Question

 What is meant by the refractive index of a substance?

Answer 1

If i is the angle of incidence and r is the angle of refraction, we get: 

`sin i/sin r` = constant 
This constant value is called the refractive index of the medium in which light enters through air. Refractive index of a medium can also be expressed in terms of speed of light as follows:

₁n₂ =`"speed of light in medium 1"/"speed of light  in medium 2"`
Here, ₁n₂ is the refractive index of medium 2 with respect to medium 1.