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Homework Help: Deriving torque from a B field on a magnetic Loop

  1. Sep 27, 2009 #1
    1. The problem statement, all variables and given/known data
    A wire ring lies in the xy-plane with its center at the origin. The ring carries a counter clockwise current I. A uniform magnetic fireld B is the the +x direction.
    There are a few parts to the question (Note: Everything except for I is a vector):
    1. show that dL = R*d(theta)*(-sin(theta)i + cos(theta)j) and from this Find dF = I*dL x B
    2. From part 1, find d(tau) = r x dF. Where r = R(cos(theta)i + sin(theta)j) is the vector from the center of the loop of the element to dl. (dl is perpendicular to r). Show that the result can be written as: tau = mu x B.

    2. Relevant equations
    dL = R*d(theta)*(-sin(theta)i + cos(theta)j)
    dF = I*dL x B
    d(tau) = r x dF
    r = R(cos(theta)i + sin(theta)j)
    tau = mu x B
    i is the x-direction
    and j is in the y.

    3. The attempt at a solution
    Probably not worth writing
  2. jcsd
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