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I bought 1000 meters of wire to settle a physics debate [video]

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Re: I bought 1000 meters of wire to settle a physics debate [video]

#151

Why wouldn't a simpler explanation be that the wires produce a radio/electromagnetic wave and that wave gets picked up and induces a current, which is how radio transmitters receivers work?

What's going on -in time- is a lot more complex than the 'steady-state, Occam's razor' simplicity most of us (outside of EE) were fed. One example: the math you'll see in the analysis of 'skin effect'.

https://en.wikipedia.org/wiki/Skin_effect

I hope one of the outcomes of this discussion is that someone will tackle explaining how AC power gets from source to load, and what 'earth grounds' have to do with that ... and WHY. The usual hand-wavy 'simple' discussions leave out WAY too much.

Re: I bought 1000 meters of wire to settle a physics debate [video]

#152
post #96
post #76

So, I genuinely do not get the "controversy" over the Veritasium video. AFAIU, the entire point of the video was to show that electricity travels not through wires but via electric fields ("through the air" so to speak). To illustrate this, he sets up an experiment with parameters such that the conclusion can only mean that some electricity has traveled to the bulb before any could arrive through/around the wires. He…

There's two bits of controversy: 1) Slander: He claims that the way EE is taught is a "lie" but leaves out the many ways that standard EE models agree with his result. 2) Clickbait / inadequate explanation: he leaves out many details in order to make his experiment seem far more mind-blowing that it really is.* Critique 1 can be countered by saying he is targeting a lay audience (say, they took 1 high school physics…

Why wouldn't the effect happen with a circle? Shouldn't the same thing happen just with more delay since they are more separated?

Re: I bought 1000 meters of wire to settle a physics debate [video]

#153
We can make an analogy to trains. Suppose instead of a circuit, we have a long train on a circular track, completely occupying that track. To "turn on" the circuit, we begin to move one of the cars. Now there is slack in their coupling, so a ripple effect occurs: the cars do not all move a the same time, but a wave of motion begins, and this propagates in both directions around the circular track, away from the initially moved car. Eventually, both these ripples reach the opposite side of the circular track where the motion starts to occur and can be used to do some work. Then we can get into a more or less steady state: the cars are moving around the track.

This steady state of motion is like "drift current", whereas the initial ripple of couplings clattering together an initiating the motion is like the electric field propagating through the circuit.

Of course, EE's know about drift current, transmission line behavior and other topics.

Re: I bought 1000 meters of wire to settle a physics debate [video]

#154
post #96
post #76

So, I genuinely do not get the "controversy" over the Veritasium video. AFAIU, the entire point of the video was to show that electricity travels not through wires but via electric fields ("through the air" so to speak). To illustrate this, he sets up an experiment with parameters such that the conclusion can only mean that some electricity has traveled to the bulb before any could arrive through/around the wires. He…

There's two bits of controversy: 1) Slander: He claims that the way EE is taught is a "lie" but leaves out the many ways that standard EE models agree with his result. 2) Clickbait / inadequate explanation: he leaves out many details in order to make his experiment seem far more mind-blowing that it really is.* Critique 1 can be countered by saying he is targeting a lay audience (say, they took 1 high school physics…

> He claims that the way EE is taught is a "lie"

The thing is: this is sort of true. Now, all electrical engineers are very familiar with transmission line theory, that's pretty much their bread and butter. And all EEs know that if you're not working with well-defined transmission lines (like coaxial cables), you need to use a field solver. 2D field solvers are often sufficient, but if not 3D field solvers can and will be used.

And then most of those same EEs, despite having just used a field solver which clearly shows that all the power is in the fields, which are in the dielectric space between the conductors, persist in using the mental model that electrical power moves in wires.

This isn't just a pedantic quibble. There are real, practical effects. If you're designing a PCB and you have two signal lines with overlapping fields, those signals are going to couple, which will create common mode current, which will cause an EMI problem. You can stop those signals coupling by making them reference different ground planes, which makes the fields no longer overlap. If you route a signal line from one side of a ground plane to the other, you have to provide a path for the fields to get to the other side of the ground plane (i.e. "route" the dielectric, generally with a ground via), because if you don't, they will find their own path anyway and you won't like the results.

If you persist in thinking that electrical power flows through wires, these sorts of effects are mysterious and only explicable through the magical black box that is a field solver. If, on the other hand, your mental model is that electrical power is in the fields, then -- surprise! -- the results of a field solver won't be so mysterious any more.

And if you have a more accurate mental model, if you can predict more or less how the fields will behave before looking at the results of the field solver, then that means you can design with the fields in mind, rather than just tweaking things until the field solver stops being angry at you, but not actually understanding why the design works in the end.

Don't believe me? Here's Rick Hartley, an extraordinarily experienced PCB designer: https://www.youtube.com/watch?v=QG0Apol-oj0&t=1102s

I found the responses from other EEs on youtube like Electroboom and EEVBlog disappointing. You can quibble about details of how he presented it (like, saying 1/c rather than 1m/c), but Maxwell's equations are the correct description of how electricity works, and Veritasium is absolutely correct in his core point which is that power flows outside the wires. Other models, such as lumped-element and transmission lines can suffice for many purposes but are ultimately wrong. Rather than responding towards him with hostility, perhaps they should have considered if their own mental models weren't quite as accurate as they had thought.

