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"Veritasium" (YT) - "The Big Misconception About Electricity" ?
SandyCox:
By looking closely at Example 11.3.1 of Haus and Melcher we can see that Veritasium is wrong. In this example, all the power is being transferred by the conductors. No power is transferred in the region outside the conductors. Haus and Melcher should have said "power seems to flow through the open space" instead of "power is seen to flow through the open space".
The power entering the washer from the voltage source is:
Pw = 2*pi*sigma*delta*V*V/ln(a/b)
By integrating the Poynting vector over the outer surface, we find that the power that is dissipated in the washer is:
Pw = 2*pi*sigma*delta*V*V/ln(a/b)
The power entering the rod from the voltage source is:
Pr = pi*b^2*sigma*V^2/L
By integrating the Poynting vector over the outer surface, we find that the power that is dissipated in the rod is:
Pr = pi*b^2*sigma*V^2/L
So all the power entering the washer from the voltage source is dissipated in the washer and all the power entering the rod from the voltage source is disspiated in the rod.
There is no power being transferred in the region between the washer and the rod.
Will someone please check my calulations?
adx:
--- Quote from: bsfeechannel on January 03, 2022, 04:57:42 am ---
--- Quote from: vad on January 02, 2022, 04:12:13 pm ---[I have a question though. Consider the following experiment. Let's take a rubidium laser, shine its beam through a beam splitter, then one of the beams goes through a thick copper plate to a detector A, and another beam goes through the air unobscured directly to a detector B (sea level, 25C air temperature, 30% relative humidity). Can I assume that the probability of a photon reaching detector A (the one behind the metal plate) would be 999999 times higher than probability of reaching detector B, considering the same Coulomb's law and QED?
PS. Simplified version of this experiment can be reproduced by every member of this forum with a flashlight and a frying pan.
--- End quote ---
Your simple experiment is so brilliant that the Poynting-haters didn't even realize it.
--- End quote ---
Strudel complete. One more.
I got A and B backwards again. The copper block is missing the transverse m return path. Try cutting a slot in it (so you can see through your screen or at least to the VESA mounting pad, use the laser, but remember to remove a few km of optical length from it or at least turn it down afterwards, and check the detectors and beamsplitter for holes and rubidium fume). While at it, focus the laser around the entry to the block, so the beam diverges quite a bit. Make that plate longer (thicker) for good measure, move the detectors away and or check for copper intrusion this time (blame the instructions).
Now measure the intensit probability of measuring a photon at A and B. Frequency is a bit high for a DC circuit, but I'll accept some energy in the space between the 'wires'.
rfeecs:
--- Quote from: SandyCox on January 03, 2022, 03:40:10 pm ---
So all the power entering the washer from the voltage source is dissipated in the washer and all the power entering the rod from the voltage source is disspiated in the rod.
There is no power being transferred in the region between the washer and the rod.
--- End quote ---
You cannot conclude that from your calculation. It could be that power is exiting the washer and flowing into space (into the fields) and the same amount of power is flowing into the rod from the space (the fields) around it.
There is no double counting of power. Both views are equally valid in terms of conservation of energy.
But the "alternative" approach is only valid for DC. Using the Poynting vector is valid for all cases.
bdunham7:
--- Quote from: rfeecs on January 03, 2022, 05:44:29 pm ---You cannot conclude that from your calculation. It could be that power is exiting the washer and flowing into space (into the fields) and the same amount of power is flowing into the rod from the space (the fields) around it.
There is no double counting of power. Both views are equally valid in terms of conservation of energy.
But the "alternative" approach is only valid for DC. Using the Poynting vector is valid for all cases.
--- End quote ---
Poynting's Theorem, of course, is fully falsifiable and easily proven correct for all cases. I'm beginning to think this debate over the significance of the Poynting vector itself (as a 'true statement of what really happens' or 'proof that the energy flows in the fields through free space') is actually not resolvable because it is not falsifiable.
It can be difficult to rebut a claim that a mathematical model represents reality simply because it accurately predicts the result. In an earlier discussion it was stated that you could consider a 9-volt battery connected to a 300R twin-lead wire (open at the end) to be a transmission line with 30mA of continuous current outbound with an equal 30mA being continuously reflected. The math works for an ideal circuit and may be useful for solving certain problems, but I don't think anyone really thinks that the math reflects 'the real situation' or 'what is really going on'. And lets not even discuss whether imaginary cancelling currents would have parasitic losses or not.
So back to the Poynting vector. What does it mean to say that an arrow on a diagram represent power flow density in W/m2? Specifically, in the classic battery/wires/load rectangle there is a Poynting vector poynting directly away from the load on the outer side of the battery. Many diagrams conveniently omit it, Derek's video shows it but just truncates it without explaining its meaning. What does that arrow represent? Is it something tangible that can be measured, used, interfered with, etc? If I say that it is just a mathematical result (from two actual physical manifestations, E and B) that has no corresponding manifestation of its own in reality, just like the imaginary currents in the open transmission line above, can you counter that?
bdunham7:
--- Quote from: bsfeechannel on January 03, 2022, 04:57:42 am ---Your simple experiment is so brilliant that the Poynting-haters didn't even realize it.
--- End quote ---
Yes, we're all idiots. So please explain the brilliance of this experiment to us. Make sure to throw in the concepts of localization and the interaction between photon and a conductor.
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