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Electroboom: How Right IS Veritasium?! Don't Electrons Push Each Other??
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electrodacus:

--- Quote from: Sredni on June 24, 2022, 06:49:24 am ---Why you people keep turning simplifications into overcomplications?
Both in Derek's and Lewin's problems the term superconductor is used to avoid the unnecessary complication of losses in the cable, in order to focus only on the phenomena of interest. What's next? A thermodynamic analysis on how it is possible to maintain cryogenic temperatures without altering the fields in the coil? Or a discussion of why Derek did not take into account the temperature profile of the atmosphere and the effect of Van Alllen's (or was it Van Halen?) belt when his cable reach halfway to the moon?

--- End quote ---

The one that overcomplicates things is you.

Questions is simplified to:  Is the electric current traveling through the wire or outside the wire?
If you agree with everybody else "stream of charged particles" then that can only happen inside the conductor in Derek's experiment.
I need to specify Derek's experiment because you can have a stream of electrons even though vacuum like I showed for the vacuum diode or cathode ray tube but that is not happening at 20V with 1m between the wires.
 
Electrical power is the product of electrical current and electrical potential and electrical energy is electrical power integrated over time.
Since you have electrical current in the wire you have electrical energy traveling through the wire.
Also there is no electrical current in that 1m air gap thus there is no electrical energy transferred through that air gap.

In order for you or anyone else to claim that energy travels outside the wire you need to prove that electrical current travels outside the wire and that means charge particles traveling in that 1m gap between the source and the load.
aetherist:

--- Quote from: aetherist on June 24, 2022, 11:46:33 am ---
--- Quote from: Sredni on June 22, 2022, 07:15:36 pm ---
--- Quote from: rfeecs on June 22, 2022, 06:45:53 pm ---
--- Quote from: Sredni on June 22, 2022, 04:53:29 pm ---I was talking about the surface charge: the excess electrons or lack thereof that - along with the original external field generated by the battery - shape the electric field inside the conductor in such a way that it be directed along the conductor axis and will have a magnitude that satisfies Ohm's law in its local form.
--- End quote ---
So what happens with a superconducting wire?  Presumably the surface charges make the field inside the wire zero.  So what makes the current go?
--- End quote ---
Ah. Superconductors are quantum beasts. (Well, technically even ordinary conduction requires quantum theory to give quantitative agreement).
If we stay in the realm of classical ED, we can consider a perfect conductor as the limit of a resistive conductor for sigma->infinity. You need an infinitesimally small field to make the electrons move. But it can get tricky. Last year (?) Lewin posted a problem with a superconducting ring in a changing magnetic field. Basically what we call Lewin's ring but without resistors. What will happen? Only two people, among all those who were exposed to the problem (and they included several physics professors to which Lewin had emailed the problem) gave the correct solution. One is a professor in a University in Switzerland (IIRC) and the other is George Hniatuk (he has a youtube channel).

The solution is: no current inside the superconducting ring.

I had it wrong: my initial assumption was that the current would rise so rapidly - being a superconductor - that the small self inductance of the ring would act as a current limiter.  Then I saw George Hniatuk's comment (Nope. No current inside) - and knowing how he knows EM - I realized he was right. (Math and Physics are different - in math you can create the induced electric field magically inside the superconductor, in physics you must justify its presence there. How do you place it in? Surface charge will redistribute in such a way as to prevent it from entering the ring).

But this is not the reason I am telling you this. In the video (I will add a link tomorrow, now I need to sleep), or in the comments, Lewin made a very interesting statement. That to initiate a current in a superconducting ring you need... a resistor. You start your magnetic mumbo jumbo with the resistor inserted - and it's the field in the resistor that makes the electron go - once in the superconducting material they continue 'by inertia', and only after the current is established, you switch to a full superconducting ring.

Pretty crazy, uh?
--- End quote ---
Komplete krapp. Lewin is an idiot.
My electon electricity is on the surface of the conductor. Game over.

