Question

Rest mass of a photon is _______.

Answer 1

Photon:

On the basis of Einstein's quantum theory light propagates in the form of packets, that is quanta of energy, which is called a photon.

Rest mass of the photon

The rest mass of photons is being zero.

On the basis of the relativistic theory equation, the mass of the photon is

$$\begin{gathered} m=\frac{m_0}{\sqrt{1-{\displaystyle \frac{v^2}{c^2}}}} \\ {m}_0=m\sqrt{1-\frac{v^2}{c^2}} \end{gathered}$$

when $v=c=3\times {10}^{8}m/s$ (The photons move with the speed of light)

So, $m_0=0$

where $m_0$ is the rest mass of the photon,

$m$ is the classical mass of a particle,

$v$ is the velocity of the particle,

$c$ is the speed of light.

Hence, the rest mass of the photon is zero.