Question

How does the index of refraction relate to speed of light?

Answer 1

The refractive index of a pair of media is defined as,

`mu""_(21) = (v""_1)/(v""2)` , where `v""_1` and `v""_2` are the velocities of light in initial and final mediums respectively.
It is read as refractive index of medium 2 with respect to 1.

Similarly, refractive index of a medium can be obtained with replacing `v""_1` with `c` which is equal to the speed of light in vacuum.

Thus refractive index of a medium with speed `v` is given as,

`mu = c/v`