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Homework Help: Magnetic Fields and total force

  1. Nov 29, 2006 #1

    Given that B = (6x, -9y, 3z) find the total force experienced by a rectangular loop in the z = 0 plane:

    Loop defined as...

    with 5 Amp current flowing COUNTERclockwise.
  2. jcsd
  3. Nov 29, 2006 #2
    1) according to our guidelines, you need to show us what you have done
    2) what is the formula that you would use here ?
    3) are you sure you have all the data that you need ?

  4. Nov 29, 2006 #3
    1) I guess I got a little anxious with the submit button!

    I'm having problems setting up the equation.

    2) I believe we're to use the equation: F = Int(dl x B) (where "x" indicated a cross product.)

    I know I need to apply superposition to the loop - doing the integral for each of the four sides of the loop.

    My problem comes from finding dl. Maybe I'm approaching the problem from the wrong angle. I initially thought you would use the integral relating B and the length of the loop in differential form.

    3) I've submitted all information given, but I'm unclear if there's an intermediate step to solve extra needed data.
    Last edited: Nov 29, 2006
  5. Nov 29, 2006 #4


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    Sinde the field is constant, your integral reduces to a sum of four terms for the four sides of the loop, where each term is of the form (Bold is vector)

    F = I L x B
  6. Nov 29, 2006 #5
    With that analysis I keep getting the total resultant force as zero. Does this make any sense?
  7. Nov 29, 2006 #6


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    What happens to the force when you reverse the current in a wire? You have pairs of opposite currents, so it absolutely does make sense. Torque would be a different matter.
  8. Nov 29, 2006 #7
    That's right! Thank you so much for the help!
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