# Define the term refractive index of a medium in terms of velocity of light.

Refractive index is defined as the ratio of the speed of light in a vacuum to its speed in a specific medium.

Refractive index is dimensionless. It is a number that indicates the number of times slower than a light wave would be in the material than it is in a vacuum. Refractive index, represented by symbol n, is the velocity of light in vacuum divided by the velocity of light in a medium. The formula of the refractive index is,

n = c/ν

where

n = Refractive index.

c = Velocity of light in a vacuum ( 3 × 108 m/s).

v = Velocity of light in a substance.

Snell’s law clarifies the relation between the angle of incidence and angle of refraction. So, there are two formulas for calculating the refractive index of a medium. Let us imagine that a ray of light is travelling from a medium a to another medium b. Then conferring from Snell’s law,

$$n = \frac{sin i}{sin r}$$.