Define absolute refractive index of a medium
Absolute refractive index of a medium is defined as the ratio of the velocity of light in a 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 value of the absolute refractive index can never be less than 1. This is so because light travels with the fastest speed in a vacuum. The lower value of the absolute refractive index indicates a denser medium while a higher value indicates rarer medium