Question

Explain what is a refractive index?

Answer 1

Definition of Refractive Index

1. The Refractive index of a particular medium is defined as the ratio of the speed of light in a vacuum and the speed of light inside that medium.
2. Hence, the refractive index is a characteristic property of a medium.
3. The Refractive index of vacuum is unity.
4. The Refractive index is a dimensionless quantity.
5. The Refractive index gives the amount of refraction occurring when a light ray is traveling from one medium to another medium.

Snell's Law

Snell's law states that, for a given pair of media, the ratio of the sines of the angle of incidence $i$ and angle of refraction $r$ is equal to the ratio of refractive indices of the two media.

Let, $n_1$ and $n_2$ be the refractive indices of the two media then

$\mu =\frac{\sin i}{\sin r}=\frac{n_2}{n_1}$

Hence, the refractive index is also defined as the ratio of the sine of the angle of incidence and the sine of the angle of refraction.

Schematic Diagram

Mathematical Expression

The Refractive index is given as,

$\mu =\frac{c}{v}=\frac{\sin {\theta }_1}{\sin {\theta }_2}$

where $c$ is the speed of light in a vacuum,

$v$ is the speed of light in a medium,

${\theta }_1$ is the angle of incidence,

${\theta }_2$ is the angle of refraction.