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In Reply to: RE: GargOyle... Hows wire direction shaping up for you ?? posted by cpotl on October 09, 2015 at 17:44:57
Thanks for clearing that up with facts instead of faith.
Follow Ups:
Can I throw this into the discussion.
https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part6/page2.html
"In fact, we can now reveal that it is the electromagnetic fields that surround metal wires that actually carry the signal energy. Here we can examine three standard cases, starting with one that looks like the 'house to house' system we looked at earlier. In each case it turns out to be the product of that carries the power and the electrons are almost irrelevant except as a convenient place to 'pin' or 'control' the fields. The wires (more precisely, the electrons inside the wires) act to guide the fields, but it is the fields that do the real work! "
"In each case it turns out to be the product of that carries the power and the electrons are almost irrelevant except as a convenient place to 'pin' or 'control' the fields"
It seems to me he is setting up a straw man and then knocking him down. No one would ever have suggested that the energy transfer was mediated by the mechanical kinetic energy associated with the drift velocity of the electrons, and indeed, as he observes, that is a really tiny quantity.
It's not my field, but I think I could track down a good reference book on the theory of electrical conductivity in metals. I'd be happy to try to find it, if you are interested.
One has to keep in mind some very different regimes when discussing electrical energy transfer down wires. For DC, I would recommend that you try the calculation of the Poynting flux, which your reference speaks of. I think you would find that it just reproduced the ohmic power dissipation, due to resistive losses in the wire. It's a nice calculation, and an equivalent way of seeing the same thing you see in a standard calculation using a model for the electronic conduction in the metal. For the microscopic details of the conduction in the metal, you would need the standard theory, involving conduction bands, Fermi levels, etc. Interestingly, the classical theory, as in the Drude model, has substantial deficiencies, and quantum mechanics is really needed to get a satisfactory model that matches the experimental data, such as temperature dependence and so on.
By the time you get to high enough frequencies (or long enough stretches of conductor), you would be approaching the regime where the theory of transmission lines would become appropriate. Now, it becomes more like a discussion of electromagnetic waves.
But for low frequencies such as in audio amplifiers, and even more so for the 60Hz frequency involved in the mains power cable, electromagnetic waves are pretty much irrelevant, I think. It is really just a situation where there are slowly-varying currents and voltages, and the steady-state DC model, with a sort of adiabatic time dependence, is quite sufficient.
The mechanisms involved in the electrical conductivity in metals are quite subtle, and it is a beautiful and very well-studied subject. There is nothing in the standard picture described in the physics literature that is going to be challenged by phenomena encountered in a home stereo system, I think. Scientists working in that field are involved in much more subtle investigations than that.
Chris
Thanks
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