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

[adx]

The concept of power 'travelling' is interesting in itself.  If you have a motor transmitting rotational power (torque x speed) through a shaft to a load in a completely constant manner, so that the energy of the shaft--which consists of the angular momentum and flex torsion--is absolutely constant, how does the power 'travel'?  No energy is going in or out of the shaft itself, yet power is applied at one end and applied to the load at the other.  Likewise, the static fields of a DC system store some energy, but since they are static and their energy never increases or decreases, can you say that energy flows 'through' them even though it doesn't flow in or out?  Even if you do (a semantic issue IMO), you'd have to concede that this is at least nominally distinguishable from the case where energy is put into a field, it's energy measurably increases and then at a later time and perhaps at a different location, that energy is dissipated in a load and the field's energy decreases.

That mechanical system (and ones like it, ie circuits) is what I have been grappling with.

But I have to concede that for the electrical system you describe, energy does have to be put into those field(s) to make it work, so the DC analysis is a kind of fallacy (in that there is always going to be stored energy which is there and can conceptually be taken from, and refuelled at the other end). This is central to my gripe with Bernoulli's principle and its (I say false) assumption of conservation of energy. The system has to be charged up before it will work, and energy is different for different arrangements. Same for Bud's situation of a wire going through a copper shielding plate: The DC situation is identical and no one has yet addressed my comment "The bulk of the magnetic field will be in a place with no electric field." (similar to what you were saying about the circuit encased in other materials but otherwise physically identical). To charge such a system up, either energy has to be dissipated in the plate ("The magnetic field at DC will go straight through a copper plate.") or squeeze into the gap "like a black hole" (magnetic), or none of these if no plate. These are different systems with different energy content (potential energy, or not, which is why I was  going on about that, and conservation of energy), with identical DC behaviour (in terms of current and pressure differences). It's also why I was trying but failing to "stick solely to DC".

I noticed the energy always transfers along the current path and transverse to the pressure gradient, so it is not possible to place or test the position of its flow, as soon as the flow heads along the direction of the gradient, work appears (or disappears).

[StillTrying]

Going back to the 1st post and video, shirley I could test this with a blue LED, photodiode and ~20m of wire.

[adx]

Going back to the 1st post and video, shirley I could test this with a blue LED, photodiode and ~20m of wire.

Or an SFP module with lens fitted to make a cheap but fast 1 pixel camera.

[bdunham7]

How is the Poynting vector useless when it is the answer, the solution to what was being discussed?
To know what is 'really' going on (and 'really' here means in the context of classical electrodynamics, at least for me) is the whole point of the discussion.

If that is your goal, OK.  My point simply is that once you have characterized the system sufficiently to be able to determine the Poynting vectors and calculate your S-field, you have a complete model.  Actually calculating the vectors and S-field doesn't give you any practical new information in the DC case AFAIK.  It just gives you a representation.

[tszaboo]

OK, I think I understand the 1/C comment now, and have an engineering explanation for it, which is. So imagine the signal starts travelling down from the wire. It will create RF interference. Now this interference needs to travel 1m only, and it will then arrive at the antenna, which is near the lightbulb. It takes it 1/C. And Veritasium said, any power will turn the light on, so technically it will be on. So he is technically right. But honestly, this is so unrealistic, that it is against how we deal with electricity.

[EEVblog]

@Bud: The magnetic field at DC will go straight through a copper plate. The electric field AKA voltage difference will crowd into the gap. From this time of night I can't see how that makes you wrong. The bulk of the magnetic field will be in a place with no electric field.

But does the current create the magnetic field, or does the magnetic field create the current?

[EEVblog]

"The Poynting Vector is pointless."

Please, kindly, toss all your coax cables out the window then.

Apparently you missed the context.  I was referring to steady-state DC circuits exclusively, which ironically I often use coax cables for--but that's a different issue.  And I didn't say that they (Poynting vectors) can't be calculated, drawn or that they somehow don't apply--I said that they are poyntless in that they serve no purpose other than to give you the smug satisfaction that you are above all the other heathens because you somehow "know what is really going on".

Anyone who brings up poynting vectors in DC circuit theory will be laughed out of any engineering classroom or lab.

[Kalvin]

@Bud: The magnetic field at DC will go straight through a copper plate. The electric field AKA voltage difference will crowd into the gap. From this time of night I can't see how that makes you wrong. The bulk of the magnetic field will be in a place with no electric field.

But does the current create the magnetic field, or does the magnetic field create the current?

Yes.

[SandyCox]

Allow me to add another worm to the can: The original version of Poynting's theorem only applies to nondispersive linear materials.

Sandy

[HuronKing]

"The Poynting Vector is pointless."

Please, kindly, toss all your coax cables out the window then.

