Does Kirchhoff's Law Hold? Disagreeing with a Master

[jesuscf]

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.

Thanks Berni, I am well aware on how transmission lines are modeled and simulated.  I was being a bit sarcastic when I posted my comment, but 'unitedatoms' was right on with his reply.   By the way, the SPICE model for transmission lines is rather simple and doesn't include coupling, like the kind of coupling present in three phase power lines (or at least it didn't a few years back).   But according to Dr. Lewin and his supporters the laws of Circuit Theory will not apply to an arrangement of wires like that.  Gladly, electrical engineers, despite their 'ignorance of Maxwell equations and laws of physics in general', had managed to model power transmission lines with great detail and use them in circuit simulators like EMTP (Electromagnetic's Transient Program).

 

[unitedatoms]

circuit simulators like EMTP (Electromagnetic's Transient Program).

What they do with magnetism in EMTP? Is EMTP sircuit based or space based ? (Circuit vs space like in Spice vs Autocad 3D). I heard of mechanical modeling approach Finite Elements Modeling, is it somehow similar to spice in mechanics.

What if someone modelled free space and metal surfaces as net lump components, then you can Spice model RF shapes of any kind. Dont know if is possible.

[Berni]

Well lump modeling is used quite a bit in RF too.

The EM simulations of distributed element filters on PCBs or 3D filter structures can get very slow. So often the results of those simulations are converted into a lumped equivalent circuit that can then be used to run simulations quickly in efficiently with tools like SPICE while still behaving accurately.

Alternatively given that you already have a physical component and want to include it into a simulator then you typically hook it up to a network analyzer and measure all of its S parameters over the frequency range of interest. This data can then be used in a simulation model or calculated into a equivalent circuit of the component.

Tho these sorts of equivalent circuits can become quite a bit mess of resistors inductors and capacitors and very few nodes in that cirucit have any actual meaning to the real life cirucit. Most voltages and currents in these big complex lump models are just partial math results of something, its only the voltage across the terminals of the whole black box is the one that actually matches a real voltage in the real cirucit.

For example here is the lumped model for a Ethernet transformer made by TDK:


This model was likely constructed from a large number of network analyzer measurements of the component, but will give very accurate behavior in a simulation to give you accurate imperfect coupling of the coils and accurate crosstalk between terminals. All while being simulated in under a second inside SPICE as opposed to being simulated for hours in a EM simulator.

Its all about engineers being efficient with there time because they have to deal with things called deadlines. Not because they wouldn't care about our old friend Maxwell, they do care, but will take a shortcut if the shortcut gives results that are just as good.

[ogden]

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.

Oh, you think that transformer (inductor with two windings) is generator? 

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.

Perpetum mobile formula of voltage drop on loads that does not include voltage source (EMF) is truly yours. Do not disgrace Kirchoff, please.

[edit] Image of "your formula" attached. You wrote I1*R1+I2*R2=0V

[bsfeechannel]

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

Mehdi and everyone that advocates that knowledge of the Maxwell's equations can be replaced by the "much simpler" Kirchhoff's equations.

This thread has proved that if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.

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.

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"

Fair enough. I'm here because of your invitation to "anyone involved in electronics design" and because "This is where everyone hangs out and rants and chats about whatever electronics topics that don't fit into the other more specific categories on this forum."

So, here I am ranting like crazy about what I find to be wrong with the world when it comes to electronics. If I don't win friends or influence people (I have the book), at least I hope someone can learn something with it.

[unitedatoms]

@beefefees
You said you wrote the book ? What was the subject? I did not follow the drama, but it looks for me like the discussion about pedagogy. Not the scientific matters. Please do not be discouraged. The only problem I have observed was that there is good and bad way to deliver the knowledge. Quality of explanation matters. Students shall not be made confused.

