Laws of refraction

(i)                  Incident ray, refracted ray and normal drawn at incident point always lie in the same plane.

(ii)                Snell’s law: For a given colour of light , the ratio of side of angle of incidence to the sine of angle of refraction is a constant,

i.e.  Sin i/ sin r = 1μ₂ (constant)

This constant 1μ₂ is called refractive index of second medium with respect to first medium.

Absolute refractive index of a medium is defined as the ratio so speed of light in free space (vacuum) to that in the given medium.

I.e. absolute refractive index (μ) = speed of light in vacuum 

                                                                                           

                                                  Speed of light in the medium

The refractive index of a medium is different for different colours. The refractive index of a medium decreases with the increase in wavelength of light. Hence refractive index of a medium is maximum fro violet colour of light and minimum for red colour of light.

The refractive index of a medium decreases with the increase in temperature. But this variation is very small.

When a ray of light enters from one medium to other medium, its frequency and phase do not change but wavelength and velocity change.

Some illustrations of Refraction

(i)                  Bending of a linear object when it is partially dipped in a liquid inclined to the surface of the liquid.

(ii)                Twinkling of stars.

(iii)               Oval shape of sun in the morning and evening.

(iv)              An object in a denser medium when seen from a rarer medium appears to be at a smaller distance.

This is way (a) A fish in a pond when viewed from air appears to be at a smaller depth them actual depth (b) A coin at the base of a vessel filed with water appears raised.