"Veritasium" (YT) - "The Big Misconception About Electricity" ?

[Sredni]

If KCL is dead in the loop under test, it is also reasonable to assume it is dead in the measurement loop.

No, that's not reasonable, it's absurd.  KCL doesn't 'die' here, it just gets a little behind the curve.

If it makes you feel better, you can call it that way.
My neighbor's cat was hit by a car a couple of years ago and it 'just got a little behind the curve' since then.
Sounds a lot better, I have to concede that.

It's a transitory thing

Well, yes. That's what we some people are trying to analyze: what happens in the first few nanoseconds before the perturbation that travels along the wires reaches the load.

and that is why I've repeatedly asked you about the timeframe.  What is the permittivity of the conductors in this timeframe?  How large is the measurement loop compared to the test loop?  I would have been more careful than AlphaPhoenix with the test setup, but for the timeframe he was displaying it was fine.  Or at least OK-ish.  Maybe.  KCL doesn't 'work' in the main loop for a microsecond or so due to the propagation speed and self-capacitance and probably other things.  The KCL issues in the measurement loop are going to be in the double-digit picoseconds at most.

Look at Ben Watson's simulation data for that 9cm x 2.5 cm strip (IIRC), you can see that even after 620 ps after the 'switch has closed' the currents in three different points of the loop are very different. To me that means that KCL dies gets behind the curve, and it's still de--- way behind the curve after 1.8 ns, for that tiny strip.
Maybe when you say "gets a little behind the curve" you are thinking about ordinary transmission lines with periodic excitation. Then I can understand what you mean. KCL still dies, but can be seen alive in the model with a lot of distributed components - so we can say it's alive and well and just behind the curve.
But the transient between 200ps and 820 ps in Ben's simulation is a one-off due to the pulse coming from the switch closing (even if he used something different, and we could argue about that). In the case of Derek's simulation it would happen in the time comprised between t=0 (or t=d/c, if you wish, where d is the distance switch-load) and t=2L/c (where L is the length of each 'arm' of the line - I am neglecting the velocity factor for simplicity.
Also note that in the two transmission line model, the 60ps delay between the closing of the switch and first current in the load would not be visible.

[Cerebus]

What is the permittivity of the conductors in this timeframe?

You might want to think about that question for a second. In particular about the words 'permittivity' and 'conductor'. Hint: one working definition of a conductor would be that electric charges can freely move about in it.

I think I can see why there are a lot of people going around in circles here...

[adx]

I'm at a loss to describe my feelings on KCL, or even what it is. Fortunately I don't remember. It's probably at the core of simulator technology, in addition to matrices. Something to do with things adding up to zero, which sounds awfully like circuit analysis in model land. The type of circuits we draw with long lines representing zero length connections.

We then transform those to real connections with long lines, which may be completely unrelated to the lines on the circuit diagram. I'm sure there will be lay people not reading these forums who think we think they are intended to be the same. Analysing a schematic and analysing a PCB layout are different things. Sure, most circuits will work the same if the copper is touching in the right places (at least until production is well underway...), but I don't think anyone here for a moment would say they are the same?

I'm guessing it would be possible to add parasitics (inductors, capacitors, transformers, transmission lines and antennae and all the modelled relations) as circuit components, until all significant physical effects are modelled at least half decently - then KCL would hold. But that fundamentally contradicts the notion of circuit design, being to imagine up some solution to some functional desire, prior to throwing it all at the PCB designer.

[Cerebus]

I'm at a loss to describe my feelings on KCL, or even what it is. Fortunately I don't remember. It's probably at the core of simulator technology, in addition to matrices. Something to do with things adding up to zero, which sounds awfully like circuit analysis in model land. The type of circuits we draw with long lines representing zero length connections.

- Speechless -

[bsfeechannel]

KCL continues to hold for practically every daily use it's put to by every practicing engineer everywhere.

Dave, I love you, your channel, your blog, your forum, and I'm grateful for you being an inspiration for countless people to pursue a career in engineering. You're even the inspiration behind the name of my channel.

