The refractive index determines how much the path of light is bent, or refracted, when entering a material.This is described by Snell's law of refraction, n 1 sin θ 1 = n 2 sin θ 2, where θ 1 and θ 2 are the angle of incidence and angle of refraction, respectively, of a ray crossing the interface between two media with refractive indices n 1 and n 2.

Diamond has a very high refractive index (about 2.42 compared to about 1.5 for glass). The amount of light reflected at an air/whatever interface is related to the refractive index change at the interface, and generally speaking the bigger the refractive index change the more light is reflected.

The refractive index of diamond is 2.42. What is the meaning of this statement ? The refractive index for diamond is approximately 2.42, this means the speed of light in diamond is approximately 2.42 times slower than the speed of light in air.

The refractive index of diamond is `2.47` and that of glass is `1.51`. How much faster does light travel in glass than in diamond ?

The refractive index of water = Speed of light in air / Speed of light in water. Given : Refractive Index = 4 / 3. Speed of light in air = 3 * 10⁸ m/s. We have to find Speed of light in water. Substituting the values in the formula for refractive index : refractive index of water = Speed of light in air / Speed of light in water. 4 / 3 = 3.