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Homework Help: Find Torque of a looped wire

  1. Jul 15, 2008 #1

    An eight turn coil encloses an elliptical area having a major axis of 40.0 cm and a minor axis of 30.0 cm. The coil lies in the plane of the screen and has a 5.85 A current flowing clockwise around it. If the coil is in a uniform magnetic field of 2.02 10-4 T directed toward the left of the screen, what is the magnitude of the torque on the coil? (Hint: The area of an ellipse is A = πab, where a and b are, respectively, the semimajor and semiminor axes of the ellipse.)


    I'm not sure what i'm doing wrong because this is plug in and calculate problem with the equation for torque. I'm guessing the angle would be 90 in this case so sin 90 = 1. The answer i came up with was .00356 N*M
  2. jcsd
  3. Jul 15, 2008 #2


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    Hi ketchuppy,

    Please post the details of what you did (as in, what numbers you used and what you did with them). My guess is that you read the hint incorrectly and used 40cm and 30cm for [itex]a[/itex] and [itex]b[/itex], but without your work I can't be certain.
  4. Jul 15, 2008 #3
    I used the equation Torque = NAIB Sin angle

    N= 8
    A= .376 m^2
    I = 5.85
    B= 2.02 10-4 T
    for the angle i used 90 degrees
  5. Jul 15, 2008 #4


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    I believe this area is incorrect, which is what I was referring to in my last post. The problems gives numerical values for the major axis and minor axis (40 cm and 30cm).

    But in the hint, the values of [itex]a[/itex] and [itex]b[/itex] to use in the area formula are the semimajor and semiminor axis.
  6. Jul 15, 2008 #5
    TY I didn't see that it was semi. =)
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