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EMwave in space and copper wire.

  1. May 25, 2009 #1
    We have a formulae to find energy contained by an EM wave, which finds energy per unit volume. Also says it is equally distributed between E and B fields.

    How do we find EM energy for an EM wave of 50Hz in a copper wire? Because it is low frequency, instead of space we guide by conducting copper wire.
    I want to know how it relates to energy formulae for EM wave in space.

    I know we can find it by Vrms and Irms but that is more on application side, easy way.

    Thanks in advance.
  2. jcsd
  3. May 25, 2009 #2


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    The energy density is also dependent upon the permittivity and permeability of the material. In free-space, this works together such that the contribution from the electric and magnetic fields are the same. But once you go to a dielectric or conductive material, the energy density can shift from one to the other. In the end though, you'll do the same thing as before, you'll have to solve for the fields in your transmission line system and do the appropriate spatial integrals to find the energy densities.

    The fields for a copper wire may be difficult to solve in closed-form but you should have good success with other forms of transmission lines, like a coaxial cable, which restrict the fields to a finite cross-sectional area of space. The only thing with a coaxial (as with most transmission line solutions) is that the solution will be in terms of modes. With a low frequency like 50 Hz, you will be exciting a large number of modes and thus you will need to calculate and determne the modes that will contribute most to your answer.
  4. May 26, 2009 #3
    Thanks, Now I know which book to refer :-)
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