As a final note, the problem as presented by Veritasium can't be accurately modeled by anything less than Maxwell's equations (i.e. a field solver), but you can get most of the way with transmission line theory and tweaking it with some physical common sense. Closing the switch causes electric and magnetic fields to propagate across the gap between the switch and the light bulb, and down the two transmission lines, at the speed of light (modified by the relative permittivity). The current that will initially flow across the light bulb, once the fields reach it, can be calculated from the characteristic impedance of two parallel wires acting as a transmission line. When the signals reach the end of the transmission lines, they will "see" a short and reflect with opposite voltage; when that opposite-voltage signal reaches the switch and light bulb the transmission lines act like a short and from that point on the light-bulb receives the full current. That 1m/c delay, in particular, isn't accounted for by transmission line theory at all. The way you get that (without a field solver) is by knowing that electrical power is in the fields, which propagate at the speed of light. Since transmission line theory can't accurately model the problem in full, I think Veritasium can be forgiven for not mentioning it (especially since he was targeting a general audience).

Re: I bought 1000 meters of wire to settle a physics debate [video]

#155
post #76

So, I genuinely do not get the "controversy" over the Veritasium video. AFAIU, the entire point of the video was to show that electricity travels not through wires but via electric fields ("through the air" so to speak). To illustrate this, he sets up an experiment with parameters such that the conclusion can only mean that some electricity has traveled to the bulb before any could arrive through/around the wires. He…

EEVblog goes into depth about the video, basically calling it out and explaining the how and why the headline is misleading.

https://youtu.be/VQsoG45Y_00

Re: I bought 1000 meters of wire to settle a physics debate [video]

#157

Earlier quoted context omitted.

> some electricity I think the key part of the controversy is the word "some". In the original Veritasium video it pretty strongly implies that enough energy to light the bulb, i.e. virtually all the electricity, is traveling instantaneously a short distance rather than "through" the wire. A big part of that video is to essentially say you're wrong if you understand electrons moving through the wire as how electricit…

>you're wrong if you understand electrons moving through the wire as how electricity works in direct current, how does charge move from one terminal to another if it's not carried by electrons (which often act as waves)?

Moving charge isn't how power transfer in electricity mainly works, that's the point. Moving electrons is less than half of the story.

Re: I bought 1000 meters of wire to settle a physics debate [video]

#158
post #45

This is basic transmission line theory. https://en.wikipedia.org/wiki/Transmission_line

It may be basic, but just the _existence_ of this field wasn't something that was on my radar, let alone all the details and implications. This was certainly the most interesting and enlightening set of videos I've seen this year. I particularly like this one because "I want to get an oscilloscope and see what is actually going on" was my first thought, and this video saves me the effort of trying to set up what woul…

You should watch Electroboom's analysis if you want the full details from an electrical engineer:

https://youtu.be/iph500cPK28

Re: I bought 1000 meters of wire to settle a physics debate [video]

#159
post #76

So, I genuinely do not get the "controversy" over the Veritasium video. AFAIU, the entire point of the video was to show that electricity travels not through wires but via electric fields ("through the air" so to speak). To illustrate this, he sets up an experiment with parameters such that the conclusion can only mean that some electricity has traveled to the bulb before any could arrive through/around the wires. He…

Anecdotally, as a novice, I was left really confused by Veritasium’s video, whereas after watching this video I feel (hopefully accurately) like I basically understand the situation. If people are missing the point of Veritasium’s video, maybe that’s because it didn’t make its point very clearly…

Re: I bought 1000 meters of wire to settle a physics debate [video]

#160
post #154
post #96

Earlier quoted context omitted.

There's two bits of controversy: 1) Slander: He claims that the way EE is taught is a "lie" but leaves out the many ways that standard EE models agree with his result. 2) Clickbait / inadequate explanation: he leaves out many details in order to make his experiment seem far more mind-blowing that it really is.* Critique 1 can be countered by saying he is targeting a lay audience (say, they took 1 high school physics…

> He claims that the way EE is taught is a "lie" The thing is: this is sort of true. Now, all electrical engineers are very familiar with transmission line theory, that's pretty much their bread and butter. And all EEs know that if you're not working with well-defined transmission lines (like coaxial cables), you need to use a field solver. 2D field solvers are often sufficient, but if not 3D field solvers can and wi…

Is there really an epidemic of EE's who know how to use a field solver, but don't know to consider coupling between signal lines? My intuition is the opposite of yours: most EEs actually know the ideas from the Veritasium video. Therefore, the way EE is taught is not a lie, since it includes that knowledge.

(For completeness, the alternate take is that Veritasium was claiming "the way _elementary_ EE is taught is a lie" -- but that still leaves Veritasium having left out critical context for such an audience)

> I found the responses from other EEs on youtube like Electroboom and EEVBlog disappointing. [...] Rather than responding towards him with hostility, perhaps they should have considered if their own mental models weren't quite as accurate as they had thought.

Personally, I didn't get hostility from any of their videos. They were just injecting some engineering sensibility to bridge the gap between most people's EE knowledge and Derek saying "everything you've been taught is a lie."

Also, to my recollection they both absolutely attested that yes Maxwell's equations are the correct description which supports Derek's results (modulo Electroboom's callout about the bulb actually always being on)

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