I read link given below:


Above link says

_The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic wave, not the movement of electrons. Electromagnetic wave propagation is fast and depends on the dielectric constant of the material. In a vacuum the wave travels at the speed of light and almost that fast in air.


Since the velocity of propagation is very high — about 300,000 kilometers per second — the wave of an alternating or oscillating current, even of high frequency, is of considerable length. At 60 cycles per second, the wavelength is 5,000 kilometers, and even at 100,000 hertz, the wavelength is 3 kilometers. This is a very large distance compared to those typically used in field measurement and application._

It gives wavelength of EM wave in wire. How did they find it?

Edit : After reading comments

Also, why do you all say, it has nothing like that. That there is no such wavelength. Is Wikipedia wrong here then?

Edit 2 : I got that what wiki said was something different. They simply used $v = \lambda \nu$

Now, I wonder that electric field is caused by virtual photons. What is their frequency and wavelength in wire?


closed as unclear what you're asking by John Rennie, user36790, John Duffield, Kyle Kanos, Gert Nov 26 '15 at 20:15

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  • $\begingroup$ The carriers are rather slow: en.wikipedia.org/wiki/Drift_velocity $\endgroup$ – Timeless Nov 26 '15 at 15:54
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    $\begingroup$ Current has no velocity like this, it's only the number of carriers per unit time (I=dQ/dt). $\endgroup$ – Timeless Nov 26 '15 at 17:05
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    $\begingroup$ Yes, if the cables were empty and you would have to fill them up with electrons. But they are already full of electrons, and applying an electric field, all free electrons start to move. It's like the water tap at home, you don't have to wait for the water to come all way from a water reservoir, it's already in the water pipe. $\endgroup$ – Timeless Nov 26 '15 at 17:21
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    $\begingroup$ Re your last edit, when you connect the battery a signal that is basically a step function propagates along the wire at around $0.1c$ to $c$ depending on the type of wire. A step signal isn't a plane wave and doesn't have a frequency or wavelength. $\endgroup$ – John Rennie Nov 27 '15 at 10:23
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    $\begingroup$ You have to read the Wikipedia quote more carefully. It's saying they assign wavelength to the sinusoidal AC current of 60 Hz, not to any "electromagnetic wave". This wavelength is not the wavelength of any actual oscillation. $\endgroup$ – ACuriousMind Apr 22 '16 at 11:58

When you first connect the source, there is a very brief transient during which the steady-state DC solution is set up. The speed of the signal, i.e. the electromagnetic wave front that carries the information along the wire, is a bit less than the speed of light because of transmission line effects. Figuring out exactly how long the transient lasts would require a simulation that accounts for the distributed capacitance, distributed inductance, resistivity, and shape of the wire, not to mention the properties of the battery itself, but you can still make a rough estimate of the time constant as being the size of the system divided by the speed of light. For a small thing sitting on a table we're talking a nanosecond or so, so the transient will have a spread of frequencies roughly in the GHz range. It won't have a single well-defined frequency in general.

Once the transient is finished, you're now in a DC steady-state condition, and the frequency is 0 while the wavelength is infinite.


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