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

[besauk]

The experiment is a bit of a red herring and doesn't really help with the main point of the film that the energy is transferred in the fields.

That is an understatement!  In his zeal to emphasize the the power flow via fields, he essentially states that the fields magically go in some directed way to a load, independent of the wire path.  Yes, there will be a tiny signal at the bulb roughly 3ns after switch closure - you'd no doubt hear a click in an AM receiver placed a meter away, but you won't see any light for at least a second.

The point being missed is that the electron flow and the fields are coupled.  While power flow can be assigned to the fields, the field propagation depends upon the conductor geometry.  The majority of the field energy propagates in close proximity along the conductor because of the interaction between the field and electrons.

[bsfeechannel]

We need to stop treating Maxwell’s equations and field theory as something to be avoided.

I'm not suggesting that we avoid or forget them, but what important advances in science or technology have been made recently using field theory?  Unless you continue on into the realm of quantum mechanics and so forth, you've long lost sight of anything all that new in the modern technological and scientific context.  The stuff you talk about is important to know and understand, but you also need to realize that as a model it, like every other model, eventually becomes either incorrect or inapplicable.  This is especially evident when we start making 'theoretical' arguments with simplified models that are physically impossible.

Are you sure about that? I mean, in the last decades devices running at frequencies in the range of GHz, the size of the palm of your hand, had become ubiquitous. Suddenly field theory became not only mainstream, but also the talk of the so called “practical” engineer.

The most widely produced device in history, 13 sextillion (13 followed by 21 zeros) of them to be precise, has the word field as part of its name. I think field theory is not a mere curiosity anymore, not even for the “practical” engineer.

[EEVblog]

He meant a transmission line, as he mentioned impedance in the video, he just didn't say it, because that gives the game away for engineers watching.
You will not ge the 1m/c answer if the lines are not 1m apart. He actually got that bit wrong and said the answer is 1/c, it's not, it's 1m/c. He doesn't even get the units analysis right, and maybe that's deliberate, because once again putting in the 1m/c instead of 1/c is giving the game away.

I think the purpose of leaving out that was just to avoid jargon to only the most salient points because most of his audience are not electrical engineers.  The fact that it is a transmission line is not necessary for the effect

The 1m distance is most certainly required if you want to get his answer of 1m/c seconds.

[ejeffrey]

The experiment is a bit of a red herring and doesn't really help with the main point of the film that the energy is transferred in the fields.

That is an understatement!  In his zeal to emphasize the the power flow via fields, he essentially states that the fields magically go in some directed way to a load, independent of the wire path.  Yes, there will be a tiny signal at the bulb roughly 3ns after switch closure - you'd no doubt hear a click in an AM receiver placed a meter away, but you won't see any light for at least a second.

The current through the lamp will be Vbatt / (2Zo + Zlamp) starting about 3 ns after switch closure and it will remain approximately the same until the rising edge reflects off the end and returns.
 Whether that generates a lot of light or not depends on the characteristics of the light, battery and the wire diameter but he was fairly clear about what he was asking.

[bdunham7]

The most widely produced device in history, 13 sextillion (13 followed by 21 zeros) of them to be precise, has the word field as part of its name. I think field theory is not a mere curiosity anymore, not even for the “practical” engineer.

I'm not saying field theory is obsolete, but rather incomplete.  And the FET is a perfect example.  It was conceived of in the early vacuum tube era when field theory was well developed but quantum mechanics was just getting started--but nobody actually was able to make them work.  Decades later, using more advanced theories and models, the FET was revived and thrived.

[besauk]

The experiment is a bit of a red herring and doesn't really help with the main point of the film that the energy is transferred in the fields.

That is an understatement!  In his zeal to emphasize the the power flow via fields, he essentially states that the fields magically go in some directed way to a load, independent of the wire path.  Yes, there will be a tiny signal at the bulb roughly 3ns after switch closure - you'd no doubt hear a click in an AM receiver placed a meter away, but you won't see any light for at least a second.

The current through the lamp will be Vbatt / (2Zo + Zlamp) starting about 3 ns after switch closure and it will remain approximately the same until the rising edge reflects off the end and returns.
 Whether that generates a lot of light or not depends on the characteristics of the light, battery and the wire diameter but he was fairly clear about what he was asking.