I will try to fix this with my little essay:

Once upon a time there in a little hole in a ground there was an Ohm. Nearby in a village lived his fellow neighbors
Volt, Ampere, Siemens, Coulomb and Second.
Children we're named Henry and Farad.
Everyone was happy, and that time we all remember as the time of zero's Planks Epoch. That was a Kirghoffs Universe. The village was ruled by a couple of Zero and Infinity, and their single child was named One.
However one day the the One said I want a sibling, and if you will not give me a sibling named Imaginary One!
Thus was born the Imaginary One. And things turn Complex. Everyone was suspecting that real father was Second. And it was only a beginning.
Soon the epoch ended, because Second was feeling insecure and sneaked into other village and became friend to evil neighbours.
Nobody was expecting the change, but change happened. An army of evil intruders attacked the village. They turned everything
Into fragments, and ever since the the things were apart. Newcomers named Meter and Kilogramm were were the eveliest of all. They
created Space, and all 3 directions to confuse the innocent villagers. They even evicted the innocents and forced them live in Fields.
Fields were ruled by Space, the evil child of Meter and Kilogramm. And that was the start of second Plank's Epoch.

The poor villagers had no choice, but to tp follow new rules. They we gathering crops using Differentials and the produce was
Stocked in large towers named Integrals. Second was promoted to be in charge of accounting and bookkeeping.
She gathered produce and reported to Joule. Joule was old neutral neighbor, but he took an advantage of all the politics.

One day Joule became enamored with Second, and they got achild named Watt. Watt Wass grew up as unremarcable fellow.
All he was caring about was efficiency, typical MBA major kind. However he was decent enough to stay away from Weber, Tesla and alike.
What Weber and Tesla did, is they built one round fence around the village. The Wall. Weber and Tesla wanted to keep
The crop safe from elements. This wall caused so may conflicting feels in a village.
However Volt was most encouraged by wall, and he volunteered to patrol it. Second supported Volt in his intitatve
and she pushed the village comitee to add Ampere and Ohm to the patrolling schedule. Weber and Tesla silently celebrated.

The story to (be unlikely) continue... Sorry too much red wine this Sunday

[Berni]

Don't think i learned much from that, but i did find the story pretty amusing, it actually fits together rather well.

[bsfeechannel]

Well lump modeling is used quite a bit in RF too.

The EM simulations of distributed element filters on PCBs or 3D filter structures can get very slow. So often the results of those simulations are converted into a lumped equivalent circuit that can then be used to run simulations quickly in efficiently with tools like SPICE while still behaving accurately.

Of course we can lump model RF elements. Otherwise you couldn't replace an antenna with a signal generator to test your receiver in the lab. You can treat propagation through the air as a big attenuator if you have a direct line of sight and no obstacle in the Fresnel zone, etc., etc. etc People who design radios do that all the time in the lab.

What is necessary to understand is when this trick fails. And it fails because you're not aware that you are making implicit assumptions when you lump model a circuit. I said this I guess three months ago or more.

Tho these sorts of equivalent circuits can become quite a bit mess of resistors inductors and capacitors and very few nodes in that cirucit have any actual meaning to the real life cirucit.

They do have an actual meaning. They are approximations. There are in fact capacitances between the wires and between the windings. The wires are really resistive. The leakage inductance is really an inductance that is coupled to the no other winding. Part of the energy is really dissipated as heat due to eddy currents and hysteresis.

They are not palpable but can be measured, as your picture shows.

Most voltages and currents in these big complex lump models are just partial math results of something, its only the voltage across the terminals of the whole black box is the one that actually matches a real voltage in the real cirucit.

If I give you a black box with two terminals hanging out and you perform the following test, you'll be easily able to build yourself a gadget that reproduces the exact effect with lumped components.



But if I give you another black box where you cannot determine exactly what voltage and what current it delivers it will be impossible to build it with lumped components.



I can obviously restrict how to take the voltage of this crazy black box and then I can try to lump model it. But hey, look what I'm doing, I'm assuming something: that the voltage can only be taken in a certain way.



Look how the technique can be confused with the phenomenon. This limits the understanding of a lot of circuits. Including some very ubiquitous circuits that you have around you.

Its all about engineers being efficient with there time because they have to deal with things called deadlines.

It's all about engineers knowing what they're doing. If you don't know what you're doing will never be efficient and will never meet any deadlines.

[EEVblog]

@beefefees
You said you wrote the book ? What was the subject? I did not follow the drama, but it looks for me like the discussion about pedagogy. Not the scientific matters. Please do not be discouraged. The only problem I have observed was that there is good and bad way to deliver the knowledge. Quality of explanation matters. Students shall not be made confused.

