\(m=\frac {m_{0}}{\sqrt {1-\frac {v^{2}}{c^{2}}}}\)

As speed of light changes in a medium, should we change the denominator also?

If we dont change the denominator, then for a photon travelling with a high fraction of speed of light in a medium (less than c), mass should be defined, but it is not.

## Comments

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TopNewestThe speed of the photon is same regardless of the medium.

It is it's apparent speed that we observe (which is lower due to collisions with the particles of the medium).

Note:This argument holds for any mass less particle as well. – Deeparaj Bhat · 4 weeks agoLog in to reply

– Prince Loomba · 3 weeks, 6 days ago

The 2nd is not. Obvio the first isLog in to reply

– Deeparaj Bhat · 3 weeks, 6 days ago

I'm sorry, I don't understand what you're saying.Log in to reply

– Prince Loomba · 3 weeks, 6 days ago

I am saying the first point is valid for all, for all particles it should be such. But the second point is for photon speciallyLog in to reply

– Prince Loomba · 3 weeks, 6 days ago

As I am saying mass should be defined, which is not only in photon's caseLog in to reply

– Deeparaj Bhat · 3 weeks, 6 days ago

Mass of what? The rest mass of the photon is zero. And the above formula is consistent with the fact that the moving mass of a photon is not defined.Log in to reply

– Prince Loomba · 3 weeks, 6 days ago

If we change it according to refractive index, then only mass of photon will be undefined in all cases. Thats my pointLog in to reply