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

1.	How do you justify that the rest mass of photons is zero ?
Answer» SOLUTION :The mass of a body moving with speed v is `m = m_0/SQRT(1-v^2/c^2)` REST mass`m_0 = m sqrt(1-v^2/c^2)` for a photon v= c, therefore `m_0=msqrt(1-c^2/c^2)=0`

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

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