Question

How does the speed of light determine the optical density of a medium?

Answer 1

Refractive index of a medium is defined as:

$R.I=\frac{Speedoflightinair/vacuum}{Speedoflightinmedium}=\frac{c}{v}$

The index of refraction value of a material is a number that indicates the number of times slower that a light wave would be in that material than it is in a vacuum.

So as the index of refraction value increases, the optical density increases, and the speed of light in that material decreases.