Do photons have mass experiment?

[ehild]

Another question is - can they be said to have kinetic energy? The standard formula for kinetic energy being 1/2mv^2 which of course becomes 1/2mc^2

In Special Relativity, the kinetic energy of a particle is defined as KE=mc²-m₀c² where m₀ is the rest mass. That is zero for a photon, so its KE equal to its energy, KE=mc²=hf.

ehild

 

[WannabeNewton]

Correct me if I am wrong but I don't think that there is such a thing as a photon which is at rest.

Indeed. In order to define an object "at rest" in special relativity, we must first construct an inertial frame and then define an object "at rest" simply as one whose velocity relative to this frame vanishes. As a consequence of one of the fundamental postulates of special relativity, there exists no inertial frame in which light has vanishing speed hence the notion of "at rest" in the above sense does not apply to light.