When light travels from one medium to another, there is a change in its direction due to a change in speed of light.

Laws of Refraction

The incident ray,the refracted ray and the normal to the surface of separation of two media at the point of incidence,all lie in the same plane.

Snell’s law: The ratio of sine of angle of incidence I to the sine of angle of r is constant and is called the refractive index of medium 2 with respect to medium 1


The ratio of the speed of light in first medium (v1) to the speed of light in the second medium (v)

Refraction Through a Glass slab

When a ray of light incident from air from air (rare medium ) on a glass slab (denser medium),it bends towards the normal and it emerges from the glass slab,The emergent ray is parallel to the incident ray but is laterally displaced.The lateral displacement is proportional to the thickness of the glass slab.


1/v -1/u =1/f