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Homework Help: Magnetic force on one electron

  1. Apr 5, 2012 #1
    1. The problem statement, all variables and given/known data
    question - see image
    attachment.php?attachmentid=45908&d=1333628221.png


    2. Relevant equations



    3. The attempt at a solution

    so I use the equation F = BIl
    F = 0.2 * 0.4 * 8 = 0.64
    Surely I just divide it by the number of electrons (8*1028) to get the answer
    BUT this does not give the correct answer.

    The correct answer is D???
     

    Attached Files:

  2. jcsd
  3. Apr 5, 2012 #2

    gneill

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    Staff: Mentor

    Ah. That's not the number of free electrons, that's the density of free electrons.
     
  4. Apr 5, 2012 #3
    so density / area = number/m
    right?
     
    Last edited: Apr 5, 2012
  5. Apr 5, 2012 #4

    gneill

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    Staff: Mentor

    ##\rho = \frac{n}{volume}##

    If you calculate the volume of the wire you can find the total n.
     
  6. Apr 5, 2012 #5
    so n = density * volume
    n = 8 * 1028 * 0.4 * 10-6

    therefore answer = D

    thanks
     
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