# Wavelength of 1.5keV (kinetic energy) electron

1. Aug 26, 2014

### rem45

How would one find the velocity of this electron. Is it considered relativistic or will 1/2mv^2 work just fine??

2. Aug 26, 2014

### Staff: Mentor

I think most people would consider this to be non-relativistic. 1.5 keV is much less than the electron's rest-energy which is 511 keV. If you have a little time you can calculate it both ways and see for yourself how much (or rather, how little) difference it makes.

Actually, to find the wavelength (which is what you asked about in the thread title), you don't even need the velocity. What you really need is the momentum.

If you want to do it relativistically, there's a formula that connects energy, momentum and mass, without using the velocity... have you seen it?

There's also a non-relativistic formula connecting kinetic energy, momentum and mass, which you can easily derive by combining the usual formulas for KE and momentum.

Last edited: Aug 26, 2014