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How The Mass Of an Electron Was Worked Out

  1. Oct 1, 2007 #1
    I was just wondering how the rest mass of an electron was first discovered, I've searched everywhere and think you guys are probably the ones that are most likely going to be able answer this question.
  2. jcsd
  3. Oct 1, 2007 #2


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  4. Oct 1, 2007 #3


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    The Millikan experiment was originally intended to show charge quantization. I wonder how one could determine the electron mass from this experiment at all because one oil drop has a mass that's by orders of magnitude larger than the electron's mass.

    But if one has shown that charge is quantized one only has to shoot an electron beam of specific velocity into a magnetic field and then determine the radius of the circular orbit it takes (for filtering a certain velocity one uses crossed E and B-fields => I think this is called Wien filter) You get the charge to mass ratio e/m and from this you can easily calculate m.

    Wikipedia seems to say that it was J.J. Thompson himself who measured the charge to mass ratio in 1897. According to one of my books a man named Kaufmann discovered the velocity dependence of electron mass in 1901 (four years before the formulation of special relativity).
    Last edited: Oct 1, 2007
  5. Oct 1, 2007 #4
    In summary, J.J. Thompson performed the experiment which measured the charge-to-mass ratio of the electron. Millikan later performed the experiment which measured the electron charge, also determining the electron mass.
  6. Oct 3, 2007 #5
    Thanks for your quick responses everyone
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