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Homework Help: Magnetic Field in a Cylindrical Conductor

  1. Nov 24, 2011 #1
    1. The problem statement, all variables and given/known data

    A cylindrical conductor of radius R = 2.49 cm carries a current of I = 2.17 A along its length; this current is uniformly distributed throughout the cross-section of the conductor. Calculate the magnetic field midway along the radius of the wire (that is, at r = R/2).

    Radius (m) = 2.49 cm = 0.0249 m = 0.01245 m (as asked)
    Current (I) = 2.17 A

    2. Relevant equations

    I thought it was B = µI / 2πr because i was given a sheet of equations and this was the only one that seemed to fit it.

    3. The attempt at a solution

    B = µI / 2πr
    B = (4π x 10^-7)(2.17) / 2π(0.01245)
    B = 3.49e-5 T

    Though this isn't the right answer. Not sure what's gone wrong here.
    I also thought it was zero since it's a "conductor" also not right...
  2. jcsd
  3. Nov 24, 2011 #2
    Not to worry, i got the answer. I was using the wrong equation.
    For values of Magnetic Field inside the given radius the equation is

    B = µIr / 2πa^2
    B = (4π x 10^-7)(2.17)(0.01245) / 2π(0.0249^2)
    B = 8.71e-6 T

    In case anyone else had the same or similar problems.
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