--- End quote ---
Another thing. Lewin mentions a correct solution. There are 2 kinds of correct solution.
(1) A theoretically correct theoretical solution. Lewins has embraced this with zero apology.
(2) A practically correct solution based on measurements (with a minimal amount of theory & assumptions).
(1) Is a faux solution, little better than arguing about how many angels can dance on a needle.
(2) Is a true solution, limited by the minimal amount of theory needed, & limited by the practical shortcomings & assumptions of the experiment design & measurements.
Lewins duznt seem to know the difference tween (1) & (2).
Praps he can do a youtube re the theoretical colour of Unicorn poo.
Sredni:

--- Quote from: Naej on June 24, 2022, 09:41:07 am ---Derek circuit is not at DC (it's a mind trick), the effect he talks about is at ~1m wavelength (and you can see it on the oscilloscope).
The reason why I used 300 Mhz in a 0.1 mm wire is to get a similar ratio between current depth and wire radius in a copper and superconductor wire.

--- End quote ---

Derek set out to show that energy is in the fields for a DC circuit. He uses the initial transient to drive his point home because the energy that reaches the load before the time length/c cannot come from the cables.
Are you suggesting that even when the transient has subsided the only current in the cable is that on the surface? My take is that Derek uses the term superconductor to mean "let's not consider the resistance in the wires" and not "let's use an exotic material cooled with liquid helium all the way to the Moon".

What if the cables had a total resistance for their entire lenght of 1 microohm? Would you still consider the current as only surface current, after say 10 seconds since the switch is closed?


--- Quote ---Definitely not in Lewin's. He says E=B=0 inside the superconductor, one of the most well-known fact (or "fact") about them.
If Lewin wanted, he could have taken a wire with a 50 cm thick copper wire, or 5 cm steel wire with a more reasonable size so that it works at 1Hz.
It is, after all, a thought experiment.

--- End quote ---

As far as the coil or the magnet is moving, I don't see a difference between the behavior of a perfect conductor and a superconductor. The difference come with the static field, but a static B field won't be able to induce a current. So, if the induced electric field had no way to penetrate the perfect conductor (because of the surface current killing it in the cradle), Lewin's experiment should lead to the same result both for perfect conductors and superconductors.
I still think Lewin is using the term superconductor to mean "no resistance whatsoever in the material" and not as something his JEE students should elaborate on.
electrodacus:

--- Quote from: Sredni on June 27, 2022, 08:34:14 am ---
Derek set out to show that energy is in the fields for a DC circuit. He uses the initial transient to drive his point home because the energy that reaches the load before the time length/c cannot come from the cables.
Are you suggesting that even when the transient has subsided the only current in the cable is that on the surface? My take is that Derek uses the term superconductor to mean "let's not consider the resistance in the wires" and not "let's use an exotic material cooled with liquid helium all the way to the Moon".

What if the cables had a total resistance for their entire lenght of 1 microohm? Would you still consider the current as only surface current, after say 10 seconds since the switch is closed?

--- End quote ---

Derek's claim is that "energy doesn't travel through wire" and this is a direct quote.
At DC steady state the electric current that is defined as a stream of electrons flows uniformly through the entire cross section of the conductor.
Since electric current travels through the wire it means energy travels through the wire.
During the transient part all current flow is still in the wire is just that part of the current charges the line capacitance and part of the current is lost on the Lamp as lamp is between two capacitors that are being charged.
 



--- Quote from: Sredni on June 27, 2022, 08:34:14 am ---
As far as the coil or the magnet is moving, I don't see a difference between the behavior of a perfect conductor and a superconductor. The difference come with the static field, but a static B field won't be able to induce a current. So, if the induced electric field had no way to penetrate the perfect conductor (because of the surface current killing it in the cradle), Lewin's experiment should lead to the same result both for perfect conductors and superconductors.
I still think Lewin is using the term superconductor to mean "no resistance whatsoever in the material" and not as something his JEE students should elaborate on.

--- End quote ---

With no resistance in a conductor the current flow induced by the changing magnetic field will remain there.
So once you induce a current flow that will be permanent as without resistance to current flow there is nothing to stop it.
aetherist:
Sredni  Naej  electrodacus & Everybody & Co.
What is a wire that has zero resistance?
What is a wire that is a perfect conductor?
What is a wire that is a superconductor?
What are the differences?

Here my meaning is what are the critical electrical properties.
The answers or definitions might i suppose be of an entirely or partly gedanken nature.
This would be in the context of Lewin's gedanken, & praps Veritasium's gedanken – ie short & sweet & simple.

I have given this some thort over the past 6 months.
A warning --                              "O, that way madness lies; let me shun that;  No more of that”
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