Question

Dynamic mass of photon in usual notations is given by

Answer 1

What is the dynamic mass of photon?

A photon is known to have no mass as of now. There's only one concept of mass. The invariant mass. For a photon the mass is zero. Concept of relativistic mass is a misleading lesson that beginners in special relativity are taught for them to have an intuitional understanding. But the mass never increases with speed. In practical purposes, scientists use invariant mass or the rest mass as the only mass. But while teaching the beginners dynamic mass or relativistic mass creates a good intuitional understanding. It is the energy and momentum that increases with speed which is given by invariant relation E^2-p^2.c^2=m^2.c^4. In which m is only invariant mass which is the rest mass for any particle. Now since a photon has zero mass, it's energy is given as E=pc.

P.S. It is more beneficial to clarify the misconception “relativistic mass" for a student having interest in studying physics deeply.