But someone has to say this: your understanding of electricity is incomplete. Even for a "practicing" engineer.

[bdunham7]

You might want to think about that question for a second. In particular about the words 'permittivity' and 'conductor'. Hint: one working definition of a conductor would be that electric charges can freely move about in it.

I think I can see why there are a lot of people going around in circles here...

Well, you might want to examine the limitations of the traditional notion that the permittivity of a conductor is inherently infinite.

[T3sl4co1l]

KCL continues to hold for practically every daily use it's put to by every practicing engineer everywhere.

Dave, I love you, your channel, your blog, your forum, and I'm grateful for you being an inspiration for countless of people to pursue a career in engineering. You're even the inspiration behind the name of my channel.

But someone has to say this: your understanding of electricity is incomplete. Even for a "practicing" engineer.

So all those designs I've made with KL just don't work?  Should I notify my customers?  Refund my wages as clearly I've stolen from them with such shoddy work?  What legal and technical remedies would you suggest?

Tim

[bdunham7]

Well, yes. That's what we some people are trying to analyze: what happens in the first few nanoseconds before the perturbation that travels along the wires reaches the load.

Perhaps, but I think we're discussing actually measuring a physical experiment.  If you look at the setup used by AlphaPhoenix and then your concerns, there's a huge mismatch.  I don't think anyone is trying to analyze this using KCL over the whole loop.  I'm not trying to use it at all--in a previous thread I told you I'm not a KVLer, so I guess I'm not a 'KCLer' either--unless you have a simple, isolated DC circuit.  Don't pin those labels on me.  What I'm telling you is that I think the transitory issues you mention at and around the load are much more short lived than the time resolution of that oscilloscope.  So whatever else goes on in the larger  circuit, the scope is only looking at the ends of its probes.  As far as the function of the oscilloscope, I'm not sure what you are getting at regarding KCL.  The oscilloscope does not depend on some current loop from the probe tip and ground to the input amplifier nor would any sane person try to analyze a scopes operation using KCL over its entire input circuit.  And if you are trying to argue that the scope is 'wrong', well they're always wrong to some degree.  The trick is knowing how wrong they might be in a particular situation.

So saying that there might be currents in the load that don't translate to voltage at the terminals is 1) speculative 2) very short term unless you have a little EM tornado making circular currents and 3) not really significant to either Derek's original question or the physical experiment by AlphaPhoenix.

Look at Ben Watson's simulation data for that 9cm x 2.5 cm strip (IIRC), you can see that even after 620 ps after the 'switch has closed' the currents in three different points of the loop are very different. To me that means that KCL dies gets behind the curve, and it's still de--- way behind the curve after 1.8 ns, for that tiny strip.

I don't want to comment on that simulation because I haven't had time to work with Ansys HFSS yet.  But I'm not sure who brought up KCL in the first place--was it you?--and I wouldn't expect KCL to work be up to date in circuits where either propagation times in the conductors or self-capacitance of the components was a significant issue.

[bsfeechannel]

What legal and technical remedies would you suggest?

Hire a lawyer and study Maxwell's equations?

[bdunham7]

So all those designs I've made with KL just don't work?  Should I notify my customers?  Refund my wages as clearly I've stolen from them with such shoddy work?  What legal and technical remedies would you suggest?

Nothing so dramatic is needed.  For a small fee, I can draft a disclaimer for you. 

[Cerebus]

You might want to think about that question for a second. In particular about the words 'permittivity' and 'conductor'. Hint: one working definition of a conductor would be that electric charges can freely move about in it.

I think I can see why there are a lot of people going around in circles here...

Well, you might want to examine the limitations of the traditional notion that the permittivity of a conductor is inherently infinite.

I'll do that immediately after you show me a working solid copper capacitor.

[bdunham7]

I'll do that immediately after you show me a working solid copper capacitor.

OK.  Grab any chuck of copper that you have handy.  Have a close look.  That's a capacitor. 

So with that out of the way, how does the infinite permittivity of a conductor manifest itself?  And does that process take any amount of time?  If so, what can you say about the interim period?

