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Homework Help: Magnetic/Electric Field

  1. Oct 16, 2008 #1
    A beam of electrons is accelerated through a potential difference of 11kV before entering a velocity selector. If the B-field of the velocity selector is perpendicular to the velocity and has a value of 0.05 T, what value of the E-field is required (in the magnetic field region) if the particles are to be undeflected?

    What I know:
    F = qvB
    and
    F = qE

    Therefore E = vB

    But how on earth do I find the velocity? Please help!
     
  2. jcsd
  3. Oct 16, 2008 #2
    Read this again:
    "A beam of electrons is accelerated through a potential difference of 11kV"
    What energy will the electrons have?
     
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