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Homework Help: Electron Velocity Selector

  1. May 6, 2015 #1
    1. The problem statement, all variables and given/known data

    What is the velocity of a beam of electrons that go undeflected when passing through crossed electric and magnetic fields of magnitude 6.8 kV/m and 4.9 mT, respectively?

    What would be the radius of the electron's orbit if the electric field were turned off?
    2. Relevant equations

    v = E/B

    3. The attempt at a solution

    I got the first part by using the equation above. (I converted the measurements because I'm looking for m/s). So 6.8 kV/m is 6800 V/m and 4.9 mT is .0049T.

    v = E/B
    v = (6800V/m)/(.0049T)
    v = 1.3877*10^6 m/s

    For the second part, I am a bit confused as to how to find the radius (which equation to use?).
  2. jcsd
  3. May 6, 2015 #2


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    Homework Helper

    What force acts on a charged particle in magnetic field? That force provides the centripetal force for the circular motion.
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