Apparently you missed the context.  I was referring to steady-state DC circuits exclusively, which ironically I often use coax cables for--but that's a different issue.  And I didn't say that they (Poynting vectors) can't be calculated, drawn or that they somehow don't apply--I said that they are poyntless in that they serve no purpose other than to give you the smug satisfaction that you are above all the other heathens because you somehow "know what is really going on".

Anyone who brings up poynting vectors in DC circuit theory will be laughed out of any engineering classroom or lab.

You say that but I teach DC and AC circuit theory at my university alma mater, so...   

[Howardlong]

"The Poynting Vector is pointless."

Please, kindly, toss all your coax cables out the window then.

Apparently you missed the context.  I was referring to steady-state DC circuits exclusively, which ironically I often use coax cables for--but that's a different issue.  And I didn't say that they (Poynting vectors) can't be calculated, drawn or that they somehow don't apply--I said that they are poyntless in that they serve no purpose other than to give you the smug satisfaction that you are above all the other heathens because you somehow "know what is really going on".

Anyone who brings up poynting vectors in DC circuit theory will be laughed out of any engineering classroom or lab.

You say that but I teach DC and AC circuit theory at my university alma mater, so...   

I wonder how many EEs, as opposed to physicists, have had a practical use for directly using Poynting vectors or Maxwell's equations since leaving university? Sure we all know the right- and left-hand rules, and an RF engineer might well have use them indirectly when using an EM or antenna modelling package, put I doubt most EEs will have touched them, or have had a need to do so directly, since leaving the classroom.

[bsfeechannel]

Yes.  "Demonstrating" a theoretical concept with an example that cannot be modelled

Modeled with what model? With the model of your misconception? That's precisely the point of Derek's video: show that your model doesn't work.

--requires conditions that cannot exist and neglecting factors that would swamp the claimed effect in the real world--is just showmanship, not education.

Someone here in this thread reproduced his experiment using shorter wires, pulse generators and an oscilloscope capable of detecting picoseconds.

Derek's thought experiment used components familiar to a broad audience.

Education is about showing that your life is a lie. What you think you know is an illusion.

I've said in other discussions that there is absolutely no need to teach electronics at any level with exemplar circuits that do not work properly, or would be totally impractical, because it is always feasible--and better in the long run--to do a bit of extra work and provide a realistic, practical example.  The same goes for this case.

What is more practical than a battery, a switch, wires and a lamp?

  He creates a false dichotomy--false because power actually won't get from the generating plant to your house if the electrons don't actually move in the wires and that motion is inextricably connected to the fields involved--and then 'proves' it with a non-falsifiable 'experiment' where he visually misrepresents what he is saying and demands physically impossible conditions to boot.  Will the exact light bulb he uses in the video light in the manner he shows in that video with a current of 6 milliamperes or less?

His experiment is falsifiable, because you can reproduce it in dimensions other than wires extending 300.000 km. He just chose those dimensions because it gives round numbers like 1 second, 2 seconds, etc. Time delays that are intuitive to a non specialized audience.

[bsfeechannel]

Without clarity from Derek, my take is that the vagueness is deliberate: thus, I take it to be a trick question. Kinda disappointed to be honest, especially as the etymology for "veritasium" is rooted in the latin word for "truth". The more I think about it, the more I['m coming the the conclusion that the original video was more about clicks and engagement than it was about truth.

You don't have to guess at that, Derek himself did an entire video saying that going forward his videos were going to be optimised for viral views and clicks. He succeeded, he knew very well this would bring an avalance of responses from engineers. You can almost see the joy on his face as the professors told him he would get called out on it.

They didn't say Derek would be called out because engineers know best. Quite the opposite. Engineers are essentially dumbed-down "physicists". But that's not a problem. The problem is that most of them don't know that and some of them keep pestering physicists when physicists show them the limitations of their knowledge.

We, engineers, need to stop this. We need to acknowledge that physicists hold all the keys to our knowledge.

[bsfeechannel]

Anyone who brings up poynting vectors in DC circuit theory will be laughed out of any engineering classroom or lab.

Not quite. I'm an engineer and I would never do that. What engineers, and even the so called "practical" (God, I hate that word in this context) engineer, think or do is not defined by what you or Mehdi think engineers think or do. Although both of you are popular entertainers, the limitations of your insight into the everyday electromagnetic phenomena is showing.

There are practical engineers who do understand and use Maxwell's equations for their regular jobs and are grateful when physicists show the limitations of their misconceptions.

This physicist vs engineers feud is a just a fabrication.

[bsfeechannel]

But that's the point of it all.
Derek's question and answer were obviosuly a troll, so Medhi successfully trolled back.

The difference is that Derek didn't lie in his video. Mehdi did.