[SiliconWizard]

KCL continues to hold for practically every daily use it's put to by every practicing engineer everywhere.

Dave, I love you, your channel, your blog, your forum, and I'm grateful for you being an inspiration for countless of people to pursue a career in engineering. You're even the inspiration behind the name of my channel.

But someone has to say this: your understanding of electricity is incomplete. Even for a "practicing" engineer.

So all those designs I've made with KL just don't work?  Should I notify my customers?  Refund my wages as clearly I've stolen from them with such shoddy work?  What legal and technical remedies would you suggest?

Well, you thought they worked, your customers thought they worked, but now you know this was just all an illusion.
Since, once we dig a bit deeper, we realize we actually know jack shit about how the universe works, we should probably just all stop doing anything, and keep discussing about it on forums.

[Cerebus]

I'll do that immediately after you show me a working solid copper capacitor.

OK.  Grab any chuck of copper that you have handy.  Have a close look.  That's a capacitor. 

So with that out of the way, how does the infinite permittivity of a conductor manifest itself?  And does that process take any amount of time?  If so, what can you say about the interim period?

Weird, the LCR meter says it's a dead short, even at DC. I thought capacitors blocked D.C.? Silly me, I clearly know nothing and am forced to bow to your deeper knowledge of this arcane electrickery thing.

[bdunham7]

Weird, the LCR meter says it's a dead short, even at DC. I thought capacitors blocked D.C.? Silly me, I clearly know nothing and am forced to bow to your deeper knowledge of this arcane electrickery thing.

Hmm, that's odd.  Either your LCR meter is on the fritz or perhaps you accidentally connected both leads?   

[TimFox]

An infinite permittivity and zero frequency conjointly give an indeterminate impedance, equivalent to 0/0.

[T3sl4co1l]

I'll do that immediately after you show me a working solid copper capacitor.

OK.  Grab any chuck of copper that you have handy.  Have a close look.  That's a capacitor. 

So with that out of the way, how does the infinite permittivity of a conductor manifest itself?  And does that process take any amount of time?  If so, what can you say about the interim period?

Metals (or certain ones, I'm not clear on what the differences are) have surface plasmon states, which gives high conductivity (high imaginary permittivity if you prefer) at lower frequencies, but a cutoff around optical frequencies, hence copper and gold look pink to yellow, and most (all?) metals look the same regardless, just shifted to different parts of the spectrum -- evidently, with none being redder than copper, the cutoff most commonly falls in the UV, where we don't see it, so they all look silvery of course.  If you had color UV sight, the periodic table would be a bit more interesting to look at.

Plasmonic states correspond to inertial effects of charge carriers, as has been brought up earlier in this thread; they're largely irrelevant in practice, because EM wave effects dominate for most frequencies and geometries.  Basically, the plasmon waves dissipate quickly with distance (100s nm), so for anything wider/thicker than this, normal absorption/reflection effects dominate, and for incident EM waves, we can use bulk properties to describe them (whether empirical or theoretically derived), i.e. conductivity, absorption spectrum, etc..  (The same effect gives the transparency of ITO coatings, or ionospheric propagation for <= SW radio.)

So, to whatever extent you want to consider such frequencies to construct a "capacitor", or care to have complex-valued capacitance -- there you have it.

Tim

[T3sl4co1l]

Weird, the LCR meter says it's a dead short, even at DC. I thought capacitors blocked D.C.? Silly me, I clearly know nothing and am forced to bow to your deeper knowledge of this arcane electrickery thing.

Clearly whoever designed the thing is a nutjob; inductors, capacitors and resistors can't even exist!..

Tim

[Cerebus]

Clearly whoever designed the thing is a nutjob;

He's not a nutjob, he's a complete and utter Wayne Kerr.

[bdunham7]

So, to whatever extent you want to consider such frequencies to construct a "capacitor", or care to have complex-valued capacitance -- there you have it.

