How do they measure the mass of the electron in units of MeV/c*c ?

  1. What is the experimental system used to determine that an electron has a mass of 0.511 MeV/c*c ?

    I'd like to learn about methods other than Millikan's oil drop and Thomson's charge/mass ratios. What is the modern way to generate a value with those units?
    Last edited by a moderator: Aug 30, 2004
  2. jcsd
  3. arivero

    arivero 2,991
    Gold Member

    You can give some credit to nuclear beta decay.
  4. The units come from the equation E =mc^2

    If you re-rewite the equation in terms of units eV = kg c^2 and re-arrange it for mass, you get kg = eV/c^2

    and so the numerical value for the mass of the electron is equal to the numerical value of its energy/c^2. So we can give mass in terms of eV/c^2
  5. I understand what you are saying, but I believe that there is some sort of experimental equipment setup that can and has been used to physically measure the 0.511 MeV or 0.511 MeV/c2 values. It is that info I am after. I would be grateful for any references or links that reveal the nature of that experimental equipment.
  6. Nereid

    Nereid 4,014
    Staff Emeritus
    Science Advisor
    Gold Member

    Observations of the energy/wavelength/frequency of the gammas which result from the annihilation of electrons and positrons?
  7. Tom Mattson

    Tom Mattson 5,539
    Staff Emeritus
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    There is no experimental method to single out any system of units. It doesn't matter if you report the measured value of the mass in kilograms, slugs, or dynes/g. You can always convert to MeV/c2.
  8. Hello! I'm also confused regarding these units, given the equation E=[tex]\gamma[/tex]mc2, i am to show the mass of a proton in the units MeV/C^2, however i have no idea how to convert into these units. Is this form of the display of mass actually a measure of the relativistic energy that the particle has?
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