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E field outside a current carrying wire

  1. May 5, 2012 #1
    1. The problem statement, all variables and given/known data

    One step in one of the problems in my book (involving calculation of the Poynting vector) asks to find the electric field outside a wire. This wire is resistanceless and the current is steady.

    2. Relevant equations

    Maxwell's.

    3. The attempt at a solution

    Stared at it for a while, had no idea how there would possibly be an electric field, solutions manual says the wire creates a radial one proportional to 1/r.
     
  2. jcsd
  3. May 5, 2012 #2
    Hmm. This is a strange question. It seems your book is claiming that there is some linear charge density produced by the current, which then that makes a 1/r radial field. However, the linear charge density assumes a static scenario, which you don't have. Really, the way a wire works is that there is some potential across it V=IR, and the field is the gradient of the voltage (or, alternatively, the field is J/resistivity where J is current density).
     
  4. May 5, 2012 #3
    Would this have anything to do with special relativity? I remember seeing something about length contraction when switching reference frames once, and about how that produced a charge density out of nowhere.

    Edit: what if there's a nonzero resistance?
     
  5. May 6, 2012 #4

    tiny-tim

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    which book? :confused:
     
  6. May 6, 2012 #5
    5th edition of HRK's Physics, chapter 38, problem 11.
     
  7. May 6, 2012 #6

    tiny-tim

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