The rest mass of the photon is

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(A) According to Einstein's quantum theory,light propagates in the form of packets,i.e.,quanta of energy,which are called photons.The rest mass of a p

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$0$

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(A) According to Einstein's quantum theory,light propagates in the form of packets,i.e.,quanta of energy,which are called photons.The rest mass of a photon is zero. This can be shown using the theory of relativity.According to the relativistic mass equation,the mass of a particle is given by:$m = \frac{m_{0}}{\sqrt{1 - \frac{v^{2}}{c^{2}}}}$Rearranging for the rest mass $(m_{0})$:$m_{0} = m \sqrt{1 - \frac{v^{2}}{c^{2}}}$Since a photon always travels at the speed of light $(v = c)$,we substitute $v = c$ into the equation:$m_{0} = m \sqrt{1 - \frac{c^{2}}{c^{2}}} = m \sqrt{1 - 1} = 0$Therefore,the rest mass of a photon is $0$.

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