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Homework Help: Some confusion on electron volt

  1. Aug 30, 2009 #1
    1. The problem statement, all variables and given/known data
    I learned that by definition, one electron volt is the kinetic energy an electron would have moving between 1 voltage difference. if an electron moves between voltage of 1 million volts,then K = 1MeV, for example, but the problem is K is expressed in 1/2mv^2 or the relativistic one (gamma-1)mc^2

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Aug 30, 2009 #2


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    In an electric field E the electron experiences a force F = e*E
    Due to this force the electron moves a distance x, and the work done W = e*x*E.
    This work produces kinetic energy in electron = 1/2*m*v^2
    If the electric field is uniform Voltage = x*E
  4. Aug 30, 2009 #3
    oh, so its defined in classical sense. I thought that since relativistic one was correct, so it might be the relativistic energy, but no. Thanks ~
  5. Aug 31, 2009 #4


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    No, for relativistic energies the relativistic formulas must be used.

    1/2 m v^2 only works in non-relativistic situations.
  6. Aug 31, 2009 #5
    yea, later I found out any electron moving through 1V, must carry 1eV energy by definition, doesnt depend on which formula I use. In high speed, relativistic, of course
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