" The rest mass of photon is "

Which of the following is correct regarding photons? (i) A photon always travels at a speed 3xx10^(8)m//sec in vacuum. (ii) The rest mass of photon is zero. (iii) Let E and p be the energy and linear momentum of a photon and v and lambda be the frequency and wavelength of the same light when it behaves as a wave. Then E=h v =(hc)/(lambda) p=(h v)/(c) =(h)/(lambda) =(E)/(c) (iv) A photon may collide with a meterial particle. The total energy and the total momentum remain conserved in such a collision. The photon may get absorbed and / or a new photon may be emitted. Thus, the number of photons may not be consverved.

Assertion : The relative velocity of two photons travelling in opposite directions is C. Reason : The rest mass of a photon is zero .

The rest mass of the photon is

The rest mass of the photon is