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Homework Help: Magnetic force question - should be easy

  1. Nov 16, 2008 #1
    1. The problem statement, all variables and given/known data

    1) An electron moves in a magnetic field B = .50 i with a speed of 1.0 x 10^7 m/s 45 degrees above the positive y axis. What is the magnetic force on the electron?

    2. Relevant equations

    3. The attempt at a solution
    1)This should be an easy question, but I am getting my signs messed up.

    F=qvBsin(theta) q = 1.60*10^-6 v= 1.0 * 10^7 m/s B = .50 T
    F= (1.60*10^-6)(1.0*10^7)(.50) = 8.0 *10 ^ -13 +

    Now, using the right hand rule I believe that if this were a proton, the components would be
    (-5.66*10-13)i + (5.66*10-13)k and so then I just flipped the signs:

    (5.66*10-13)i - (5.66*10-13)k , but my book says they are both negative.

    Please help, I am confused by this. Is there a better way to think about this?
  2. jcsd
  3. Nov 16, 2008 #2
    any thoughts would be greatly appreciated
  4. Nov 17, 2008 #3
    I have also tried doing the cross product between v and B and then multiplying by 1.60 * 10 -19 but then I come up with a positive z component and a negative j component
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