Question

Rest mass of photon is zero but photon possesses mass in a beam of light. Is that true

Answer 1

The statement is true .

Answer 2

The statement is false .

A beam of light is also massless because it is a form of energy and not MASS.

The rest mass of a photon is zero .

Details .

The photon is a light particle .

It is never at rest.

It is always in motion.

Hence rest energy is zero.

Put this in the Einstein's equation :

E² = m²c⁴ + p²c²

When an object is at rest , p = 0 .

Rest energy = 0

⇒ m²c⁴ = E

But c is not 0 .

So rest mass has to be 0.