question_answer

How will you justify that the rest mass of photons is zero?

Answer:

                The mass of a body moving with speed \[\upsilon \] is \[m=\frac{{{m}_{0}}}{\sqrt{1-\frac{{{\upsilon }^{2}}}{{{c}^{2}}}}}\] Rest mass, \[{{m}_{0}}=m\sqrt{1-\frac{{{\upsilon }^{2}}}{{{c}^{2}}}}\] For a photon, \[\upsilon =c,\]therefore, \[{{m}_{0}}=m\sqrt{1-\frac{{{c}^{2}}}{{{c}^{2}}}}=\mathbf{zero}\]