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_....

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

I am not going to read this whole thing as I am late to the party so please forgive me if I repeat something already said

Almarg, you are usually spot one but missed one here.

The electromagnetic wave is the audio signal. There is no electromagnetic wave in the power cord or in the fuse where the power cord enters the amp.

The energy in the incoming power is indeed an electromagnetic wave like all AC signals. How can a 60 Hz "audio" signal be EM and a 60 Hz line signal not be? Plug your speaker into the wall outlet and you will hear a very loud 60 Hz for a brief period of time.

Earlier someone gave a flawed analogy about measurements. Stating that since capacitors of the same value and precision sounded different there must be more to this than just measurements. The flaw in that argument is that caps have more parameters than just value and precision. Leakage current, effective series resistance, some amount of inductance causing them to be resonant at some frequency, temperature coefficient, type of dielectric, etc. I propose that if all parameters were exactly the same then they would sound the same which makes the original supposition invalid.

The misconception that electrons are flowing down the wire from source to load is very firmly implanted in many minds. They were taught using the very flawed analogy that electrons flowing through a wire is like water flowing through a hose . "Mr. Smith taught me that in 8th grade so it must be correct.”

It is very difficult if not impossible for many (most?) to conceptualize energy transfer but very easy to think of electrons flowing like water so they are stuck in a world where cables can’t be directional because electrons flow one way and then the other in AC. I struggled with that when the concept was introduced to me in Freshmen physics. I couldn’t understand how there could be a power plant a thousand miles away and electrons were making trips back and forth 60 times a second. Of course they weren’t. Energy was flowing from the power plant to my house in the form of an EM wave, not electrons.

The flowing electron myth can be easily debunked if you can wrap your head around an electromagnetic wave. Light, what we call microwaves, radio waves, etc. are all the same thing just at different frequencies. Audio signals are the same thing at very low frequencies. If the frequency is high enough these waves travel easily through air or a vacuum with no associated movement of electrons. At audio frequencies they will too just not very efficiently so it is easier to guide them where we want them to go since they will follow a wire. The resulting vibration of electrons with AC or the very slow migration of electrons with DC is an effect caused by the wave, and that is what trips many up. They think the movement of electrons is the cause when it is the effect, the movement of energy is the cause. Again, if the energy will travel in the absence of electrons (vacuum) then electrons are not the cause. While I can imagine an AC wave like light traveling  I admit I do have trouble conceptualizing how DC energy "flows" so I just accept that it does. 

So can wires be directional? If they are not symmetrical it is easy to see why they would be. Ralph gave the example of asymmetry in a cable where the ground is connected on one end only. Cables with termination networks like MIT would surely be directional. If the way the wire is drawn results in an asymmetrical crystal structure I suppose there could be an effect. Now if a cable is perfectly symmetrical it is hard to see how it could be but since the energy always flows from source to load maybe this somehow conditions the wire so maybe, would explain the burn in effect that many adhere to. At the end of the day I am in the camp of just try it. If you hear it then it is real.

Thanks, Herman, for your characteristically excellent input, which like many posts you have made in the past commands a great deal of respect in my book.

To be sure it’s clear, the statement that is quoted near the beginning of your post was made by Geoff. The reference to me which appears just above the quote might give some a different impression. And of course I agree that the quoted statement is incorrect.

Best regards,
-- Al