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Homework Help: Copper wire magnetic field

  1. Sep 10, 2007 #1
    A piece of copper wire has a resistance per unit length of 6.40e-3 ohm/m. The wire is wound into a thin, flat coil of many turns that has a radius of 0.190 m. The ends of the wire are connected to a 12.0 V battery. Find the magnetic field strength at the center of the coil.

    R/L = 6.40e-3 ohm/m
    r = 0.190 m
    V = 12.0 V
    u0 = 4pi e -7 Tm/A
    B = ? T

    V = IR (I = V/R)
    B = u0 * n * I
    so B = u0 * n * (V/R)

    I don't know where to go from here.
  2. jcsd
  3. Sep 10, 2007 #2


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    Start by finding L in terms of n. That may be your missing ingredient.
  4. Sep 10, 2007 #3
    n = turns/L
    L = R/6.40e-3 ?
    im lost here
  5. Sep 10, 2007 #4


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    Did you post the question exactly?

    What I'm thinking is... can't you arbitrarily make the coil longer, keeping the number of turns/unit length the same... but increasing the resistance... thereby lowering the current. And that would lower the magnetic field?

    So is there a unique solution to this problem?
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