[EEVblog]

Without clarity from Derek, my take is that the vagueness is deliberate: thus, I take it to be a trick question. Kinda disappointed to be honest, especially as the etymology for "veritasium" is rooted in the latin word for "truth". The more I think about it, the more I['m coming the the conclusion that the original video was more about clicks and engagement than it was about truth.

You don't have to guess at that, Derek himself did an entire video saying that going forward his videos were going to be optimised for viral views and clicks. He succeeded, he knew very well this would bring an avalance of responses from engineers. You can almost see the joy on his face as the professors told him he would get called out on it.

They didn't say Derek would be called out because engineers know best.

I never said nor implied that. Engineers will however have a very different take on it, and for very practical reasons.

Remember, NONE of this discussion, this thread, all the videos responses etc would exist if Derek hadn't put that trolling question in.

[EEVblog]

But that's the point of it all.
Derek's question and answer were obviosuly a troll, so Medhi successfully trolled back.

The difference is that Derek didn't lie in his video. Mehdi did.

 

[EEVblog]

They didn't say Derek would be called out because engineers know best. Quite the opposite. Engineers are essentially dumbed-down "physicists". But that's not a problem. The problem is that most of them don't know that and some of them keep pestering physicists when physicists show them the limitations of their knowledge.
We, engineers, need to stop this. We need to acknowledge that physicists hold all the keys to our knowledge.

Nobody here is denying that the physics isn't right. We are pointing out that there are ALSO ways that engineers look at these sorts of problems, and for good reason. And it also gives people ANOTHER WAY to look at the problem and get the same answer. That's a good thing. Not everyone is best served with a Maxwell and Poynting explanation for everything.

[SandyCox]

Even though there will be some current flowing immediately, it will take some time before the lamp is fully lit, and the turning on will exhibit interesting stepwise increase of the light intensity.

This stepwise behavior is seen also in some oscilloscope pictures above.

Thank's Lapi. The theretical analysis I posted on p 19 confirms your simulation.

Sandy

[adx]

@Bud: The magnetic field at DC will go straight through a copper plate. The electric field AKA voltage difference will crowd into the gap. From this time of night I can't see how that makes you wrong. The bulk of the magnetic field will be in a place with no electric field.

But does the current create the magnetic field, or does the magnetic field create the current?

I don't know, because I think my brain actually hurts. Or at least the parts of it capable of feeling pain.

I thought I was pretty sure lastnight that the field follows from the charges moving if there are mobile charges. But penning a description for far too long now, and I started thinking something else, about photons creating the magnetic field and aspects of spacetime - a string of thought experiments heading too far off into science fiction to post without checking some stuff. Oh my lobes, my lobes. I've got the horrible feeling I'm going to have to do some maths for the first time in my life. The field solver in my head learned from observation, it is a neural network after all, not a fortran compiler. Or maybe it is, it's just a coprocessor, so I don't really know!

I still wonder what happens to the Poynting vector deleted when a magnetic field extends into a copper plate at DC.

[HuronKing]

"The Poynting Vector is pointless."

Please, kindly, toss all your coax cables out the window then.

Apparently you missed the context.  I was referring to steady-state DC circuits exclusively, which ironically I often use coax cables for--but that's a different issue.  And I didn't say that they (Poynting vectors) can't be calculated, drawn or that they somehow don't apply--I said that they are poyntless in that they serve no purpose other than to give you the smug satisfaction that you are above all the other heathens because you somehow "know what is really going on".

Anyone who brings up poynting vectors in DC circuit theory will be laughed out of any engineering classroom or lab.

You say that but I teach DC and AC circuit theory at my university alma mater, so...   

I wonder how many EEs, as opposed to physicists, have had a practical use for directly using Poynting vectors or Maxwell's equations since leaving university? Sure we all know the right- and left-hand rules, and an RF engineer might well have use them indirectly when using an EM or antenna modelling package, put I doubt most EEs will have touched them, or have had a need to do so directly, since leaving the classroom.

That's not the idea though even if you're right and it is a minority who ever do an actual Poynting Vector cross product. However, if I ask an engineer, 'where is the energy in the coax cable?' and they respond 'in the wire' then I know they don't actually understand how it works (why do different dielectrics create different characteristic impedances?). I mean, I am in awe of Heaviside's insight into the Poynting Vector and his DIRECT application of Maxwell's Equations to inventing the coaxial cable:
https://www.microwaves101.com/encyclopedias/multi-dielectric-coax

"But my model is good enough for what I want to do! Who cares?" (things I've heard my students say)

Maybe, but as an engineering educator, I have NO idea what my students will be doing when they leave school. Maybe all they'll do is load calculations for residential construction - or maybe they'll become a top-notch RF engineer. I don't know. My job as an educator (and as a working professional mentoring interns) is to do my best to ensure they have the correct physics understanding of the underlying phenomena so they can apply it to ANY EM problem and arrive at the correct answer. They can make their own shortcuts and tools with this knowledge.

