Question

Define relative refractive index

Answer 1

Relative refractive index of medium(N) is the ratio of the speed of light in a specified medium(M) to that in the given medium(N).

In absolute refractive index(or simply refractive index), the specified medium(M) is vacuum. So if you take any other medium instead of vacuum as the specified medium, you will get relative refractive index.

Answer 2

The ratio of the speeds of light , in a given pair of media, gives us a measure of the extent of refraction (or bending) of a ray of light as it goes from one of these media to the other. We use this ratio to define a term called the RELATIVE REFRACTIVE INDEX for a given pair of media.

⇒2/1u = Speed of light in medium 1 / Speed of light in medium 2 = V1 / V2

The refractive index, or absolute refractive index of a medium ( say ,m ) , denoted by $u_{m}$ , is defined as follows :

$u_{m}$ = Speed of light in vacuum / Speed of light in given medium = $\frac{c}{V_{m} }$