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Homework Help: Magnitude of Torque on a current loop

  1. Apr 2, 2012 #1
    1. The problem statement, all variables and given/known data

    A small current loop of area A=0.0008m2 and moment of inertia I=6.9e-07kgm2 carries a current i=0.0039A with its magnetic moment perpendicular to the Earth's magnetic field. The magnitude of the Earth's field is B=4.2e-05T.

    a). What is the magnitude of the net torque T on the loop?
    T = ____ Nm

    b). What is the angular acceleration a of the loop?
    a = ___ rad/s2

    2. Relevant equations

    τ = NiABsinθ
    α = τ/I

    3. The attempt at a solution

    I have the equation for toque and I am given all of the variables. I assumed that N = 1, and θ = 90°. When I plug in all of the numbers, I get the following:
    τ = (1)*(.0039 A)*(.0008 m^2)*(4.2e-05 T)*sin90° = 1.3104*10-10 Nm. That is not the correct answer, however. I do not know what to do at this point. If I could get the torque, I would then be able to easily get the angular acceleration. Any help would be greatly appreciated. Thank you!!!
    Last edited: Apr 2, 2012
  2. jcsd
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