Some confusion on electron volt

1. Aug 30, 2009

dragonlorder

1. The problem statement, all variables and given/known data
I learned that by definition, one electron volt is the kinetic energy an electron would have moving between 1 voltage difference. if an electron moves between voltage of 1 million volts,then K = 1MeV, for example, but the problem is K is expressed in 1/2mv^2 or the relativistic one (gamma-1)mc^2

2. Relevant equations

3. The attempt at a solution

2. Aug 30, 2009

rl.bhat

In an electric field E the electron experiences a force F = e*E
Due to this force the electron moves a distance x, and the work done W = e*x*E.
This work produces kinetic energy in electron = 1/2*m*v^2
If the electric field is uniform Voltage = x*E

3. Aug 30, 2009

dragonlorder

oh, so its defined in classical sense. I thought that since relativistic one was correct, so it might be the relativistic energy, but no. Thanks ~

4. Aug 31, 2009

Redbelly98

Staff Emeritus
No, for relativistic energies the relativistic formulas must be used.

1/2 m v^2 only works in non-relativistic situations.

5. Aug 31, 2009

dragonlorder

yea, later I found out any electron moving through 1V, must carry 1eV energy by definition, doesnt depend on which formula I use. In high speed, relativistic, of course