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Torque, Force, magnetic moment (please help)

  1. Apr 27, 2005 #1
    I'm not sure I know how to start this problem.

    "A rectangular coil has 16 turns and sides of lenght a=20 cm and c=50 cm. The coil is pivoted around the y-axis and its plane is at 30 degrees to a magnetic field B=50 k T. The current is 10 A
    a)Find the force on each side
    b)what is the magnetic moment of the coil?
    c)What is the torque on the coil? "

    How do I start this problem? I really have no idea
     
  2. jcsd
  3. Apr 27, 2005 #2

    OlderDan

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    You start by learning how to find the force on a current carying wire in a magnetic field. Find that and post it and we can take it from there.
     
  4. Apr 27, 2005 #3
    I know that F=IL x B = ILB sin 30 where I=10 L=20 and B = 50

    Am I on the right track?
     
  5. Apr 27, 2005 #4

    OlderDan

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    Yes. That is a good start. Now think about how many turns of wire are carrying that current, and the fact that there are four different straight-line segments of the loop.
     
  6. Apr 27, 2005 #5
    So, I'd have to find the force on each side individually.
    For the first side:
    F1 = 10A (0.2 m) i X 50 k ?

    Am I supposed to find the values of B (in the i and j direction)?
     
  7. Apr 27, 2005 #6
    So, to find the torque, I do:

    Torque = N(IAB sin 90)

    Once I have that, I can find the magnetic dipole moment using:
    Torque= u x B ?
     
  8. Apr 27, 2005 #7

    OlderDan

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    I assume you have a diagram to go with this problem, so you know which side of the coil is which, and I assume from your reply here that the two 20cm sides make the angle of 30 degrees with B. The 50cm sides make a different angle with B. You are on the right track with the first force, but there are 4 of them, and don't forget about the 16 turns. What does that do?
     
  9. Apr 27, 2005 #8

    OlderDan

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    There is a reason why part b) was asked before part a) The magnetic moment (magnetic dipole moment) of the loop is a property of the geometry of the loop and the current it carries. The torque depends on that magnetic moment, so the moment is in fact included in the equation for the torque. You would have to know how torque depends on the moment to do things in the order of c) then b), which of course can be done if you understand where the torque equation comes from. I suggest you do b) then c) and find out how to calculate the moment directly from the porperties of the coil.
     
  10. Apr 27, 2005 #9
    Thank for your help. I think I have figured it out
     
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