Author Topic: "Veritasium" (YT) - "The Big Misconception About Electricity" ?  (Read 209336 times)

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Offline sandalcandal

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #100 on: November 22, 2021, 08:42:10 am »
Here is a simulation for 10 seconds (and the corresponding LTSpice files). It is possible to see how the energy propagates through the long wires [lossless transmission lines] back and forth, and how the system converges gradually to the steady state, and how the load will then receive full power. I increased the load to 200 ohms, so that we would see some reflections.

Note: I had to add .txt file extension to the plot settings file due to forum filename restrictions. Just rename the plot settings file as Veritasium_long_cable_c.plt.
Nice, looks pretty much exactly like the plots in the slides Derek/Veritasium shared. https://ve42.co/bigcircuit
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Offline Kalvin

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #101 on: November 22, 2021, 08:51:31 am »
Here is a simulation for 10 seconds (and the corresponding LTSpice files). It is possible to see how the energy propagates through the long wires [lossless transmission lines] back and forth, and how the system converges gradually to the steady state, and how the load will then receive full power. I increased the load to 200 ohms, so that we would see some reflections.

Note: I had to add .txt file extension to the plot settings file due to forum filename restrictions. Just rename the plot settings file as Veritasium_long_cable_c.plt.
Nice, looks pretty much exactly like the plots in the slides Derek/Veritasium shared. https://ve42.co/bigcircuit

Great, the professors were able to model & simulate the circuit correctly as well. :P
« Last Edit: November 22, 2021, 08:53:18 am by Kalvin »
 
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Online RoGeorge

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #102 on: November 22, 2021, 08:57:48 am »
LTSpice is able to simulate transmission lines pretty well

True that.  The speed of light is already taken into account (indirectly) by setting the delay in the TL.

Consider the loop equivalent here:

never mind that the wire loops at each end at the 1/2 light second distance.  Even if the ends were open, the lamp would still receive power in the time it takes light to travel 1 meter from switch & battery to lamp

Indeed.

 :palm:

I was wrong all the time this thread, thank you all.  ;D
 
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Offline BrianHG

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #103 on: November 22, 2021, 09:08:41 am »
LTSpice is able to simulate transmission lines pretty well

True that.  The speed of light is already taken into account (indirectly) by setting the delay in the TL.

Consider the loop equivalent here:

never mind that the wire loops at each end at the 1/2 light second distance.  Even if the ends were open, the lamp would still receive power in the time it takes light to travel 1 meter from switch & battery to lamp

Indeed.

 :palm:

I was wrong all the time this thread, thank you all.  ;D
The difficulty  in understanding whats going on is that "Veritasium" has a clever setup of having the loop a parallel ultra long wires, spaced apart by 1 meter all along the way.  With a degree of BS assumptions, like the cable and switch having 0 resistance, the battery having millions of amps of current with 0 ohm impedance, and the lamp being infinitely high in impedance.  What you end up with is the equivalent of 1 gigantic dipole antenna on the battery and switch side making a massive VLF transmitter at switch on, while on the lamp side, you have the parallel receiving dipole antenna.
« Last Edit: November 22, 2021, 09:10:55 am by BrianHG »
 

Offline EEVblog

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #104 on: November 22, 2021, 09:17:21 am »
One can even calculate how much current would flow initially: the long cables are transmission lines with a characteristic impedance. With 1 m distance (and huge diameter to kepp the resistance low) likely with a charcteristic impedance somewhere in the 100 ohms range (no more than 370 Ohms for the free space).
For the initial time the transmission line act just like resistors of the characteristic impedance, only with some delay (1 second for the link at the end) the end and wire resistance is seen.

What about the (huge) line capacitance?
 

Offline Kalvin

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #105 on: November 22, 2021, 09:22:13 am »
One can even calculate how much current would flow initially: the long cables are transmission lines with a characteristic impedance. With 1 m distance (and huge diameter to kepp the resistance low) likely with a charcteristic impedance somewhere in the 100 ohms range (no more than 370 Ohms for the free space).
For the initial time the transmission line act just like resistors of the characteristic impedance, only with some delay (1 second for the link at the end) the end and wire resistance is seen.

What about the (huge) line capacitance?

The inductance and capacitance is distributed across the long parallel wires -> transmission line.
 

