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Net force on rectangular circuit

  1. Sep 6, 2015 #1
    1. The problem statement, all variables and given/known data
    upload_2015-9-6_3-20-28.png

    2. Relevant equations
    Right hand rules

    3. The attempt at a solution
    Am i correct for a? I drew my interpretations of the magnetic field around each section.
    For b) am i correct to think the internal net force in the rectangular wire is 0, and the only force acting on it is that of the long wire at the bottom. And if that is correct, which way is the net force acting on the rectangular loop?
     
  2. jcsd
  3. Sep 6, 2015 #2

    Titan97

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    For part a, all your forces have to be in opposite direction.
    F=i (L×B)
    For the bottom part, L is along ##-\hat i## and B is along ##\hat k##.
    L×B is along ##-\hat j## or downwards.
     
    Last edited: Sep 6, 2015
  4. Sep 6, 2015 #3
    Why are they in opposite directions? Does that not fit the right hand rule?
     
  5. Sep 6, 2015 #4

    rude man

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    yes
    where is the B field stronger, nearer the long wire or farther away from it?
     
  6. Sep 6, 2015 #5
    Near the long wire, then it must be acting downwards correct?
     
  7. Sep 6, 2015 #6

    rude man

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    Since you previously showed that you could determine the direction I'm giving you a "Yes".
     
  8. Sep 6, 2015 #7
    Ok, are the directions of the magnetic field around the rectangle wrong?
     
  9. Sep 6, 2015 #8

    rude man

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    They're wrong.
    Set up a coordinate system x to the right, y up, z out of page. Then evaluate the various unit vectors.
    E.g. for the top left segment we get i x -k = ?
    Learn the circular +/- i +/- j+/- k ↔ +/- i diagram for the signs. I find it a whole lot easier than twisting my hand and fingers into unnatural shapes ....
     
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