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Confused about j hat in this magnetic field problem.

  1. Oct 2, 2011 #1
    1. The problem statement, all variables and given/known data
    A point particle has a charge equal to –3.64 nC and a velocity equal to
    2.75 10^3 m/s i. Find the force on the charge if the magnetic field is
    (d) 0.75 Ti + .75Tk

    The solution manual had a positive number. I thought it was a typo until I saw the next problem where they got the opposite sign of what I got again for j hat.
    F=qv x B, how is it possible that they got a + #?
  2. jcsd
  3. Oct 2, 2011 #2


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    I think that i x k = -j, just as you do. However, another negative sign enters into the equation by means of q, which is intrinsically negative here. Negative charges will move in the opposite direction of positive charges.
  4. Oct 2, 2011 #3
    OMG I'm so stupid I completely forgot about that, been too long since I did cross products. thanks a lot
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