Offline BrianHG

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #106 on: November 22, 2021, 09:25:25 am »
One can even calculate how much current would flow initially: the long cables are transmission lines with a characteristic impedance. With 1 m distance (and huge diameter to kepp the resistance low) likely with a charcteristic impedance somewhere in the 100 ohms range (no more than 370 Ohms for the free space).
For the initial time the transmission line act just like resistors of the characteristic impedance, only with some delay (1 second for the link at the end) the end and wire resistance is seen.

What about the (huge) line capacitance?

In the image, the wire is in space, IE a vacuum.
Unshielded.  (IE, no plastic/rubber/enamel coating.)
An impossible perfect 0 ohm impedance superconductor at ~4 degree kelvin, IE the background temp of deep space.  (So long as the cable was shielded from our sun-light.)

Yes, I guess there has still got to be some capacitance, especially between a 1 light second long parallel cable with only 1 meter distance.
 

Offline EEVblog

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #107 on: November 22, 2021, 09:25:42 am »
Here is a simulation for 10 seconds (and the corresponding LTSpice files). It is possible to see how the energy propagates through the long wires [lossless transmission lines] back and forth, and how the system converges gradually to the steady state

But the trick is what happens at steady state?
How does the "energy flow in the field" then?

Who is this video even for anyway? It's not a "gotcha" for practical engineers that's for sure.
If it's for phsyics students and the lay person then it's an ok top level primer about fields and poynting vectors. But there is nothing of practical worth beyond that.
And the undersea transmission thing was just asserted without any real discussion.
 

Offline EEVblog

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #108 on: November 22, 2021, 09:27:50 am »
One can even calculate how much current would flow initially: the long cables are transmission lines with a characteristic impedance. With 1 m distance (and huge diameter to kepp the resistance low) likely with a charcteristic impedance somewhere in the 100 ohms range (no more than 370 Ohms for the free space).
For the initial time the transmission line act just like resistors of the characteristic impedance, only with some delay (1 second for the link at the end) the end and wire resistance is seen.

What about the (huge) line capacitance?

The inductance and capacitance is distributed across the long parallel wires -> transmission line.

Yes, the capacitance of which is pre-charged prior to switch on.
 

Offline sandalcandal

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #109 on: November 22, 2021, 09:30:20 am »
Who is this video even for anyway? It's not a "gotcha" for practical engineers that's for sure.
If it's for phsyics students and the lay person then it's an ok top level primer about fields and poynting vectors. But there is nothing of practical worth beyond that.
And the undersea transmission thing was just asserted without any real discussion.
The undersea cable and some into to transmission line theory seems like a nice video idea.
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Offline BrianHG

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #110 on: November 22, 2021, 09:30:34 am »
Who is this video even for anyway? It's not a "gotcha" for practical engineers that's for sure.
If it's for phsyics students and the lay person then it's an ok top level primer about fields and poynting vectors. But there is nothing of practical worth beyond that.
And the undersea transmission thing was just asserted without any real discussion.

And you just hit the cusp of the odd issue since the layout is specifically oriented to not necessarily try, but just ended up being a cheap 'gotcha' exclusively for those who are learning the theory if you miss the key concept in the illustration.  It even tricked me having to look twice.  This video will definitely not click with Veritasium's larger audience.
« Last Edit: November 22, 2021, 09:38:39 am by BrianHG »
 

Offline EEVblog

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #111 on: November 22, 2021, 09:35:49 am »
Who is this video even for anyway? It's not a "gotcha" for practical engineers that's for sure.
If it's for phsyics students and the lay person then it's an ok top level primer about fields and poynting vectors. But there is nothing of practical worth beyond that.
And the undersea transmission thing was just asserted without any real discussion.
The undersea cable and some into to transmission line theory seems like a nice video idea.

Still thinking about how I'll approach this video.
I reacted to it in my live show the other day, and I justed edit that bit from it. Thought about just uploading that on the 2nd channel, but I think it might make a good introduction to a discussion video response on the main channel.
At the moment I'm thinking to take the approach as above and point out that this video has little practical utility to engineers, how none of this is new, what about DC setady state, and maybe a few basic calcs and discussion on how the circuit configuration matters.
 

Offline Kalvin

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #112 on: November 22, 2021, 09:37:04 am »
And the undersea transmission thing was just asserted without any real discussion.

The undersea transmission cable was an example for illustrating the fact that the "water hose" model (ie. moving electrons are carrying the current) was wrong, and the the actual model is transmission line em-model. If the "water hose" model was correct, the cable would have worked ok. But since the the cable had to be modeled as a lossy transmission line, and the lossy transmission line introduces signal distortion, the morse symbols were badly distorted. In order to compensate these distortions, the loading coils were added.
 

