Define refractive index in terms of velocity of light?

Light travels through a glass plate of thickness t and having a refractive index mu .If c is the velocity of light in vacuum,the time taken by the ligth to travel this thickness fo glass is

Define absolute refractive index.

Define modulation index

Find relation for refractive index in terms of real depth and apparent depth.

The refractive index of diamond is:

A convex lens made of material of refractive index n_1 is kept in a medium of refractive index n_1 . Parallel rays of light are incident on the lens. Complete the path of light emerging from the convex lens, if n_1 > n_2