Define refraction and state the laws of refraction.

Definition: The phenomenon of change in the direction of light when it passes from one transparent medium to another is called refraction. 

The laws of refraction can be stated as follows:

(a) The incident ray and the refracted ray are on the opposite sides of the normal at the point of incidence and all three lie in the same plane. 

(b) For a given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. 

i.e. sin i / sin r = constant

Where, i = angle of incidence, 
r = angle of refraction.