# A photon and electron collision

1. Mar 21, 2014

### feliciasutanto

1. The problem statement, all variables and given/known data
Consider a photon colliding with an electron and scattered directly backward. If the electron is initially at rest and the incident photon has frequency f, determine the frequency of the back-scattered photon

2. Relevant equations

3. The attempt at a solution
Since the photon has no rest mass, then it should always move in speed of light. Therefore the frequency before and after the collision must be the same.

2. Mar 21, 2014

### vela

Staff Emeritus
So red light and blue light, both of which travel with speed $c$, have the same frequency and wavelength?