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Find the magnetic force on the square loop

  1. Jul 28, 2015 #1

    Abs

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    1. The problem statement, all variables and given/known data
    A square loop PQRS carrying a current of 6A is placed near a long wire carrying 10A as shown in the figure. Find the magnetic force on the square loop.

    2. Relevant equations
    F = B * i * l ....................... (1)
    B = (µ0 * i)/2 π r

    3. The attempt at a solution
    I tried finding out the answer by applying the formulas given above, I tried finding B [by (2) ]and putting it in the equation (1) but I did not get the correct answer.
    BTW the answer is
    1.6 x 10^-5 towards right. sum.png
     
  2. jcsd
  3. Jul 28, 2015 #2

    Hesch

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    You must find the B-field at the wires PQ, QR, RS and SP. Then find and add the forces.

    Hint: Consider the forces FPQ and FRS
     
  4. Jul 28, 2015 #3

    SammyS

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    Hello Abs. Welcome to PF !

    What did you get for the answer, and what are the details of how you got it?
     
  5. Jul 28, 2015 #4

    Abs

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    I got 1.22 x 10^4

    I first found out the magnetic force on P then S then Q and then R and took a mid point in the center of the square and I got four values and I found their arithematic mean and I got 1.22 x 10^4
     
  6. Jul 28, 2015 #5

    Abs

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    But we are supposed to find the force, then what good would it be to find force excewpt that it can be put in eqn (1)
     
  7. Jul 28, 2015 #6

    Hesch

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    Using F = B*I*L will not give any force at a mid point, which has a length = 0.
    Force = B-field * current * Length of wire.

    So find the B-field along the length SP, and find by use of (1) the force FSP, and so on.
     
  8. Jul 28, 2015 #7

    Abs

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    Wow, I made a big blunder there is nothing in the middle to be magnetized damn that was stupid of me.
    Thanks Hesch
    Just one more question,

    When I find B by B = (µ0 * i)/2 π r

    Do I have to find it for SR and PQ ? If yes then how do you find it in a horizontal wire ? I know how to find it in a vertical wire

    AND

    After I find all the Force(s) do I add them ?
     
  9. Jul 28, 2015 #8

    Hesch

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    As for RS and PQ the B-field will not be homogeneous, but anyway the forces FRS and FPQ will be symmetrical and counter-acting. So forget them.
    Yes. Be careful with directions.
     
  10. Jul 28, 2015 #9

    Abs

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    Biiiiiiig thanks Hesch I don't get it why are you so smart man I am jealous. Thanks.
    I will tell you positively by tomorow if I get the answer(it is my time to sleep now then school tutions ..... etc)
    Bye
     
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