Change of measurement units

1. Oct 27, 2005

asdf1

how do you change the measurement unit for an electron mass from kg to MeV/c^2?

2. Oct 27, 2005

andrevdh

use Einstein's famous equation
$$E=mc^2$$
and use the conversion for joules per electron volt.

3. Oct 27, 2005

asdf1

thanks!!! :)

4. Oct 28, 2005

andrevdh

It is a pleasure.

5. Oct 30, 2005

asdf1

@@a i'm still having trouble doing the calculations~
could you write out the whole equation to transfer the mass of an electron from kg to Mev?

6. Oct 30, 2005

big man

You know the mass of the electron and you know the speed of light. Just plug those into $$E=mc^2$$. You will have an energy value in terms of joules. Since you also know that one electronvolt is equivalent to $$1.602*10^-^1^9$$ joules, you can find the energy value in terms of electronvolts instead. Rearrange the original expression and you can reexpress the mass in terms of $$MeV/c^2$$.

Last edited: Oct 31, 2005
7. Oct 31, 2005

andrevdh

It is amazing how much confusion such a deceptively simple formula can generate. First calculate the rest mass of an electron:
$$\begin{split*} E_e = m_ec^2 \\ \ = 9.11 \times 10^{-31} \times (3.0 \times 10^8)^2 \\ \ = 8.2 \times 10^{-14} \ joule \\ \ = 512 \ keV \\ \ = 0.512 \ MeV \\ \ m_ec^2=0.512 \ MeV\end{split*}$$
Now get the mass in the "strange" new units:
$$m_e=0.512 \ MeV/{c^2}$$

Last edited: Nov 1, 2005
8. Oct 31, 2005

asdf1

thank you very much!!! :)