OK, but I was really only thinking of the inherent self-capacitance of the copper object attributable to its physical dimensions.  To be fair, that's not really related to the permittivity issue in the comment that brought up capacitance, but before anyone doles out the insults perhaps reading a few posts back to understand the context might help.  Sredni is claiming that current can be flowing in the resistor without voltage appearing at the terminals and thus not detected by the oscilloscope.  I'm pointing out that any such phenomena would be short-lived and transitory--and more importantly, not within the range of signals the oscilloscope would be expected to show.

[bsfeechannel]

Well, you thought they worked, your customers thought they worked, but now you know this was just all an illusion.

Guys, you're so melodramatic.

Clearly circuit analysis doesn't work to explain how energy flows in circuits. People, including Dave, who uselessly insist in using a completely inadequate tool to explain the phenomenon, incur invariably in gross errors.

Saying that trying to acquire the missing knowledge to explain it is "faffing around the edges of physics" doesn't help.

We are engineers. When we are faced with such a challenge, we cowboy up and learn the darn thing, instead of moaning and groaning in forums that someone more knowledgeable showed that we don't know our butts from a hole in the ground.

[bdunham7]

Clearly circuit analysis doesn't work to explain how energy flows in circuits. People, including Dave, who uselessly insist in using a completely inadequate tool to explain the phenomenon, incur invariably in gross errors.

Then why do the products designed with these 'gross errors' seem to work pretty well?

We are engineers.

Are we?

[bsfeechannel]

Then why do the products designed with these 'gross errors' seem to work pretty well?

They simply don't. When Faraday discovered the magnetic induction, he proved that energy could be transferred from a source to a load WITHOUT wires connecting the source and the load, i.e., without a circuit between the two. So circuit analysis doesn't work there. Period.

You can't design a transformer with KL. No one can. Transformers are everywhere and every single one was designed without it. Including the very first: Faraday's.

We are engineers.

Are we?

I am. Are you?

[MIS42N]

I have been trying to resolve the first microsecond of experimental results obtained by AlphaPhoenix with theory. Using theory should result in an answer near 200mV across a 1k ohm resistor.

It appears what has been constructed is a very inefficient transformer. When the switch is closed, a wave of current moves along the switched wire(s) near the speed of light. The front of the wave is at 0V, the back of the wave is at +-2.5V (depending if you are looking at the wire attached to the +ve or -ve terminal of the battery). This induces a Voltage wave in the wires attached to the bulb/resistor. As far as I can find out, the Voltage induced in those wires is proportional to the shared flux. The shared flux is the flux created by the switched wire integrated from 0d to infinity minus the flux created by the switched wire integrated from 0 to a circle of radius the separation of the parallel wires. A requirement of this conclusion is the current drawn by the bulb/resistor is small compared to the current flowing in the switched wire.

This seems like a straightforward calculation, and I'm sure that in the maze of formulae I have looked at, I've seen the right one. However, mathematics is not my strong point so I am floundering. The answer to the calculation should be 200mV/5V or about 4%.

The interesting conclusion is that the 200mV is relatively independent of the resistance, if the bulb/resistor draws negligible current compared to the current in the switched wire. It is likely 200uA is negligible but I don't know. So swapping a 2.2K resistor for the 1K resistor should give a similar result, closer to 200mV than 400mV. Also interesting is skin effects etc have no bearing on the result. They will change the shape of the pulse moving in the switched wire, but for every section of switched wire there is a parallel section of wire attached to the bulb/resistor so the pulse shape is irrelevant.

I have ignored capacitance effects in this conclusion. I estimate it will change the result by less than 50%. A large amount but a ballpark figure is better than none.

Anyone able to prove/disprove this conclusion? Just needs that flux calculation.

[bdunham7]

They simply don't.

So T3sl4co1l should have a big recall after all and issue those refunds??  Perhaps you didn't comprehend.  I asked why the products designed by uninformed cretins seem to work OK despite your alleged 'gross errors' in analysis.  Are you suggesting that in fact, the products do not function as intended?

You can't design a transformer with KL. No one can. Transformers are everywhere and every single one was designed without it.

OK, has anyone here proposed designing a transformer using Kirchoff's laws?  I think that thread is long enough and pretty dead by now, no need to drag it over here.