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Homework Help: Find the current in the coil

  1. Jul 7, 2006 #1
    "The magnetic field at the center of a 50-turn coil of radius 15 cm is 0.60mT. find the current in the coil."
    N=50, r = .15m, B = 6.0 * 10^-4 T, magnetic permeability = 4 * pi * 10^-7.

    B = (mag.per. * N * I)/ L
    However, I don't have L, which is the length. I do have r, the radius, but it's not in the equation... How do i solve this?
  2. jcsd
  3. Jul 7, 2006 #2
    This is not a solenoid, just a ring of wire. A hoola hoop.
  4. Jul 7, 2006 #3
    then what does "a 50-turn coil" mean?
    my book gives me the equation for finding the magnetic field in the center of a circular loop: B = (mag. per. * I)/(2r). But then how do I factor the "50-turn coil" in? Is this simply superfluous information?
  5. Jul 7, 2006 #4

    Doc Al

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    Staff: Mentor

    Think about it: You have the formula for the field at the center of a single circular loop of current-carrying wire, so what would you expect the field to be for 50 of them combined?
  6. Jul 7, 2006 #5
    50 times the strength I suppose...

    well, that does work out:
    1/50 B = (mag.per. * I)/(2r)
    and solving for I, I get: I = 2.9A, which is the right answer.

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