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Homework Help: Force between Electric currents

  1. Oct 26, 2014 #1
    1. The problem statement, all variables and given/known data

    In a typical experiment to study the force between electric currents, identical fixed and movable wires were separated using a spacer thickness 0.6065cm. The radius of each wire was determined to be 0.162cm and the length of the movable wire was 26.5cm. The apparatus was set up so as to produce a repulsive force when a current of 9.3 A passed through the wires in opposite directions. Assume the magnetic permeability of free space, µ0 = 4p x 10-7 T.m/A.

    (a) Calculate the magnetic field strength at the center of the movable wire due to the given current through the fixed wire.

    (b) What mass(in milligrams) would have to be added to the weight pan on the movable wire to balance out the repulsive magnetic force when the given current passes through the fixed wire?

    (c) Calculate the magnitude of the total magnetic field due to the given current in the wires, along the perpendicular line between the wires at a point y=0.404cm, measured from the surface of the fixed wire when:

    (i) the current flows in the opposite direction in the two wires, and

    (ii) the current flows in same direction

    2. Relevant equations
    B = µ0 * I / 2pi*r
    F= ILBsintheta
    F/L = µ0 I1 I2 / 2pi * d

    3. The attempt at a solution

    (a) B = µ0 * 9.3A / 2pi * (0.162cm + 0.162cm + 0.6065cm) -> convert to meter
    B = 2 x 10^-4 Tesla

    (b) F = ILB sin theta (in this case L x B is perpendicular so it's 90 degree) and F = mg so
    mg = ILB
    m = ILB / g
    m = 9.3A * 0.265m * 2 x 10^-4 T / 9.81
    m = 5.02 x 10^-5 kg - > 50.2 mg

    (c) I am not quite sure on how to approach this problem, can someone give me a pointer and check to see if i did a & b correctly?

  2. jcsd
  3. Oct 27, 2014 #2
    Any ideas or suggestion?
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