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How Relativity Connects Electric and Magnetic Fields

  1. Oct 13, 2006 #1

    I came to the following article, and I have a questions about it:


    From this article, it seems that if the electric current is not flowing in a wire, but instead in vacuum there will be no repelling force (since there is no background positive charge). If there is no repelling force, what we call magnetic field in the wire frame of reference will not exist.

    Can I conclude that an electric current does not create a magnetic field if it is flowing in vacuum?
  2. jcsd
  3. Oct 13, 2006 #2


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    Staff: Mentor

    When you remove the wire and its positive charges, in the second frame you do eliminate the electric field that the positive charges produce. However, in the first frame (the "wire frame") you now have to take into account the electric field that the negative charges produce!

    The electric field produced by the negative charges has a different magnitude in the two frames, because the charge density is different in the two frames.
  4. Oct 13, 2006 #3
    I think that the game with infinitely long wires is counterproductive. Have a look at JEMWA 20 No.9 1189 2006 "Relativistic derivations of electric and magnetic fields generated by an electric point charge moving with constant velocity"
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