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Magnitude of force on electron in magnetic field

  1. Oct 13, 2013 #1
    1. The problem statement, all variables and given/known data
    An electron in a vacuum is first accelerated by a voltage of 41300 V and then enters a region in which there is a uniform magnetic field of .145 T at right angles to the direction of the electron's motion.

    What is the magnitude of the force on the electron due to the magnetic field?
    2. Relevant equations
    [itex]F=qvBsinθ[/itex]
    3. The attempt at a solution
    At first I though the 41300 V was just a number to throw me off (they do that a lot), but now I think it is important. I know the charge, magnetic field, and sin90=1. So the only thing I'm missing is velocity, but I have no clue how to calculate that from the information I was given. Any help?

    Thanks
     
  2. jcsd
  3. Oct 13, 2013 #2
    You can find the energy of an electron by using qV = U, where U is the Kinetic Energy of the particle. Then it's just a matter of solving for v from the KE equation.

    EDIT: I should point out that the energy will be in eV, which you can then just use a conversion factor to get it into joules.
     
  4. Oct 14, 2013 #3

    rude man

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    The electron is moving fast enough to warrant relativistic correction for calculating the velocity.
     
  5. Oct 14, 2013 #4
    Perfect. Thanks
     
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