Question

State the laws of refraction of light. Explain the term ‘absolute refractive index of a medium’ and write an expression to relate it with the speed of light in vacuum.

Answer 1

Hint: Laws of refraction are the rules which light rays follow when they enter from one medium to another medium. Absolute index of a medium is equal to the refractive index of a medium with respect to vacuum.

Complete step by step answer:
 Refraction is the phenomena of bending of light rays when they travel from a medium to another. When light rays travel from one medium to another, they follow some laws that are known as laws of refraction. There are two laws of refraction of light which are:
1. The incident ray, refracted ray and the normal at point of incidence all lie in the same plane.
2. The ratio of sine of angle of incidence and sine of angle of refraction is constant for a given pair of two media, and this constant is equal to ratio of speed of light in two mediums. This law is known as Snell’s law
$\dfrac{\sin i}{\sin r}=\dfrac{{{c}_{1}}}{{{c}_{2}}}$,
Where $i$ is angle of incidence, $r$ is angle of refraction, ${{c}_{1}}$ is speed of light in medium having incident rays and ${{c}_{2}}$is speed of light in the medium receiving refracted rays.
 Absolute refractive index of a medium is defined as the ratio of speed of light in vacuum to speed of light in that medium. Mathematically it can be written as
$\mu =\dfrac{c}{{{c}_{m}}}$ ,
Where $c$ is speed of light in vacuum and ${{c}_{m}}$ is speed of light in that medium
Note: The first law of refraction is almost similar to the first law of reflection. Refractive index of a medium depends on the velocity of light in that medium. If velocity of light in one medium is greater than velocity of light in another medium then the refractive index of the first medium will be smaller than the refractive index of the second medium.