Offline sandalcandal

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #113 on: November 22, 2021, 09:38:46 am »
Still thinking about how I'll approach this video.
I reacted to it in my live show the other day, and I justed edit that bit from it. Thought about just uploading that on the 2nd channel, but I think it might make a good introduction to a discussion video response on the main channel.
At the moment I'm thinking to take the approach as above and point out that this video has little practical utility to engineers, how none of this is new, what about DC setady state, and maybe a few basic calcs and discussion on how the circuit configuration matters.
Sound's like a reactionary rant video :-DD Maybe a bit more focus to helping add new information.
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Offline BrianHG

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #114 on: November 22, 2021, 09:44:55 am »
Still thinking about how I'll approach this video.
I reacted to it in my live show the other day, and I justed edit that bit from it. Thought about just uploading that on the 2nd channel, but I think it might make a good introduction to a discussion video response on the main channel.
At the moment I'm thinking to take the approach as above and point out that this video has little practical utility to engineers, how none of this is new, what about DC setady state, and maybe a few basic calcs and discussion on how the circuit configuration matters.
Sound's like a reactionary rant video :-DD Maybe a bit more focus to helping add new information.
Yes, stay away from a reactionary rant style video.  Offering useful new information, (advanced route) like how the effect itself can cause harm to someones intended project and how to work around or work with would be far better, or (more practical route) what typically happens in real life when you switch power on long wires.
 

Offline rs20

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #115 on: November 22, 2021, 09:46:44 am »
Quite aside from debating what the example circuit would do, I really dislike the "OMG everything you've been taught in school is WRONG" style of video like this. Especially when what was ostensibly wrong at school is actually correct, or at least correct enough for everyday use (and even some fields of advanced engineering usage) and far more convenient that solving multiple 3D fields.

For example, he goes on about the pulling chain back and forth example at the start. And implies that there's no way to explain that and just abandons that point there and then. When actually, P = V*I, and reversing both the voltage and the current doesn't change the sign of the power flow: P = -V * -I.

So in the simple model, both V and I regularly invert in an AC system, and P = V * I stays positive.
In the poynting model, both E and H regularly invert in an AC system, and PoyntingVector = E x H stays pointing in the same direction. It's the same damn thing.

But no, for maximum clickbait and sensationalism, let's just fail to explain how the conventional high school explanation addresses the question, and throw every physics high school teacher in the world under the bus while they fend off students parroting this video. (OK, to be fair, that might be overreaching, I don't know if that's actually much of a problem. But I can't help but wonder if this video is diseducational on balance.)
 
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Offline IanB

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #116 on: November 22, 2021, 09:56:31 am »
I think the point of the video, if you get past the specific set-up of battery and lamp and implausibly long wires, is the question: "What is the propagation delay between the source and the sink?"

In other words, when you close the switch near the battery, how long is it before the load can detect that something has happened?

Is the propagation delay determined by the length of the wires in the circuit, or is it determined by the straight line distance in free space?

The answer seems to be the straight line distance, and this would be true regardless of the circuit configuration. You do not have to have long, straight, parallel wires 1 meter apart. The wires could take any convoluted path and be any shape, and the answer would be the same. If the "detector" is 1 m away from the "transmitter", then the detector can determine that something has happened at a time 1/c after the event?

The relevance of the undersea cable is that although detection of an event could happen after time 1/c, there is no guarantee that the signal shape will be preserved. It could be horribly distorted (and attenuated) when it arrives.
« Last Edit: November 22, 2021, 09:58:37 am by IanB »
 

Offline EEVblog

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #117 on: November 22, 2021, 09:56:36 am »
Still thinking about how I'll approach this video.
I reacted to it in my live show the other day, and I justed edit that bit from it. Thought about just uploading that on the 2nd channel, but I think it might make a good introduction to a discussion video response on the main channel.
At the moment I'm thinking to take the approach as above and point out that this video has little practical utility to engineers, how none of this is new, what about DC setady state, and maybe a few basic calcs and discussion on how the circuit configuration matters.
Sound's like a reactionary rant video :-DD Maybe a bit more focus to helping add new information.

Here is my initial reaction when people pointed it out without having watched it or even knowing the title


You can see my initial engineering reaction with my mind instantly going to skin effect and that energy is in the magnetic field, and that "he's probably not wrong", but it's not a practical way of looking at it. Enter transmission lines etc.
I suspect that would be most engineers reaction as well?
 
