In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of the electromagnetic radiation it is also the force carrier for electromagnetic force.
The effect of this force are easily observable at both the levels i.e., microscopic and macroscopic because photon has no rest mass; this allows for interaction at long distances. The modern concept of the photon was gradually developed by ALBERT EINSTEN to explain experimental observations that did not fit the classical wave model of light. In particular, the photon model accounted for the frequency dependence of light’s energy.
DOES THE PHOTON HAVE MASS? AFTER All, IT HAS ENERGY AND ENERGY IS EQUIVALENT TO MASS.
In special relativity, it turns out that we are still able to define a particle’s momentum “r” such that it behaves in well-defined ways that are an extension of the Newtonian case. Although “r and v” still point in the same direction, it turns out that they no longer proportional; the best we can do is to relate them via the particle’s “relativistic mass” mrel.
r = mrel v
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It also turns out that in special relativity, we are able to define the concept of ‘energy’ E such that E has simple and welt defined properties just like those it has in Newtonian mechanics.
When a particle has been accelerated so that it has some momentum r(length of vector r) and relativistic mass mrel. Then its energy E turns out to be given by
E = mrel. C sq., and also E sq. = r sq. c sq. + m sq. rest c raise to the power 4
Like wise the behavior of static magnetic fields would be modified. An upper limit to the photon mass through satellite can be inferred through satellite measurements of planetary magnetic fields with high certainty. The charge composition explore spacecraft was used to derive an upper limit of 6*10 raise to the power –16 eV. This was slightly improved in 1998 by Roderick lakes in a laboratory experiment that looked for anomalous forces on a Cavendish balance. The new limit is 7*10 raised to power –17 eV. Studies for galactic magnetic fields suggest a much better limit of less than 3*10 raised to the power –27 eV but there is some doubt about the validity of this method
