Photon Mass and Momentum

Most recent answer: 07/31/2015

Q:
if the rest mass of photon is zero,then its mass during its motion with the speed of light should also be zero(according to einstein's eqn.of mass variation), but it is not because it has some momentum during motion.....but how?
- osama (age 19)
islamabad,pakistan
A:

We've dealt with this before:

Mike W.


(published on 07/31/2015)