Question

what is relative refractive index??in many mediums will it occurs??

Answer 1

refractive index is the ratio of sine of angle of incidence to the ratio of sine of angle of refraction.


refractive index = sin I/ sin r

refractive index is always greater than 1. or equal to 1

ya it will occurs in many mediums.
different medium have different refractive index

Answer 2

Refractive index of a medium
    = speed of light in vacuum / speed of light in that medium

Refractive index of vacuum = 1.  Means that there is no refraction in vacuum.

Relative refractive index
      = refractive index of medium 1 / refractive index of medium 2

This is useful when a light ray enters from medium 1 to medium 2 , or the other way round.

For every pair of mediums, there is a relative refractive index.