Question

Define absolute refractive index of a medium and relative refractive index.

Answer 1

Absolute refractive index of a medium is defined as the ratio of the velocity of light in vacuum to the velocity of light in the medium. If c is the velocity of light in vacuum and v in the medium, then n = c/v.

The relative refractive index between a pair of media is the ratio of their absolute refractive indices. While the absolute refractive index of any material medium is always greater than unity, its relative refractive index may be greater or lesser than unity.