Completely unavoidable, confusion is inevitable with any explanation. This is why dozens of text books explain the same thing in different ways, one way "clicks" for one person but doesn't click for another.

[EEVblog]

Fair enough. I'm here because of your invitation to "anyone involved in electronics design" and because "This is where everyone hangs out and rants and chats about whatever electronics topics that don't fit into the other more specific categories on this forum."
So, here I am ranting like crazy about what I find to be wrong with the world when it comes to electronics. If I don't win friends or influence people (I have the book), at least I hope someone can learn something with it.

People are learning, and technical input like yours is always massively appreciated.
But unfortunately your approach has been somewhat abrasive (even for an engineering forum, were lack of tact and copious amounts of abrasion are commonplace) and I'm not surprised it's rubbed some people the wrong way. That was just inevitable with your approach.

[jesuscf]

This thread has proved that if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.

And this sentence proves without doubt, that bsfeechannel is not an electrical/electronics engineer or anything remotely similar.  Here you have it, the Dunning–Kruger effect at work.  It reminds me of Dr. Lewin solving his problem 34

[bsfeechannel]

Oh, you think that transformer (inductor with two windings) is generator? 

Where did you find a transformer in the circuit? There are only two wires connected to each other forming a closed figure. Exactly as Kirchhoff said it had to be.

Perpetum mobile formula of voltage drop on loads that does not include voltage source (EMF) is truly yours.

There is no voltage source in the circuit. Only two resistive wires.

Do not disgrace Kirchoff, please.

Absolutely. I'd never introduce something to Kirchhoff's formula that he has not authorized me to.

[Berni]

Its all about engineers being efficient with there time because they have to deal with things called deadlines.

It's all about engineers knowing what they're doing. If you don't know what you're doing will never be efficient and will never meet any deadlines.

Exactly. As i said the spice simulator does not do any of the thinking for you, it just munches trough the math for you. Hence why in the very first page of this long thread has my spice model that includes coupled inductors added. Observing the physical circuit i have determined that the effect of coupled inductance is a significant effect to the behavior, so i have put them in and ran the simulation to see how well it does. It behaved just like the real circuit so from that i assumed that i have captured all the most significant parasitics of the circuit. Its all about knowing your tools.

Just because there is an inductor in the spice model doesn't mean you have a physical coil of wire, or that all of this voltage appears at one point on a wire. It just tells the circuit model that this path trough the circuit experiences inductance, or in this case coupled inductance.

The black box you show up there is not really a black box as they should behave as a self contained unit that only interacts with its surrounding trough the terminals. This also means a black box works with circuit mesh analysis without making any spooky paradoxes.

[bsfeechannel]

People are learning, and technical input like yours is always massively appreciated.
But unfortunately your approach has been somewhat abrasive (even for an engineering forum, were lack of tact and copious amounts of abrasion are commonplace) and I'm not surprised it's rubbed some people the wrong way. That was just inevitable with your approach.

I'm really surprised to read that. I thought I was in my element here.

But look what I have to deal with.

This thread has proved that if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.

And this sentence proves without doubt, that bsfeechannel is not an electrical/electronics engineer or anything remotely similar.  Here you have it, the Dunning–Kruger effect at work.  It reminds me of Dr. Lewin solving his problem 34

I don't think I have said something abrasive here. How do I reply to that?

This is not the first time this guy says this about me and he did it long before I said that Mehdi shouldn't be addressed as an engineer. He is not even molested by the moderation and he'll probably be even thanked by it.

So I'm really at a loss as to what are the acceptable limits for "abrasion" in this forum. 

I like to contribute, but it is really frustrating to be mocked for that when guys like this are free to troll at will.

[EEVblog]

But look what I have to deal with.

This thread has proved that if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.

And this sentence proves without doubt, that bsfeechannel is not an electrical/electronics engineer or anything remotely similar.  Here you have it, the Dunning–Kruger effect at work.  It reminds me of Dr. Lewin solving his problem 34

I don't think I have said something abrasive here. How do I reply to that?

Simple, you don't. You ignore it and keep the talk technical.

This is not the first time this guy says this about me and he did it long before I said that Mehdi shouldn't be addressed as an engineer. He is not even molested by the moderation and he'll probably be even thanked by it.

Moderators do not actually "moderate" conversation here, we work based on reports and then we might look at the person history.
We get countless "storms in a teacup" that could be easily avoided if the person simply doesn't respond to them.

