# Homework Help: Momentum of photon

1. Sep 22, 2011

### logearav

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

Photon dont have mass. But they possess momentum.

2. Relevant equations

3. The attempt at a solution
Momentum is product of mass and velocity. Then how photons which dont have mass can have momentum?

2. Sep 22, 2011

### Staff: Mentor

Momentum is a product of mass and velocity only for things that have rest mass. For things without rest mass (like photons) another expression holds.
$$p = \frac{h \nu}{c} = \frac{h}{\lambda}$$

3. Sep 22, 2011

### logearav

Thanks gneill for your clarification

4. Sep 22, 2011

### ehild

The momentum of the photon can be written also as p=mc, where m=E/c2. (And E=hν)

ehild