# Homework Help: Finding wavelength of an electron

1. Jun 30, 2011

### kraigandrews

1. The problem statement, all variables and given/known data
What is the wavelength of an electron with a kinetic energy of 2.00 MeV?

What is the wavelength of an electron with a kinetic energy of 2.08 GeV?

(Possibly useful constants: hc = 1239.8 eVnm, rest energy of the electron: E0,e = 511.0 keV.)

2. Relevant equations
$\lambda$=hc/(2(mc2)K)1/2

3. The attempt at a solution
Should be pretty straightforward, I keep getting the wrong answer though, should just be plug and chug, i would think.

2. Jun 30, 2011

### soothsayer

Are you sure that's a correct equation for the de Broglie wavelength? I've never seen it written that way, though I guess the units do check out...Making sure to put everything in the same units?

I did a rough calculation and you're right, the answers don't seem realistic.

Last edited: Jun 30, 2011
3. Jun 30, 2011

### vela

Staff Emeritus
Your equation for the wavelength is for a non-relativistic electron. Those kinetic energies, however, are greater than the rest energy of the electron, so you're in the relativistic regime.