Veritasium "The Big Misconception About Electricity"

General Electronics
1

Hi!

I am very sure most of you have seen this by now, but it’s such an interesting topic I wanted to start a thread on it, as the public discussion this video has generated is amazing, and there is a lot to be learned here.

on the 19th November, 2021, Veritasium (Derek Muller) posted a video to YouTube titled “The Big Misconception About Electricity” (https://www.youtube.com/watch?v=bHIhgxav9LY), which, in a nutshell discusses the EM fields that are generated in circuits, and that those EM fields travel at the speed of light which can have unexpected consequences. In the video it is shown that a light bulb will be powered by the EM wave before the electrons can reach the bulb.

Whilst what Veritasium says is completely true, I feel that he glosses over many points, and makes a general statement which, without sufficient qualification, is not actually correct - and it is this that has generated the discussion.

To be honest, when I first watched it, I left feeling confused… that I had missed something, or that my understanding of electrical engineering was incorrect. I have since gone back to my text books, to refresh and double check my understanding, some things I hadn’t thought about since college! I can certainly see that for beginners in EE this video could easily create a great deal of confusion, and this is the point of this thread.

The video can easily lead into deeper studies (and checking your understanding of)

  • Electron flow in both AC and DC circuits
  • DC transients vs DC steady state (this is one point I think the video greatly misses)
  • Transmission lines
  • Antennas
  • Electromagnetics and Electrodynamics
  • Maxwell’s equations & Poynting vectors
  • EM radiation (which leads to EMI in practical engineering)

One take away I had (and Dave Jone’s response seconded this) - there is a point where practical engineering gives way to theoretical physics, and you need to know where to draw the line. Certainly having a deeper understanding can help, but simplified models when applied correctly are still enormously valuable - for many, many situations, for all intents and purposes it’s fine to think of electrons flowing in the wires as we do with the water-analogy.

There will always be the possibility to dig deeper, and there is much we still don’t understand, but it doesn’t stop us designing real-world, practical circuits that achieve our purpose and we need to be careful we don’t go deeper than is necessary and allow it to block progress. Sometimes you don’t need to fully understand something to make use of it, it can be ok to accept some “magic” from time to time! For example, we don’t really need to know about quarks to understand how to turn an LED on from a GPIO pin :slight_smile: - and my mother (a maths teacher) has to constantly remind me of this, in school I would find myself constantly diving deeper and deeper into why things are, and that often prevented making practical progress. Remember what your goal is!

with that said, here are some responses to the original video that I enjoyed (or didn’t!)

EEVBlog Response: https://www.youtube.com/watch?v=VQsoG45Y_00
Robert Feranec: https://www.youtube.com/watch?v=Lp_b8gQpxW8
RSD Academy (#1): https://www.youtube.com/watch?v=--v5BXmFYv4
RSD Academy (#2): https://www.youtube.com/watch?v=WRR0gHh9a4s

(personally I found the RSD Academy #1 video to be rather poor, however his second version is much better!)

I would be fascinated to hear what others in our community here think, there are many very experienced engineers in our midst, as one example having followed @scott.xentronics recent webinars on EMI I imagine he would have some thoughts!

(As I write this, the video is trending at #31 on YouTube which is amazing for a science/engineering video and it has started a massive public discussion, which again, is a good thing. Probably the fact that it is not, in my opinion, a great explanation has generated the discussion, which in turn makes it trend, which in turn gets more people involved in the learning process - so, making a poor video, might have been a good thing this time?!)

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When I saw the video the other day it was trending #4 or something. I was surprised at how many of the comments were saying Derrick is wrong! It all seemed perfectly reasonable to me. There is no possible good way of explaining that in a 20 minute video, no matter how detailed! I thought it was quite good for the people it was aimed at, which isn’t PhDs and engineers!

One of the things I picked up at uni was that the skin effect increases as frequency increases, but it can still be a problem at low frequencies (50/60Hz) and high current (2,000A) like in long distance power lines. Otherwise, just ignore it, it’s negligible.

One of the things us engineers are very good at is reducing complex systems down to a simple understandable level, because the truth is that most details are mostly just noise. One of the things that irritates me about Mr EEVblog is how complicated he makes everything sound! Sure you need to be aware of the details, but most of the time you should also mostly ignore them! That’s an engineering judgement call. The physics perspective of how EM waves propagate through a circuit is a curiosity, but only a researcher would need to remember all the details.

I think about it like this: Is it wrong to teach people that the sky is Blue? Because it isn’t. It’s clear. What you say and how much you say depends on the situation, in this case the level of understanding of the other person. Confusing someone, either because you are trying to make yourself look good, or because you’re trying to be accurate, is just counter-productive.

Trying to fully and completely understand EM propagation and current flow will just tie most people’s brains in knots and cause them to doubt the things they thought they already knew. I think something that was missing from the video is that it’s ok to have a “wrong” understanding, because the one you already have is likely also correct, just at a different level, and that’s ok.

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A month or two before the Veritasium video I’d stumbled on an article by some EMC guru on basically the same topic, i.e. “Where does the energy flow in printed circuit boards”, with the answer being “in the dielectric”. This is an instance where knowing the EM theory can be useful in practical applications, as it can help with SI and EMI issues.

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Same anology with the energy in a coil, that’s actually stored in the gap

5

Some very significant simplifying assumptions were made (some that violate quantum physics), though the overall concept of transmission lines was pretty well addressed. Dave Jones’ response showed how the equation in answer “D” was dimensionally incorrect, and that the fundamental errors in the video (indeed, even the nature of external forces driving the propagation of energy) are of use primarily to theoretical physicists. For the vast majority of the rest of us, practical simplifications and the use of lumped parameters are more than enough. The hardest job that designers have is choosing which simplifications to use!

6

I may need to rewatch the video, but i felt he neglected that there are multiple mechanisms at work, and that EM coupling is just one; it might have helped to mention that in the practical example at DC, when the switch is thrown, there would be a short pulse of EM energy then as dV/dt is 0 in steady state there would be no coupling.

and as pointed out many times, getting the dimensions correct and expanding to the effect at 1,2,3,4…n meters would have more adequately explained the point he was making.

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Or as Dan Beeker said, it’s all about the space: https://youtu.be/zHxXj74Pr3o?t=34

1 Like
8

I’m partial to the Science Asylum version of this which is a few years old now: https://www.youtube.com/watch?v=C7tQJ42nGno

This zeros in a little better on the fact that the power is coming from the field.

Resistance is always qualified-away in these types of videos. It would be interesting to see a video that included free-space properties like capacitance, inductance, emission, etc. These are also impediments to the thought experiment from a real-world perspective but their explanations might help build up the charges-and-fields intuition over electrons-doing-work model. (I know, you have to draw a line on which audience somewhere)