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Homework Help: Ampere's Law for current carrying wire

  1. Apr 12, 2012 #1
    1. The problem statement, all variables and given/known data

    Use Ampere's Law to show that the equation for the magnetic field inside a current carrying wire is (1/2)μJr where J is the current density (assumed constant).

    2. Relevant equations


    3. The attempt at a solution


    B*ds=B(ds)cosθ I think θ is 0 in this situation?

    ∫Bds=μI I believe r is length. If so would I=Jr?


    From here I don't know what to do. What would my limits of integration be?
  2. jcsd
  3. Apr 12, 2012 #2


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    hi btpolk! :smile:
    no, r is radius

    and J is the current per cross-section area
  4. Apr 12, 2012 #3
    That said, i'm guessing I would treat the wire as a cylinder and the limits of integration would be 0 to 2pi? Also where does the J come in? Would it be some kind of substitution for I?
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