# Conservation of Energy/momentum in Photoelectric process

1. Sep 1, 2011

### Ambidext

1. The problem statement, all variables and given/known data

Show that a free electron cannot absorb a photon and conserve both energy and momentum in the process. Hence, the photoelectric process requires a bound electron. (Eisberg and Resnick 2nd Ed)

2. Relevant equations

hv = E
p = K / c
E2 = (pc)2 + (m0c2)2

3. The attempt at a solution

I've simply shown since
E2 = (pc)2 + (m0c2)2,

rest energy of a moving electron isn't zero and thus energy and momentum cannot be conserved. Is this argument true/suffice?

Last edited: Sep 1, 2011
2. Sep 1, 2011

### vela

Staff Emeritus
I don't see how the conclusion follows from the premise, and I suspect you don't either since you asked if the argument was true.

3. Sep 1, 2011

### Ambidext

How/where then should I start?

4. Sep 2, 2011

### vela

Staff Emeritus
Start by writing the equations for the conservation of energy and momentum the electron and photon would have to satisfy.