Respectfully disagree.  What would happen if instead we had just 10 meters of wire on each side of the bulb, and 10 meters on each side of the switch/battery, 1 meter apart, but open ended.  For the first 30 ns or so, this setup should be indistinguishable from the Veritasium setup, since nothing could propagate beyond those 10 meters in that first 30 ns.  What you have now are two dipole antennas separated by a meter.  Your claim equates to having a perfect coupling between those two antennas.  If that's the case, then we clearly have a breakthrough in wireless power transmission!

[bdunham7]

The current through the lamp will be Vbatt / (2Zo + Zlamp) starting about 3 ns after switch closure and it will remain approximately the same until the rising edge reflects off the end and returns.
 Whether that generates a lot of light or not depends on the characteristics of the light, battery and the wire diameter but he was fairly clear about what he was asking.

This isn't as interesting as our other discussion, but this minor question has been popping up in my head as well.  I think the current will be less than that, perhaps half, because it is spread out over time.  Imagine instead of a continuous array of infinitesimal capacitors, there were just three--one at the beginning of the line, one at the end and one in the middle.  The current across the lamp will be three pulses which are the reactions across the capacitors.  If the wire pair is half a light second long, the interactions will occur at 0s, 1/4s and 1/2s, but we (and the lamp) will observe them at 0s, 1/2s and 1s.  Of course the end is shorted so lets leave the last reaction alone and just look at the middle one.  Apply that idea along the line of infinitesimal capacitors and inductors and you can see that we are continuously putting current into the line, but it is taking longer and longer for each bit of current to come back to us.

[bdunham7]

Your claim equates to having a perfect coupling between those two antennas.  If that's the case, then we clearly have a breakthrough in wireless power transmission!

That would only be the case if it were claimed that there was no EM radiation from the battery-side wire or that the current in the two wires had to be equal. 

[ejeffrey]

The experiment is a bit of a red herring and doesn't really help with the main point of the film that the energy is transferred in the fields.

That is an understatement!  In his zeal to emphasize the the power flow via fields, he essentially states that the fields magically go in some directed way to a load, independent of the wire path.  Yes, there will be a tiny signal at the bulb roughly 3ns after switch closure - you'd no doubt hear a click in an AM receiver placed a meter away, but you won't see any light for at least a second.

The current through the lamp will be Vbatt / (2Zo + Zlamp) starting about 3 ns after switch closure and it will remain approximately the same until the rising edge reflects off the end and returns.
 Whether that generates a lot of light or not depends on the characteristics of the light, battery and the wire diameter but he was fairly clear about what he was asking.

Respectfully disagree.  What would happen if instead we had just 10 meters of wire on each side of the bulb, and 10 meters on each side of the switch/battery, 1 meter apart, but open ended.  For the first 30 ns or so, this setup should be indistinguishable from the Veritasium setup, since nothing could propagate beyond those 10 meters in that first 30 ns.  What you have now are two dipole antennas separated by a meter.  Your claim equates to having a perfect coupling between those two antennas.  If that's the case, then we clearly have a breakthrough in wireless power transmission!

It's ok to have 100% efficiency if I discount conductor losses, dielectric loss and assume no other conductors are nearby to receive power.  Obviously in the real world those assumptions are not true.

Even then the system you described doesn't have 100% transfer.  The voltage across the load is less than the voltage across the battery so even if the currents are equal in the ideal case there is also energy being stored in the fields between the wires.  Some of that is reflected to the battery and some is radiated.

[EEVblog]

I gave up trying, so I just shot a reaction, added the simulation part and a few other bits and it's 45 minutes! 

[sandalcandal]

Sounds like a >45min video.  Will this be the first you attempt a partial script?

I gave up trying, so I just shot a reaction, added the simulation part and a few other bits and it's 45 minutes! 

SPOT ON!

[sandalcandal]

Probably should have commented earlier but in physics it's pretty common to omit units labels in equations and only put the final overall units when giving the final value. So "1/c s" is kinda eh but probably would get full marks in a physics exam (if the rest of the working is correct). It certainly does make the implication of that option less obvious however.

[Seems pretty well addressed later around 19min]

[sandalcandal]

A note on KVL with respect to Maxwell. Many seem to believe that KVL is is derived from Farady's Law (in the correct modern form formulated by Maxwell) as ∮ E • dL=0 and ∑ Vn=0 is a consequence when in reality it is historically the other way around! Kirchoff developed and published his laws of closed loop circuits independently in 1845 *16 years* before Maxwell publish his work on electromagnetics in 1861. You can see the original publication yourself in german here: https://gallica.bnf.fr/ark:/12148/bpt6k151490/f509 The typical introduction to KVL as a derivation of Faraday's law in typical physics pedagogy (and in physics textbooks) is a result of the tendency to introduce the less abstract Faraday's law first. Engineering education often simply states the law as is was originally defined since Faraday's law is often not introduced early in the engineering pedagogy.

