Is AC energy really transferred as EM wave?

[Biocool]

In an AC circuit, say, the transmission of energy from your power generating station to your home, the electrons in the wires in the generator probably never make it to your home, they just oscillate back and forwards over a very short distance at 50 Hz/ 60Hz (depending where your are from) As they oscillate back and forwards, they undergo acceleration during each half cycle and its this cycling (oscillation) that generates the EM wave that I said above.
The energy is transmitted along the outside of the cable ( transmission line) via the EM wave

Ok. Suppose we have direct current in a solid conductor. But even in the case of d.c. electrons does not move with constant velocity because they interact with crystall lattice. So they should emit energy in the form of EM waves. Does electrons emit EM waves during their movenment in conductors? What is the magnitude of the energy loss?

 

[sophiecentaur]

in the case of d.c. electrons does not move with constant velocity

There is a vast range of velocities because the conduction electrons are in random motion, the average drift velocity is typically only a mm or so per second. For AC of any significant frequency, the actual displacement is incredibly small. So electron movement is really not a good way to discuss electric current.
I could suggest that the noise energy due to random electron movement is what you're probably looking for. It's always there in any electronic component.

 

[jartsa]

"Is just"? There is a world of difference between two parallel wires and a single, thicker wire. The propagation of an EM wave over a conductor (E field, nominally transverse) is actually not transverse. There is a slight forward tilt to the wave front, due to losses in the conductor. A number of insulated wires or layers could not support or explain this phenomenon. Your model is flawed, I'm afraid.

Well, maybe I should have said: "let us model the skin effect in a thick 60 Hz AC power wire by many thin parallel wires", instead of "thick wire is just many thin wires".

 

[jartsa]

Ok. Suppose we have direct current in a solid conductor. But even in the case of d.c. electrons does not move with constant velocity because they interact with crystall lattice. So they should emit energy in the form of EM waves. Does electrons emit EM waves during their movenment in conductors? What is the magnitude of the energy loss?

IMHO the magnitude of the loss of kinetic energy is huge, because acceleration is huge.

 

[Quandry]

Skin effect is explained by a very simple concept and by looking at the field distribution of a straight line conductor.
The field strength is strongest at the centre of the conductor. As the AC current varies the field collapses and regenerates in opposing directions according to the frequency. The varying field induces a reactive impedance (back emf) in the conductor which varies with field density. This impedance is strongest at the centre of the conductor and weaker at the surface. Since current follows the least impedance path, the current tends to flow in the conductor surface (the skin).
You will find that in high power high frequency transmitter sites the HF power conductors are hollow copper tubes. Not because they conduct better, but because to fill them is a waste of copper.

 

[Drakkith]

Does electrons emit EM waves during their movenment in conductors? What is the magnitude of the energy loss?

I'm sure they do, but remember that other than the surface electrons, the electrons are inside of the conductor, so any EM waves are quickly absorbed and turned into heat.

IMHO the magnitude of the loss of kinetic energy is huge, because acceleration is huge.

But what is the time frame for the acceleration? Is the electron being stopped almost completely, or is it mostly just scattering off a bit?

 

[Jackson Lee]

Skin effect is explained by a very simple concept and by looking at the field distribution of a straight line conductor.
The field strength is strongest at the centre of the conductor. As the AC current varies the field collapses and regenerates in opposing directions according to the frequency. The varying field induces a reactive impedance (back emf) in the conductor which varies with field density. This impedance is strongest at the centre of the conductor and weaker at the surface. Since current follows the least impedance path, the current tends to flow in the conductor surface (the skin).
You will find that in high power high frequency transmitter sites the HF power conductors are hollow copper tubes. Not because they conduct better, but because to fill them is a waste of copper.

Oh, your explanation is clear and helpful. I suppose I get it. Besides, could you please explain from Wiki perspective? I have attached it at the first page. Perhaps, you will feel it interesting as well. Thx a lot.

 

[sophiecentaur]

IMHO the magnitude of the loss of kinetic energy is huge, because acceleration is huge.

Do the Math. What is the Mass involved? (One electron per atom ) what is the drift velocity? (Say 1mm/second) How much KE would there be in 1g of wire?