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Homework Help: Electric field strenth question

  1. Feb 23, 2010 #1
    A Crossed-field velocity selector has a magnetic field of magnitude 1.0 x 10^-2T. What electirc field strenght is required if 10.0 keV electrtons are to pass through undeflected?

    ef - 1.0 x 10^-2

    I know it gives magnetic field, except how and what formula do we use to figure out the electric field strenght when we are also given 10.0 keV?
  2. jcsd
  3. Feb 23, 2010 #2


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    You should write down the relevant equations for the magnetic forces and the electric forces. You'll find that your answer of "ef - 1.0 x 10^-2" isn't quite right. Some of the relevant equations are a function of velocity.

    "10.0 keV" is a measure of energy; kinetic energy in this case, to be specific. Do you know of any unknown variables in your magnetic or electric field/force equations that you might be able to determine if you happened to know the kinetic energy of the electrons?
    Last edited: Feb 23, 2010
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