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

1. Aug 30, 2004

### what_are_electrons

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. Aug 30, 2004

### arivero

You can give some credit to nuclear beta decay.

3. Aug 30, 2004

### colinr

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

4. Aug 30, 2004

### what_are_electrons

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.
Thanks!

5. Aug 30, 2004

### Nereid

Staff Emeritus
Observations of the energy/wavelength/frequency of the gammas which result from the annihilation of electrons and positrons?

6. Aug 30, 2004

### Tom Mattson

Staff Emeritus
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.

7. May 11, 2011

### PatrickRowe

Hello! I'm also confused regarding these units, given the equation E=$$\gamma$$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?