So I'm really at a loss as to what are the acceptable limits for "abrasion" in this forum. 

Start by not calling people all sorts of things and taking things too personally.
Hint, you can't be "abrasive" with just facts and technical points. But you can be with your tone and pejoratives.

IMO it's you taking this too personally that is the problem. We have seen this countless times on the forum and often it leads to rage quitting like this other poster in here seems to have done, and that's a huge shame.

I like to contribute, but it is really frustrating to be mocked for that when guys like this are free to troll at will.

You are free to ignore them, try it, it works wonders.

[jesuscf]

This thread has proved that if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.

And this sentence proves without doubt, that bsfeechannel is not an electrical/electronics engineer or anything remotely similar.  Here you have it, the Dunning–Kruger effect at work.  It reminds me of Dr. Lewin solving his problem 34

I don't think I have said something abrasive here. How do I reply to that?

This is not the first time this guy says this about me and he did it long before I said that Mehdi shouldn't be addressed as an engineer. He is not even molested by the moderation and he'll probably be even thanked by it.

So I'm really at a loss as to what are the acceptable limits for "abrasion" in this forum. 

I like to contribute, but it is really frustrating to be mocked for that when guys like this are free to troll at will.

Dear bsfeechannel I offer my most sincere apologies.  I'll very careful not to say something like this again.  One thing you can do is adding me to your "ignore list".

[beanflying]

...

I like to contribute, but it is really frustrating to be mocked for that when guys like this are free to troll at will.

So we should all just be quiet and let you go on attacking anyone you feel like on a 'personal' level? I tried to raise this politely back is December and I got Waffle back from you about 'protecting lives' to mask your attitude toward others and not to their opinions.

You 'claim' the capacity to learn but have failed miserably to manage that and comprehend the problem that others have with your so called debate and discussion methodology.

You better behave

Here's a dollar, kid. Go get yourself a better education.

or this

His video is a crime against humanity.

Who is being arrogant, after all? Mabilde and all those who recalcitrantly refuse to learn, or Lewin who dedicated an entire life to teaching?

This stubborn attitude is what is getting under our skin.

So don't fool yourself. You're not doing science a favor. If you really love science do as we all do: humbly learn.

And I won't bother repeating you @BSChannel rant of a few days ago where you used the word Liar on multiple times toward Mehdi.

Perhaps it is you who may just be getting under our skin just a little?

So, never try anymore to hide your lack of knowledge behind excuses like that. Convince yourself and others of the need to be ready to learn something new every day.

[ogden]

Oh, you think that transformer (inductor with two windings) is generator? 

Where did you find a transformer in the circuit? There are only two wires connected to each other forming a closed figure. Exactly as Kirchhoff said it had to be.

You said it is transformer:

Now let's take the open secondary of a transformer, for example, comprised of a single turn.

Perpetum mobile formula of voltage drop on loads that does not include voltage source (EMF) is truly yours.

There is no voltage source in the circuit. Only two resistive wires.

You are making your own reality on the go:

The EMF is 1V (my MOT can give me 600mV for a single turn).

[bsfeechannel]

You said it is transformer:

Now let's take the open secondary of a transformer, for example, comprised of a single turn.

I said the secondary of a transformer. The secondary of a transformer is not a transformer. But if that confuses you, instead of thinking that the varying field is being generated by the primary winding of a transformer, think of it being generated by a moving permanent magnet. It doesn't make any difference as stated in Feynman's lecture.

You are making your own reality on the go:

The EMF is 1V (my MOT can give me 600mV for a single turn).

Nope. This is a different circuit. It only has one wire and one EMF. The other one has two wires and no EMF where Kirchhoff said it should be.

[Berni]

Nope. This is a different circuit. It only has one wire and one EMF. The other one has two wires and no EMF where Kirchhoff said it should be.

Why would KVL say there is no EMF?
See this equation: http://www.feynmanlectures.caltech.edu/II_22.html#mjx-eqn-EqII2234

[bsfeechannel]

Nope. This is a different circuit. It only has one wire and one EMF. The other one has two wires and no EMF where Kirchhoff said it should be.

