Question

How can photons have no mass and yet still have energy given that E=mc2E=mc2?

Answer 1

You can solve E=mc2E=mc2 for particles that can be brought to rest. This equation is only valid when the particle is at rest. It is a special case of the more general equation, E2=(mc2)2+(pc)2E2=(mc2)2+(pc)2, where pp is the particle's momentum.

A photon cannot be brought to rest. It has no rest mass. But it has momentum. So for the photon, another special case of the above equation applies: E2=(pc)2E2=(pc)2 or E=pcE=pc. Just as E=mc2E=mc2 is only for massive particles that are at rest, E=pcE=pc is only for massless particles that move at the speed of light.

hope u got it (-:

Answer 2

photons do not have mass