[KVL is not a special case of Faraday’s law, it was derived first and exists by itself as a consequence of conservation of energy.]

Some more notes on history here: https://en.wikipedia.org/wiki/Maxwell%27s_equations#Historical_publications

[EEVblog]

Probably should have commented earlier but in physics it's pretty common to omit units labels in equations and only put the final overall units when giving the final value. So "1/c s" is kinda eh but probably would get full marks in a physics exam (if the rest of the working is correct). It certainly does make the implication of that option less obvious however.

My money is on deliberately though 
Didn't know that was common in physics. I of course leave them out regularly because I'm lazy, but you'd get your knuckles rapped by the ruler if you left them off in class.
And even in some companies I've been admonished for leaving them off in reports and analysis.

[EEVblog]

Hmm, I'm watching some of my video again and I do repeat myself a lot. I could probably shave off a few minutes....

[ejeffrey]

[KVL is not a special case of Faraday’s law, it was derived first and exists by itself as a consequence of conservation of energy.]

What?  Of course KVL is a special case of Farady's law.  Specifically it is the case when the time derivative of magnetic flux is zero.  In the presence of time varying magnetic fields ∮E • dL != 0, E by itself is not a conservative field, and therefore voltage is not well defined.

[sandalcandal]

[KVL is not a special case of Faraday’s law, it was derived first and exists by itself as a consequence of conservation of energy.]

What?  Of course KVL is a special case of Farady's law.  Specifically it is the case when the time derivative of magnetic flux is zero.  In the presence of time varying magnetic fields ∮E • dL != 0, E by itself is not a conservative field, and therefore voltage is not well defined.

Maybe the wording could be better but the point there is KVL can be modelled and exists independently to (and historically was discovered/described prior to) Faraday's Law. [Rather than being a "result" of Faraday's Law] Anyway I don't really want to go down the KVL vs Faraday's law and varying definitions of "voltage" rabbit hole again.

[sandalcandal]

I think the LC ladder for Dave's transmission line example is actually "the wrong way around". The ladder should be "rotated 90 degrees" so the inductance elements are in series between the source and the load and the capacitance is in parallel to the source and the load. The L will be very large and the C very small. When you model the ladder correctly between the source and load, you should get the expected delay and dispersion exactly [fairly accurately].

[This nice simulation demo shows how the LC ladder transmission line produces delay] https://www.falstad.com/circuit/e-ladder.html

Edit: Might be good to append for further reading:
"Waveguides" https://www.feynmanlectures.caltech.edu/II_24.html
https://www.allaboutcircuits.com/technical-articles/introduction-to-the-transmission-line/
https://www.allaboutcircuits.com/technical-articles/transmission-lines-from-lumped-element-to-distributed-element-regimes/

[EEVblog]

I think the LC ladder for Dave's transmission line example is actually "the wrong way around". The ladder should be "rotated 90 degrees" so the inductance elements are in series between the source and the load and the capacitance is in parallel to the source and the load. The L will be very large and the C very small. When you model the ladder correctly between the source and load, you should get the expected delay and dispersion exactly.

https://www.falstad.com/circuit/e-ladder.html

Edit: Might be good to append for further reading:
https://www.feynmanlectures.caltech.edu/II_24.html
https://www.allaboutcircuits.com/technical-articles/introduction-to-the-transmission-line/
https://www.allaboutcircuits.com/technical-articles/transmission-lines-from-lumped-element-to-distributed-element-regimes/

Yes, that is the generic equivalent model most people end up using, but I thought that visually it was better to use the full balanced representation here.

[sandalcandal]

Probably should have commented earlier but in physics it's pretty common to omit units labels in equations and only put the final overall units when giving the final value. So "1/c s" is kinda eh but probably would get full marks in a physics exam (if the rest of the working is correct). It certainly does make the implication of that option less obvious however.

My money is on deliberately though 
Didn't know that was common in physics. I of course leave them out regularly because I'm lazy, but you'd get your knuckles rapped by the ruler if you left them off in class.
And even in some companies I've been admonished for leaving them off in reports and analysis.

