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

--- Quote from: penfold on March 15, 2022, 09:02:02 am ---
--- Quote from: aetherist on March 15, 2022, 02:32:49 am ---[...]But u make it sound like wiki didnt mention the Newton's Cradle at all. Newton's Cradle is nothing but mechanical. They might not mention bumping, but they mention collision strike etc.[...]
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There is the added complication of it being a 3-dimensional... and added complexity of the stationary lattice of positive ions. In the nano-meter and pico-meter scale, the inverse square law makes for almost unimaginable/unrelatable force to mass ratios and impossibly high numbers of involved particles (~10^28 for a small amount of copper). Naturally, to deal with the 'movement of electrons' as a field in a conventional sense, there's no real scope to find exact solutions as one could in a diabolical multi-body problem, there are thermal fluctuations and random lattice defects, so only a statistical representation is possible... luckily for such a huge number of particles, it averages out quite nicely. The other thing with the fixed lattice is that relatively minor variation in charge distribution produces a massive 'rectifying' force, and most likely below the amount caused by random thermal fluctuations.

--- Quote from: aetherist on March 15, 2022, 02:32:49 am ---[...]There will be a visible wavefront of moving discs. The speed of the wavefront will be much faster than the speed of disc1.
Actually the wavefront will move at almost the speed of light. But this will involve microscopic movement of the discs.
The larger movements/wavefront more obvious to the eye would be much slower than the speed of light.
And here we come back to the fact that the wavefront of drifting electrons in a copper wire must be much slower than the needed speed of light.
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We know that fields exist outside the conductor, that the magnitudes of those fields and their vector product is proportional to energy flow. We know that the propagation speed of the E and B fields is affected by the presence of and transfer of momentum to electrons and dielectric properties that we call inductance and capacitance. We also know that the transfer of energy from one point in the circuit to another doesn't rely on a continuous uniform current density along the path of the wire... why must the speed of electrons match the speed of energy?
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I am fairly sure that i/we have already looked at the catastrophe of old (electron) electricity, ie that drifting electrons can't possibly be responsible for the speed of electricity being nearly the speed of light.
If everyone agrees that drifting electrons don’t play a part in the speed of electricity then that removes that catastrophe (but it might of course create others).
But i am pretty sure that everyone can't agree that electron to electron bumping duznt play a part in the speed of electricity. Which puzzles me. Everyone seems to agree that the electric energy is in the Poynting Field, but then some kind of postulate is added that the electron to electron bumping wavefront needs to feed back some kind of magnetic component or something.

I didn’t say that the speed of electrons must match the speed of energy, but i did say that many days ago on this thread. I said that the speed of the wavefront can't be more than the speed of the electrons. If u think about it u can see that is true for every kind of wavefront caused by particles. If the particles are say bricks placed hard up to each other then that law changes so that it says that the speed of the wavefront cant be more than the speed of a part of each brick.

And i remember that i pointed out that the catastrophe is made worse when u consider the fact that electron to electron bumping must act along a traject that is much longer that the length of the wire, ie electrons have to go over & around atoms & crystals etc, which might double the distance.
bsfeechannel:
The only catastrophe here is your huge ignorance of electromagnetism. No big deal. Most people don't understand it anyway. But if you really want to understand it, you have to first get rid of all the analogies you are used to. Trust me.
adx:

--- Quote from: aetherist on March 15, 2022, 11:12:49 am ---I didn’t say that the speed of electrons must match the speed of energy, but i did say that many days ago on this thread. I said that the speed of the wavefront can't be more than the speed of the electrons. If u think about it u can see that is true for every kind of wavefront caused by particles. If the particles are say bricks placed hard up to each other then that law changes so that it says that the speed of the wavefront cant be more than the speed of a part of each brick.

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Have a steel wire 100m long connected at the far end to a small brick. At t=0 start pulling the near end of the wire at 0.1m/s. (If you want, allow it to ramp up over 100ms to avoid infinite acceleration.) The wavefront travels along the wire at say 5km/s, so it starts moving the brick at t=~20ms and up to full speed at t=~120ms.

What particles in this system are moving at or more than 5km/s?
penfold:

--- Quote from: aetherist on March 15, 2022, 11:12:49 am ---[...]
I am fairly sure that i/we have already looked at the catastrophe of old (electron) electricity, ie that drifting electrons can't possibly be responsible for the speed of electricity being nearly the speed of light.
If everyone agrees that drifting electrons don’t play a part in the speed of electricity then that removes that catastrophe (but it might of course create others).
But i am pretty sure that everyone can't agree that electron to electron bumping duznt play a part in the speed of electricity. Which puzzles me.
[...]

--- End quote ---

Drifting electrons and bumping... I think I see your point now, with mean free paths ~10^-9 m, collision rates ~10^12 Hz should mean velocities circa 10^3 m/s: much slower than the e-field, therefore, bumping collisions don't convey momentum fast enough? And if they did they couldn't also transfer energy to the lattice in ohmic losses?

In a non-rigorous sense, the E-field (internal to the conductor) due to compression and rarefaction in an electron gas can travel fast... (I don't have the numbers to hand) and electric fields externally can also travel fast and can travel ahead of the electron wave-front, but also bare in mind that it's just a big set of differential equations so nothing is just happening without cause and consequence causing further consequence. The weakness in such a simplistic explanation is that it doesn't cover even a fraction of what's going on inside a metal and you very quickly need to either back-track into viewing the current as a smooth J component in Maxwell or proceed down the mystical path of quantum.
aetherist:

--- Quote from: adx on March 15, 2022, 12:10:59 pm ---
--- Quote from: aetherist on March 15, 2022, 11:12:49 am ---I didn’t say that the speed of electrons must match the speed of energy, but i did say that many days ago on this thread. I said that the speed of the wavefront can't be more than the speed of the electrons. If u think about it u can see that is true for every kind of wavefront caused by particles. If the particles are say bricks placed hard up to each other then that law changes so that it says that the speed of the wavefront cant be more than the speed of a part of each brick.
--- End quote ---
Have a steel wire 100m long connected at the far end to a small brick. At t=0 start pulling the near end of the wire at 0.1m/s. (If you want, allow it to ramp up over 100ms to avoid infinite acceleration.) The wavefront travels along the wire at say 5km/s, so it starts moving the brick at t=~20ms and up to full speed at t=~120ms.

What particles in this system are moving at or more than 5km/s?
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Tricky.  I think that there is no proper wavefront here, at least not of the sound kind of wavefront.
There will be the usual microscopic wavefront that propagates at nearly the speed of light in the steel.
And after that there will be a gradual increasing force pulling on the brick. This force (forces) could be calculated, using mass & Young's Modulus. But not needing any info re the speed of sound in Fe.
The brick might reach its max speed at say 5 seconds. This would  suggest some kind of wavefront propagating at 20 m/s (L of wire is 100 m). It duznt need 5 km/s.
The brick's max speed might reach say 0.2 m/s. And some bits of wire will reach a max speed of 0.2 m/s.

The answer here needs to tell us what a proper wavefront is & isnt. I think that a proper wavefront involves a shockfront effect (ie sound). A shockfront involves a vibrational deformation of the lattice (rather than a gradual accel plus gradual one-way deformation).
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