Do Photons have Mass?
We know that Photon is a packet of energy and anything that has energy will have mass (from energy-mass relation), but nothing that has mass should reach speed of light (from Relativity), obviously Photons do travel with speed of light. How is this possible. All this is a confusing loop of paradox statements, do you know the answer to this question.
Wait there is one more thing, Rest Mass & Relative Mass. 'Rest Mass' is mass measured by an observer with respect to whom the object is at rest and 'Relativistic Mass' is mass of object which is in motion relative to observer (Object will acquire mass due to velocity).
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1 solution
From the Special theory of relativity we have
and
Here E = Total Energy of the object,
p = Momentum of the object,
m rest = Rest mass,
m rel = Mass of the object traveling with v velocity,
c = Speed of the light
Since the photon cant have any other velocity than velocity of light (not even zero) and nothing in the universe other than light can travel at that speed the term 'Rest Mass' is not a valid term for light, so equating Rest mass to zero in the above equation we get
after substituting for 'p' and 'v = c' in the above equation we get
=>
So the photon has relativistic mass equal to the ratio of its energy to the square of speed of light and no rest mass.