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.

Explanation

Law 1 : The incident ray, the refracted ray and the normal at the point of incidence, at the interface of the two transparent media, all lie in the same plane.
Law 2 : The ratio of sine of angle of incidence (sin i) to the sine of angle of refraction (sin r) is a constant, for the light of a given colour and for the given pair of media. This true for angle `0 lt i lt 90^(@)`.
`(sin i)/(sin r)=` constant `= mu`
This constant value `mu` is called the refractive index of the medium.
Let a ray of light travel from air to a material medium.
Let Speed of light in air = c
Speed of light in medium = v
Refractive index of medium with respect to air
`= mu =("speed of light in air")/("speed of light in medium")=(c )/(v)`
This is called the Absolute refractive index of medium.