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Magnetic Force on an Electron

  1. Jul 25, 2007 #1
    1. The problem statement, all variables and given/known data
    An electron in a vacuum is first accelerated by a voltage of 48200 V and then enters a region in which there is a uniform magnetic field of 0.183 T at right angles to the direction of the electron's motion. What is the force on the electron due to the magnetic field?

    2. Relevant equations

    F = qvBsintheta

    3. The attempt at a solution

    U = Vq (potential energy)
    1/2 mv^2 (kinetic energy)
    I set potential energy equal to kinetic energy to solve for velocity.

    Vq = 1/2 mv^2 (then solve for v)
    v = SQRT(2qv/m)

    F = qB(SQRT(2qv/m))sintheta
    Plugging in the numbers, I get
    F = (1.6e-19) (0.183T) (SQRT(2(1.6e-19)*48200V/9.11e-31))* sin (90)
    F = 3.82 e -12

    Is this the right way to do this problem? Thanks in advance for looking it over for me.
  2. jcsd
  3. Jul 25, 2007 #2


    User Avatar
    Homework Helper
    Gold Member

    You seem to be correct as long as the electron starts off at a velocity of 0, which I'm assuming it does since the problem does not state otherwise. I also get the same answer that you do. Nice job!
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