IIT JEE , AIEEE Forum - Physics , Mechanics

edison

Agreed with sir cvrmana. Ofcourse speed of light in all the frames whether moving or at rest is c = 300, 000, 000 m/s

I would like to elaborate on the point that photons does not have infinit mass its mass is

m = hf/c^2, where f is frequency of the light of which photon is a quanta.

Momentum is also possessed by photons and momentum of photon is given by P = hf/c

Anything that has momentum ofcourse possess mass and due to momentum only photons exert radiation pressure on the surface on which it falls.

Now coming to ROHITJU's query

anything moving with velocity of light has infinite mass PROVIDED the rest mass of the body is not zero. Thus the concept is not applicable for photons as its rest mass (though photons can never be at rest, remember this and please don't be confused) is zero.

m = m0 / [(1 - v^2/c^2)^2]

where mo is rest mass
and m = mass when body is moving with velocity 'v'

and if mo is NON ZERO then

for v = c or v is comparable to c (limiting case)

m = INFINITE

But the concept fails to explain when applied for photons as

for photons v=c, mo = 0

so m = 0/0 is not defined

Thus we use the concept E = mc^2 = hf

or m = hf/c^2, thus is the mass of photon.

I hope the things are now crystal clear.

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