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Homework Help: Need help with a physics problem!

  1. Dec 4, 2004 #1
    The problem says:

    A long piece of wire with a mass of .100 kg and a total length of 4.00m is used to make a square coil with a side of 0.100 m. The coil is hinged along a horizontal side, carries a 3.40-A current, and is placed in a vertical magnetic field with a magnitude of 0.0100 T. (a) Determine the angle that the plane of the coil makes with the vertical when the coil is in equilibrium. (b) Find the torque acting on the coil due to the magnetic force at equilibrium.

    I am having trouble solving for the angle that the coil makes with the vertical...

    Any help is greatly appreciated!
  2. jcsd
  3. Dec 4, 2004 #2
    Can someone please help me?

    I know that the equation T = BINAcos(theta) has to do with it and i can solve the torque to be .0034 Nm without the cos(theta) from the angle that the plane makes with the vertical but I have absolutely no idea how to solve for theta from the information that is given in the problem.

    I also tried to solve for theta using F = BILsin(theta) using the mass to calculate the force by setting it equal to the weight which is mg then plugging in B, I and L but when I tried to use arcsin to solve for theta the number that I got was out of the domain of sin.

    What I had was

    wt = mg
    wt = (.100kg)(9.81 m/s/s)
    wt = .981 N
    F = .981 N
    F = BILsin(theta)
    .981 N = (.0100T)(3.40A)(4.00m)sin(theta)
    then I got:
    sin(theta) = 7.213 and obviously this number is out of the domain of sin so I can't take the arcsin of it...

    can someone please tell me what I did wrong or point me in a more correct direction because i am 100% stumped..
    Last edited: Dec 4, 2004
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