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Offline EEVblog

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #118 on: November 22, 2021, 09:59:57 am »
The relevance of the undersea cable is that although detection of an event could happen after time 1/c, there is no guarantee that the signal shape will be preserved. It could be horribly distorted when it arrives.

How exactly does this relate to (essentially) "we didn't take into account that the energy flows in the field"?
This is a transmission line theory question, not a fundamental physics one.
 

Offline IanB

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #119 on: November 22, 2021, 10:08:39 am »
How exactly does this relate to (essentially) "we didn't take into account that the energy flows in the field"?
This is a transmission line theory question, not a fundamental physics one.

I think the video is about fundamental physics, not initially about engineering or transmission lines.

On the undersea cable example, if it would be correct physics to say that the transmission of a signal through the cable happens purely by electrical impulses inside the metal of the conductor, then distortion would not be expected. It is only when you bring in the physical understanding that the signal propagation depends on the surrounding environment outside the cable that you can explain the distortion.
 
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Offline EEVblog

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #120 on: November 22, 2021, 10:17:19 am »
On the undersea cable example, if it would be correct physics to say that the transmission of a signal through the cable happens purely by electrical impulses inside the metal of the conductor, then distortion would not be expected. It is only when you bring in the physical understanding that the signal propagation depends on the surrounding environment outside the cable that you can explain the distortion.

Sound like they didn't know how to make proper control impedance transmission lines...
 

Offline sandalcandal

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #121 on: November 22, 2021, 10:21:19 am »
Not to say you can't take advantage of the debate/hype around the Veritasium video but would be good to keep it "useful" and not too much of an elitist wank.

You can see my initial engineering reaction with my mind instantly going to skin effect and that energy is in the magnetic field, and that "he's probably not wrong", but it's not a practical way of looking at it. Enter transmission lines etc.
I suspect that would be most engineers reaction as well?

Yeah, reading comments here, I think one of the big things the video completely missed was that you can (and the professors referenced by Derek do this) model the system using transmission lines (or an antenna). That could be an interesting "new" take. Maybe can make something click baity like "Energy DOES flow through the wire" since that's what we do in EE all the time, the "catch" is the "wire" needs to be properly modelled as a transmission line then can also talk a bit more about how they didn't back in the day of the first under sea cable.

[Should be acknowledged the underlying physics is equivalent/true though]
« Last Edit: November 22, 2021, 10:25:08 am by sandalcandal »
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Offline IanB

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #122 on: November 22, 2021, 10:23:39 am »
Sound like they didn't know how to make proper control impedance transmission lines...

Did you know how to do that in 1858?

Edit: Maxwell's equations were first introduced around 1861.

I would argue that transmission lines are not part of fundamental physics, they are a higher level abstraction introduced in electrical engineering to make design tasks easier. A transmission line is an artifact, a thing created by electrical engineers by applying fundamental physics in a certain, controlled way to a particular arrangement of circuit elements.
« Last Edit: November 22, 2021, 10:28:12 am by IanB »
 

Offline EEVblog

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #123 on: November 22, 2021, 10:23:59 am »
But I can't help but wonder if this video is diseducational on balance.

I was thinking the same thing.
If it was titled something like "How energy flows in electromagnetic fields", and the sensationalit stuff was left out, then it become a very valuable explanation.
But the way it's titled and scripted, one could argue it does more harm than good. Especially for engineering students.
There is nothing new here for an engineering student. We are taught about (slow) electron drift velocity, and that energy is stored and transported in electric and magentic fields, it's all fundamental stuff.
It's basically just picking a physics fight like Walter Lewin did with KVL, and Electroboom calling him out from the practical engineering aspect.
 
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Offline EEVblog

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Re: "Veritasium" (YT) - "The Big Misconception About Electricity" ?
« Reply #124 on: November 22, 2021, 10:26:17 am »
Sound like they didn't know how to make proper control impedance transmission lines...

Did you know how to do that in 1858?
I would argue that transmission lines are not part of fundamental physics, they are a higher level abstraction introduced in electrical engineering to make design tasks easier. A transmission line is an artifact, a thing created by electrical engineers by applying fundamental physics in a certain, controlled way to a particular arrangement of circuit elements.

Correct, because engineering is an applied science. This would have been one of the early development in the field (pun intended) of transmission line theory. Yet he doesn't mention transmission lines at all does he? (I still haven't watch the entire thing from end to end)
It's just a physicist talking theoretical physics for the sake of theoretical physics.
« Last Edit: November 22, 2021, 10:27:58 am by EEVblog »
 


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