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Torque on current loop

  1. Oct 16, 2009 #1
    1. The problem statement, all variables and given/known data
    A wood cylinder of mass m = 0.250 kg and length L = 0.100 m with N =10 turns of wire wrapped around it longitudinally, so that the plane of the wire coil contains the long axis of the cylinder. The cylinder is released on a plane inclined at an angle theta to the horizontal, with the plane of the coil parallel to the incline plane. If there is a vertical uniform magnetic field of magnitude 0.5T, what is the least current i through the coil that keeps the cylinder from rolling down the plane?


    2. Relevant equations
    force = NiL x B


    3. The attempt at a solution
    The answer is 2.45A, i try to find all the forces and solve when torque is zero, but i cant elimate the sin theta or cos theta thing. Please help, thankyou.
     
    Last edited: Oct 16, 2009
  2. jcsd
  3. Oct 16, 2009 #2

    Redbelly98

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    Can you show what you worked out so far? It might be possible for somebody to spot your error (if any) that way.

    p.s. if it helps, you can copy-and-paste this theta symbol: θ
     
  4. Oct 16, 2009 #3
    2NiLBr sinθ = μmgr cosθ
    mgsinθ = μmg cosθ

    the answer is 2.45 if g = 9.8, i used 10 before lol, correct now?
     
    Last edited: Oct 16, 2009
  5. Oct 17, 2009 #4

    Redbelly98

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    Looks good (I presume you are able to eliminate the sinθ & cosθ now). :smile:
     
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