# How to express the mass of a proton and an elektron in MeV/c²? Thank you!

## I know how to express something in MeV/u and I know how much c² is... But i can't make up my mind how to do this?

As you know mass and energy are inter-convertible ($E = m {c}^{2}$) and an energy can also be expressed as a charge multiplied by a p.d. (voltage) as $E = Q . V$
This means that physicists often express the masses or energies of subatomic particles in eV, but of course if we rearrange the first equation for mass we get $m = \frac{E}{c} ^ 2$ so formally all energies quoted in eV (or MeV, GeV etc.) should actually be quoted as $\frac{e V}{c} ^ 2$ but laziness prevents it and it is just quoted as eV.