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Homework Help: Magnetic Field - Torque on a Current Loop

  1. Apr 1, 2009 #1
    1. The problem statement, all variables and given/known data

    A circular coil of 720 turns and area 0.6 m^2 is in a uniform magnetic field of 0.63 T. The maximum torque exerted on the coil by the field is 0.0026 N · m.

    a) Calculate the current in the coil.

    b) Assume the 720 turns of wire are used to form a single-turn coil with the same shape but much larger area. What is the current if the maximum torque exerted on the coil by the field is 0.0026 N · m?

    NOTE: Sigfigs do not matter

    2. Relevant equations

    T = IABn

    3. The attempt at a solution

    Part A:
    I solved by substitution using the equation T = IABn, getting T = 9.5532e-6 N · m (answer is correct)

    Part B:
    This is the part I'm having trouble with. I thought I could fine the new Area doing the following (I'm sure this approach is wrong):

    .6 = pi*r^2, r*720 = 314.7
    A = pi*314.7^2, plugging in the new area into T = IAB gives the wrong answer.

    I'd be very grateful for any help.
  2. jcsd
  3. Apr 1, 2009 #2


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    Homework Helper

    I got 1.32644e-8 N-m
  4. Apr 2, 2009 #3
    yeah, Thanks. I got the same answer or thereabouts.

    After some algebra (and some help) I found that the new area A2 = (n^2)*A1.

    Plugging that into T = IAB gives the correct answer.
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