# Does a Photon Have Momentum?

*Most recent answer: 09/10/2012*

Q:

photon have zero rest mass how can it possiable its momemtum

- pintukumaryadav (age 18)

purnia bihar india

- pintukumaryadav (age 18)

purnia bihar india

A:

Yes it does. Although the photon has zero rest mass, it does have energy. From the relativistic relationships among Energy, Mass, and Momentum, E

Even in classical electromagnetic theory a traveling wave caries energy and momentum in the same ratio.

LeeH

^{2}= (M_{o}c^{2})^{2}+ (pc)^{2}, if the rest mass is zero then the momentum is give by p = E/c. Consider a photon bouncing directly back from a small mirror. It is observed by direct experimental measurement that if a laser beam is reflected from a mirror, the mirror will recoil with the same amount of momentum that the photon had (minus a tiny amount do the slight wavelength shift in the recoiling photon).Even in classical electromagnetic theory a traveling wave caries energy and momentum in the same ratio.

LeeH

*(published on 09/10/2012)*