Yeah I think you did a good job addressing that around 19 min.

[sandalcandal]

I think the LC ladder for Dave's transmission line example is actually "the wrong way around". The ladder should be "rotated 90 degrees" so the inductance elements are in series between the source and the load and the capacitance is in parallel to the source and the load. The L will be very large and the C very small. When you model the ladder correctly between the source and load, you should get the expected delay and dispersion exactly.

https://www.falstad.com/circuit/e-ladder.html

Edit: Might be good to append for further reading:
https://www.feynmanlectures.caltech.edu/II_24.html
https://www.allaboutcircuits.com/technical-articles/introduction-to-the-transmission-line/
https://www.allaboutcircuits.com/technical-articles/transmission-lines-from-lumped-element-to-distributed-element-regimes/

Yes, that is the generic equivalent model most people end up using, but I thought that visually it was better to use the full balanced representation here.

Well, expect to get called out on that then! [The "correct" model would help show the model equivalence with equal resultant delay.]

[EEVblog]

I think the LC ladder for Dave's transmission line example is actually "the wrong way around". The ladder should be "rotated 90 degrees" so the inductance elements are in series between the source and the load and the capacitance is in parallel to the source and the load. The L will be very large and the C very small. When you model the ladder correctly between the source and load, you should get the expected delay and dispersion exactly.

https://www.falstad.com/circuit/e-ladder.html

Edit: Might be good to append for further reading:
https://www.feynmanlectures.caltech.edu/II_24.html
https://www.allaboutcircuits.com/technical-articles/introduction-to-the-transmission-line/
https://www.allaboutcircuits.com/technical-articles/transmission-lines-from-lumped-element-to-distributed-element-regimes/

Yes, that is the generic equivalent model most people end up using, but I thought that visually it was better to use the full balanced representation here.

Found an example
http://web.engr.oregonstate.edu/~traylor/ece391/Andreas_slides/ECE391-S14-Lect1-web.pdf

[EEVblog]

I think the LC ladder for Dave's transmission line example is actually "the wrong way around". The ladder should be "rotated 90 degrees" so the inductance elements are in series between the source and the load and the capacitance is in parallel to the source and the load. The L will be very large and the C very small. When you model the ladder correctly between the source and load, you should get the expected delay and dispersion exactly.

https://www.falstad.com/circuit/e-ladder.html

Edit: Might be good to append for further reading:
https://www.feynmanlectures.caltech.edu/II_24.html
https://www.allaboutcircuits.com/technical-articles/introduction-to-the-transmission-line/
https://www.allaboutcircuits.com/technical-articles/transmission-lines-from-lumped-element-to-distributed-element-regimes/

Yes, that is the generic equivalent model most people end up using, but I thought that visually it was better to use the full balanced representation here.

Well, expect to get called out on that then! [The "correct" model would help show the model equivalence with equal resultant delay.]

Meh. I'm not going to go back and reshoot the entire thing. And it's just yet another thing I'd have to explain. If I just showed the simple model then I'll get people saying "why is there no inductance in the other wire?"
Visually I think that would be a poor representation when trying to compare the two top and bottom like I did.

[sandalcandal]

Found an example
http://web.engr.oregonstate.edu/~traylor/ece391/Andreas_slides/ECE391-S14-Lect1-web.pdf

Derivation for a twin line might be more illustrative, certainly easier for people to see the equivalence... Could also get more hits looking for "Distributed-element model"

[sandalcandal]

Meh. I'm not going to go back and reshoot the entire thing. And it's just yet another thing I'd have to explain. If I just showed the simple model then I'll get people saying "why is there no inductance in the other wire?"

Up to you  I think the Falstad demo is really good at showing how a transmission line with lumped elements produces a delay though...
Which other wire? Both the positive and negative side wires will have series inductance elements with a capacitance between the wires in the "correct" model.

[When I was debating with pure Physics people on KVL stuff before, they were really impressed that the lumped element LC ladder transmission line effectively models electromagnetic wave propagation.]
Edit2: I'm not sure how Kalvin got the "correct" results with a model similar to your's before though... https://www.eevblog.com/forum/chat/veritasium-(yt)-the-big-misconception-about-electricity/msg3828668/#msg3828668
Edit3: Looking at Kalvin's sim closer I think it gets the reflections but doesn't model the delay, which is the primary question.