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Electromagnetism, finding magnetic field strength

  1. Jun 3, 2013 #1
    1. A 0.034 kg copper rod is hung by two wires and placed in a constant magnetic field. A current
    of 14 A runs through the 0.050 m long copper rod, making it hang at an angle of 34° from the vertical as attached in the diagram.

    What is the magnetic field strength holding the copper rod in this position?

    A. 27×10-1 T
    B. 32×10-1 T
    C. 39×10-1 T
    D. 48×10-1 T

    2. Relevant equations


    3. The attempt at a solution

    The thing is, I don't really know where to start.

    I know that the rod is at 34° (not perpendicular), so I know the formula [itex]\phi[/itex]=B×Acosa has to be involved somehow. However, I'd only be solving for [itex]\phi[/itex] and I don't know the area so that really isn't very helpful.

    I'm also given I and l to find B, and the only equation that looks has these variables is F=IlB. But that would me I need to find force and the other equation is F=QvB and we don't have many variables in that one.

    Attached Files:

  2. jcsd
  3. Jun 4, 2013 #2

    Simon Bridge

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    Start by drawing a free body diagram.
  4. Jun 4, 2013 #3
    Okay, I think I got it. So I would solve for the force of tension in the wires and that would be the F. Then I would do B=F/Il.

    Just one more question: when I finish solving for FT, would I have to double it to find F (since there are two wires)?
  5. Jun 4, 2013 #4

    Simon Bridge

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    It's basically a pendulum (use the side view).
    If the tension in each wire is T, then the total tension is 2T.
    Did you remember the magnetic force and gravity?
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