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Homework Help: Potential Energy and Torque in a Magnetic Field

  1. May 25, 2010 #1
    1. The problem statement, all variables and given/known data

    The coil in the figure below carries a current of 2.00 A in the direction indicated, is parallel to an xz plane, has 3 turns, an area of 4.20 10-3 m2, and lies within a uniform magnetic field = (2.20 - 2.85 - 3.65 ) mT.

    (a) What is the magnetic potential energy of the coil - magnetic field system?

    (b) What is the magnetic torque on the coil?

    2. Relevant equations

    U = -u (dot product) B

    T= -u (cross product) B

    3. The attempt at a solution

    So, in order to calculate the Potential Energy, I tried to take the magnitude of B and multiply it by the dipole moment. I got 1.29e-4. For some reason, this is not correct. I know I should not include one of the vectors of B. I tried not including the x and z vectors, but that didn't work. I also tried to not include the y vector, but that didn't work either. I have no idea what to do!
    For the second part, I know how to take the cross product, but I do not know what the vector form of u is. I know the y vector is 0, but how do I find the x and z vector? i tried simply using <u,0,u>, but that didn't work.
    Thank you for your time!
  2. jcsd
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