Directionality of wire

If somebody is interested in the math of electrical energy flow in cables, this is a good article in Am. J. Phys. (it's possible to read the paper without following all the math):

http://depa.fquim.unam.mx/amyd/archivero/El_flujo_de_energia_de_una_bateria_a_otros_elementos_de_un_... 

sfroyen
geoffkait: There is no law saying photons can’t travel in copper. In fact it’s the physical non symmetry of the copper ITSELF that gives rise to directionality. Hel-loo!

Indeed there is. The laws are called Maxwell’s equations and were published in the 1860s. They are fully relativistic and form the basis for all electric, optical and radio technologies. In fact they are also used to calculate the skin-effect. As I stated above, any asymmetry in the copper can only affect the electron motion -- not the photons (electromagnetic fields and photons are one and the same).

>>>>as I already said the skin effect is simply that higher frequencies travel nearer to the outer surface of the conductor. And those frequencies are very high. Obviously, by inference, the lower the frequency the closer to the center of the conductor it will travel. How does that comport with the electromagnetic wave - the audio signal - traveling outside the conductor as you claim? Hint: it doesn’t.

If somebody is interested in the math of electrical energy flow in cables, this is a good article in Am. J. Phys. (it’s possible to read the paper without following all the math):

http://depa.fquim.unam.mx/amyd/archivero/El_flujo_de_energia_de_una_bateria_a_otros_elementos_de_un_....

That paper does not show that the electromagnetic field of the AUDIO SIGNAL travels outside the wire nor does it show that current travels outside the wire. What it shows is that *components* of the electromagnetic field can travel on the surface of the wire. We already know that a magnetic field induced by current traveling through wire and extends beyond the wire according to the right hand rule. (This is why it’s important to address the large magnetic fields produced by large transformers in audio systems with low frequency high permeability alloy.) The paper involves a battery connected to a wire so I’m not sure this paper even applies to an audio system. The paper also states there is energy INSIDE the wire and describes the mathematics of the electric field and magnetic field INSIDE the wire. See top of page 1.

Furthermore, take the case of the humble fuse in the amp where the power cord enters the amp. The fuse wire is designed to melt at a given temperature based on excessive current. That melting is produced by thermal energy of the current, no? The current must be traveling inside the wire per se, if the current energy were traveling outside the wire it would be dissipated into the surrounding air and structure of the fuse and beyond. So the whole idea of "energy" traveling outside the wire is pretty preposterous. Obviously there can be some components such as induced magnetic field outside the wire per se. Everybody knows that.

Geoffkait 8-5-2017
as I already said the skin effect is simply that higher frequencies travel nearer to the outer surface of the conductor. And those frequencies are very high. Obviously, by inference, the lower the frequency the closer to the center of the conductor it will travel. How does that comport with the electromagnetic wave - the audio signal - traveling outside the conductor as you claim? Hint: it doesn’t.

Actually, it does. See below.

Geoffkait 8-6-2017
Furthermore, take the case of the humble fuse in the amp where the power cord enters the amp. The fuse wire is designed to melt at a given temperature based on excessive current. That melting is produced by thermal energy of the current, no? The current must be traveling inside the wire per se, if the current energy were traveling outside the wire it would be dissipated into the surrounding air and structure of the fuse and beyond. So the whole idea of "energy" traveling outside the wire is pretty preposterous.

In the case of electrical signals (or AC power) that is being conducted via wires, "the current" consists of the movement of charge under the influence of an applied electric field (i.e., a voltage), and the carriers of that charge are electrons.

As we all agree the movement of individual electrons (the "drift velocity") is extremely slow. However as the electromagnetic wave propagates along a cable, at near light-speed, **different** electrons are caused to be in motion at different points. The very slow electron movement near the receiving end of the cable will be similar to the very slow electron movement near the sending end of the cable, except that its response to a voltage applied at the sending end will be delayed corresponding to the amount of time it takes the electromagnetic wave to propagate (at near light-speed) across the corresponding length.

The net movement of electrons at any given point along the cable will be in a direction corresponding to the +/- polarity of the signal at any given instant, at that given point. And the number of moving electrons will be proportional to the amount of current, and in fact is what constitutes "the current," which if excessive will blow a fuse that may be present. For example, one ampere of "current" is defined as the movement of one coulomb per second across any given cross-section of a conductor, and one coulomb corresponds to the charge of approximately 6.2 × 10^18 electrons.

Skin effect results in the moving charge carriers (electrons in this case) being distributed in a non-uniform manner within a cross-section of each of the two conductors. Such that the percentage of the total current that is conducted at a given depth within that cross section decreases with increasing depth. With the effect becoming greater as frequency increases, of course. The result, in effect, is an increase in overall resistance, which is very slight in the upper-most part of the audible frequency range, and becomes proportionately greater at higher frequencies.

Geoffkait 8-5-2017
But seriously, we already know the velocity of photons traveling through copper conductors (circa 70% speed of light in vacuum) and it’s consistent with the photons traveling through the metal conductor itself, NOT through the dielectric and NOT through air, which would be a much higher percentage of the speed of light in a vacuum, no? It’s the same situation for audio over copper wires in telephony, too. The velocity over copper wires in the telephone system is consistent with the signal traveling through copper itself. Electrons? They hardly move at all so we can ignore them.

The bottom line as I see it, based in part on the last sentence of your paragraph that I quoted just above, is that I suspect the underlying flaw in your reasoning, which leads you to conclude that the energy of an audio or other electrical signal is carried by photons travelling within a wire, is a misconception of how the near light-speed propagation of an electromagnetic wave and the very slow movement of charge carriers (i.e., electrons) within a conductor are interrelated. Again, slow moving electrons are "the current," and although as you’ve said the very fast moving electromagnetic wave can be considered to be "the signal," the two go hand in hand.

If you can find a seemingly credible reference which explicitly indicates that the energy of an electrical signal conducted via wires is carried within the conductors by photons, I will attempt to explain why it is either incorrect or is being misinterpreted.

Regards,
-- Al