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

--- Quote from: electrodacus on June 28, 2022, 06:09:22 pm ---
--- Quote from: rfeecs on June 28, 2022, 05:30:21 pm ---The electron would repel the electrons of the copper box.  So the inside of the box would have a positive surface charge and the outside would have a negative surface charge.  This results in a force on the electron, attracting it to the box.

In general, charged objects are attracted to neutral objects.

--- End quote ---

He used the electron just as an indication of an electric field inside the box induced by the two charged external plates. It is a theoretical example where electron is exactly in the middle of the box.
In his example there will be higher density of electrons on the top side of the box than on the bottom side but there will be no electric field inside the box if we ignore/remove that electron from the middle of the box.


Sorry I do not remember if  you express your opinion. Is the electrical energy flowing through wire or outside the wire?

--- End quote ---

How does an antenna get energy to couple to the receiver?
SiliconWizard:
*Invokes Tesla*

Nikola, forgive them, for they do not know what they are doing. ::)
electrodacus:

--- Quote from: Alex Eisenhut on June 28, 2022, 06:28:48 pm ---
How does an antenna get energy to couple to the receiver?

--- End quote ---

Transmitter antenna is one plate of the capacitor and the receiver is the the other plate of the same capacitor.
A simple AM transmission will be a capacitor between ground (earth) and the anthena (a wire above the ground that is charged and discharged relative to earth).
You can have as many receiving antennas as you want around the transmit antenna and they will form small capacitors with the current loop closing trough earth/ground.
You charge and discharge capacitors.
Try and supply DC to the transmit antenna and you will not get anything on the receiver.
Naej:

--- Quote from: Sredni on June 27, 2022, 08:34:14 am ---
--- 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?

--- End quote ---
Derek only asked a question on the transient, hence my comment.
If you have 300000 km of wire with a DC resistance of 1 µohm, let's say you have a wire radius of 1 cm so the resistivity is 10^-18 Ohm m (1 billionth copper's).
The skin depth at 0.1 Hz is 1.6 µm, which definitely looks like surface current no?
After a few years (~ nHz) the current will penetrate the core of the wire.

--- Quote from: Sredni on June 27, 2022, 08:34:14 am ---
--- 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.

--- End quote ---
Yes. But you wouldn't say E=B=0 in an extremely good conductor?
electrodacus:

--- Quote from: Naej on June 28, 2022, 10:12:36 pm ---Derek only asked a question on the transient, hence my comment.
If you have 300000 km of wire with a DC resistance of 1 µohm, let's say you have a wire radius of 1 cm so the resistivity is 10^-18 Ohm m (1 billionth copper's).
The skin depth at 0.1 Hz is 1.6 µm, which definitely looks like surface current no?
After a few years (~ nHz) the current will penetrate the core of the wire.

--- End quote ---

There is only proximity effect due to initial transient but even with 300000km of wire you have just DC after a few seconds so current flows uniformly through the entire section of the wire with very small proximity effect due to small voltage drop on the transmission line.

For example Derek used a pipe in his experiment and he could have calculated the wire resistance by just measuring the voltage and current (current that will have been constant after just a fraction of a second in his experimental setup).
If he will have used a solid bar or copper and measured the voltage drop he will have seen a direct correlation with increase in cross section area meaning current flows uniformly inside the conductor not on the surface.

And no matter if you have DC or AC in Derek's circuit the energy will always flow through the conductor. While with high frequency AC the resistive loss of the transmission line will increase the current still flows inside the conductor thus energy is still delivered through the conductor.
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