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Magnetism - Circular Loop in a Perpendicular Magnetic Field

  1. Apr 6, 2010 #1
    1. The problem statement, all variables and given/known data
    A circular loop carries a current I. It is placed in a constant magnetic field in such a way that the field lines are perpendicular to the plane of the circle. What is the force on the loop? Does the magnetic field have any effect on the loop described?

    2. Relevant equations
    F=qv x B
    F=IL x B

    3. The attempt at a solution
    I assume the answer should be something simple, like zero, since we are not given any information about the magnitude of B.
    I'm not sure how to apply a cross product formula, since I is not in a single direction but rather in a loop. If I think about applying the cross product (with the right hand rule) at every point along the loop, I am thinking that maybe all the forces cancel out so that there is no net force, but I am not sure.
  2. jcsd
  3. Apr 6, 2010 #2


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    Homework Helper

    Try that.
  4. Apr 6, 2010 #3
    "Any effect" is a pretty broad question.

    It is a fundamental idea that a closed loop of wire experiences no net force from a B-field...yes, you're right, they do cancel. Don't worry about the cross product formula just do some RH Rule observations for a few points on the circle using the direction of the current at that point for your velocity vector. You'll quickly realize how they cancel w/o any math needed ; )
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