I'm doing a disservice to the profession of engineering if I handwave away Maxwell and say "well you'll never actually need this so I'm not going to show you where the shortcut comes from but just give you the shortcut..." and substitute the rote intuition of limited models applied to specific conditions for the actual physical theory whose simplifications have created the models.

Another good example of this is voltage transformation in a transformer. Yes - the turns ratio for voltage transformation is described by a simple fraction, but getting that fraction from Faraday's Law is quite interesting and provides tremendous insight into how AC asynchronous induction motors work (I make it a requirement in the class I teach). Will anyone actually be doing vector calculus over and over again? No, of course not - but they'll be well-suited to be expert engineers in knowing when the model works and when it doesn't.

There are reasons this theoretical knowledge gets tested to become a professional licensed engineer.

[SandyCox]

Nobody here is denying that the physics isn't right. We are pointing out that there are ALSO ways that engineers look at these sorts of problems, and for good reason. And it also gives people ANOTHER WAY to look at the problem and get the same answer. That's a good thing. Not everyone is best served with a Maxwell and Poynting explanation for everything.

From an engineering perspective, it is more important to understand the role of impedance matching. Without proper matching, the light bulb might fail due to overvoltage after a few seconds.

For example, the attached graph shows the voltage across the bulb if the DC battery voltage is 220V and we use a 5W bulb.

Sandy

[adx]

I've said in other discussions that there is absolutely no need to teach electronics at any level with exemplar circuits that do not work properly, or would be totally impractical, because it is always feasible--and better in the long run--to do a bit of extra work and provide a realistic, practical example.  The same goes for this case.

What is more practical than a battery, a switch, wires and a lamp?

A battery, switch, wires, and lamp that actually work.

I'm not saying they wouldn't work, or should have been made smaller (I wrote something suggesting this a day or 2 ago but ran out of time to post it, along the lines of a 15km line of wire 1mm apart to trip the mental transmission line detector), or it wasn't a good problem. Just that the fact it doesn't work exposes a whole lot of untestable assumptions. People are wildly confused over whether it is a thought experiment, about the "any current" will light the lamp, conductivity of the ground, whether coax would be conceptually equivalent, and so on.

I don't have a problem with it in this case, but I've had a little too much "assume" in my education, along with fellow students (mainly earlier school), so this concept triggered me.

[Sredni]

"The Poynting Vector is pointless."

Please, kindly, toss all your coax cables out the window then.

Apparently you missed the context.  I was referring to steady-state DC circuits exclusively, which ironically I often use coax cables for--but that's a different issue.  And I didn't say that they (Poynting vectors) can't be calculated, drawn or that they somehow don't apply--I said that they are poyntless in that they serve no purpose other than to give you the smug satisfaction that you are above all the other heathens because you somehow "know what is really going on".

Anyone who brings up poynting vectors in DC circuit theory will be laughed out of any engineering classroom or lab.

Must have been one of the outtakes of "Idiocracy" that are on the deluxe edition of the DVD.
They laughed at Sommerfeld, Jackson, Kraus...

You know who would be laughed out of an engineering classroom in any decent university? The guy who thinks that at DC the Poynting vector is directed toward the battery, and also thinks the skin effect has anything to do with that direction reversal.

The first and most important thing an engineer should learn is: know the limits of your models.
You and Mehdi think the effect of the field propagating from the switch can be modeled by a transmission line that extends in the perpendicular direction? Think again.
What is modeled in a transmission line? What components are used to model a transmission line with distributed parameters? Do those elements, taken by themselves, model the propagation of EM fields along their extension? Or are they lumped elements?
Do you think a lumped capacitor in SPICE will model the delay it takes for the electric field to propagate from one plate to another?
Think again.

[bdunham7]

Modeled with what model? With the model of your misconception? That's precisely the point of Derek's video: show that your model doesn't work.

Which model of mine 'doesn't work' ?? 

Someone here in this thread reproduced his experiment using shorter wires, pulse generators and an oscilloscope capable of detecting picoseconds.

No, they used a scaled-down experiment that is similar but not identical.  And I wish they'd held off until you had actually stated how you expected the circuit to respond so we could compare your results with the pretty much correct results from the heathens using LT-Spice and so on (the stepped reflections). 

What is more practical than a battery, a switch, wires and a lamp?

With superconducting wires and a lamp that lights at any current level?

His experiment is falsifiable, because you can reproduce it in dimensions other than wires extending 300.000 km. He just chose those dimensions because it gives round numbers like 1 second, 2 seconds, etc. Time delays that are intuitive to a non specialized audience.

Yes, the actual phenomenon would be dry and boring so he spiced it up for the 'general audience'.