What is the rest mass of a photon?

Explanation

Mass of a particle in motion is given by
`m = (m_0)/(sqrt(1 - v^2//c^2))`
where `m_0` = rest mass of the particle. Incase of a photon, its velocity is equal to velocity of light.
`therefore " " v = c`
`implies " " m_0 = msqrt(1 - (v^2)/(c^2)) = m sqrt(1 - 1)`
`m_0 = 0`
`implies` Rest mass of a photon is zero.