires the least knowledge to apply. The same exact thing is done for every section of the circuit and and all of the currents pop out as a result.Tho as the circuit gets bigger and more complex the system of equations can start getting unreasonably large for calculating by hand (I always kept a graphic calculator around for solving these automagicaly).

You have a very good point there. Although nodal analysis is convenient in the sense that the 'brute force' solution is often the optimal solution from the point of view of number of equations and unknowns, it requires some knowledge/expertise to deal with certain circuit configurations.  For example, a floating voltage source may add an extra equation/unknown, where the unknown is the current through the source.  Something similar applies for voltage controlled voltage sources, current controlled current sources, current controlled voltage sources, operational amplifiers, and transformers.
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Jony130

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #949 on: April 13, 2019, 02:18:49 pm »