Question

What is the refractive index of a medium?

Answer 1

The index of refraction is the ratio of the speed of light in a vacuum compared to the speed of light in the medium. The index has been given a value of 1 for a vacuum. Light travels fastest in a vacuum compared to any other medium, so the indicies of refraction will be greater than 1 for any other medium

Answer 2

Specifically the index of refraction for a medium is defined as:\[n=\frac{ c }{ v }\]where n is the index of refraction of the medium; c is the speed of light in a vacuum; and v is the speed of light in that medium.

Answer 3

If you want an electromagnetic explanation, the index of refraction is defined as:\[n=\sqrt{\epsilon _{r}\mu _{r}}\]where εr is the relative permitivity of the material; and μr is the relative permeability of the material.