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Magnetic field far from the origin

  1. Jul 1, 2015 #1
    1. The problem statement, all variables and given/known data
    An important result in the theory of antennas, is that if a current passes through the ZZ axis, the magnetic field far from the origin can be expressed in spherical coordinates, using only one componente of the magnetic vector potential.
    Prove that:
    Code_Cogs_Eqn_2.gif

    2. Relevant equations
    The magnectic field for a straight wire is mu0*I/(2*pi*r), and B=∇xA.

    3. The attempt at a solution
    This was in my exam last week, and i have no idea how to solve it... I've tried stating with the magnetic field of a straight wire, but i don't know how to relate that with the curl of A. Can you guys please help me out?
     
  2. jcsd
  3. Jul 6, 2015 #2

    tech99

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    Gold Member

    Well I think at a great distance, we are talking about the magnetic field of the radiated EM wave. These fields, when radiated from a short conductor, will fall off inversely with distance, have a maximum at 90 degrees to the conductor and a radiation pattern which falls off with the cosine of this angle. Maybe this description will help?
     
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