Why would KVL say there is no EMF?
See this equation: http://www.feynmanlectures.caltech.edu/II_22.html#mjx-eqn-EqII2234

Those equations imply some important assumptions. The wires are ideal and there's no varying magnetic fields between the terminals of the mutually coupled inductors. The terminals, i.e. the interface between Kirchhoff and Maxwell, are very important.  The word terminal occurs 81 times in this chapter. Try reading every paragraph where it is included.

To help you a bit with that, let me summarize it all with a new drawing.

[Berni]

Yep since KVL works in lumped circuits and attributes the voltage to an inductor while with Maxwell its just sums it in as a whole. Just two different ways of going about the same thing that come to the same result when used correctly.


So if you take yourself as being so knowledgeable in how to analyze circuits, have you decided yet what is the correct way to analyze the behavior of this circuit?
https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2189216/#msg2189216


I can give a trip that gain degradation on the transistor plays no role in the operation so a ideal transistor with a fixed Hfe can be used, but the parasitic capacitance in the transistor are important to the operation, all of them are stated in the datasheet for that transistor (Tho a ballpark figure for most small signal transistors is close enugh)

[rfeecs]

Yep since KVL works in lumped circuits and attributes the voltage to an inductor while with Maxwell its just sums it in as a whole. Just two different ways of going about the same thing that come to the same result when used correctly.


So if you take yourself as being so knowledgeable in how to analyze circuits, have you decided yet what is the correct way to analyze the behavior of this circuit?
https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2189216/#msg2189216


I can give a trip that gain degradation on the transistor plays no role in the operation so a ideal transistor with a fixed Hfe can be used, but the parasitic capacitance in the transistor are important to the operation, all of them are stated in the datasheet for that transistor (Tho a ballpark figure for most small signal transistors is close enugh)

I'm guessing those loops are supposed to form a transformer and the circuit is an oscillator?  So we replace the loops with a lumped transformer?  I'm trying to read your mind, maybe not successfully.

The other way to read the schematic is a wire is a zero length connection in a netlist, so that circuit doesn't do much.

How about not such an easy one:



The boxes are microstrip lines (see Dave's videos of spectrum analyzer teardowns).  Does Kirchhoff's law apply?

The traditional way to design such a filter would be to select a transfer function like Chebyshev or something that meets the requirements.  Then synthesize a lumped filter.  Then convert the lumped filter to microstrip "equivalent".  Then make it and try to tune it to get it to work.

Instead, nowadays, you run a computer program and it spits out the design.  Then you probably would do EM simulation to verify your design and layout in the enclosure.  Then you make it and try to tune it to get it to work.

So as you have said, you can make a lumped model where KVL applies.  But the real filter fundamentally isn't lumped and KVL doesn't apply to it.  So you can separate the physical three dimensional filter where you would use Maxwell's equations (in the form of a computer simulation if you value your sanity); and the abstract lumped model where you use KVL and KCL and still use a computer simulation for the same reason.

There are other structures (antennas may be one example) where it is very difficult to come up with a lumped model or there is simply no reason to try.  There you use EM (Maxwell's equations) all the way.  The end result is a 2-port or N-port black box where Kirchhoff can be applied at the ports.

[ogden]

The boxes are microstrip lines (see Dave's videos of spectrum analyzer teardowns).  Does Kirchhoff's law apply?

Obviously not. You do not apply Kirchoff's law to circuits where current in the conductor is not uniform. It is already discussed here in this thread. Dimensions of Dr.Lewin's experiment "secondary loop" is so small that any transmission line effect can be ignored for frequencies of experiment (300 Hz).

[jesuscf]

How about not such an easy one:



The boxes are microstrip lines (see Dave's videos of spectrum analyzer teardowns).  Does Kirchhoff's law apply?

What you are saying is equivalent to say: here is a silicon diode,  does Kirchhoff's law apply?  Or if you prefer: here is a transmission line, does Kirchhoff's law apply?  Don't you have to put the element in a circuit first?  Once you have a complete circuit, with every element of the circuit properly modeled, the laws of Circuits Theory apply.  That includes KVL.  In the case of this micro strip band pass filter, can you replace it with its transfer function?  If so, there are many ways of modeling the filter and include such model in the circuit.  In this case we'll have to use Maxwell's equations to derive the model (I guess, I have never done it), but that is different from using the model in a circuit.