Ans. Laws of reflection are as follows:

(a) The incident ray, the refracted ray and normal at the point of incidence; all lie in the same plane.

(b) The ratio of sine of incidence to sine of refraction is a constant, for the light of a given colour and for a given pair of media. This law is also called Snell’s Law.

• ABCD is a glass slab. EF is incident ray which is incident on point O on air-glass interface.

• NO is normal and ∠ EON  = ∠ i ; which is angle of incidence.

• N’O’ is normal extended towards the glass slab

and 1 ∠ = ∠ N OO r ' ; which is angle of refraction.

• OO’ is refracted ray from surface AB. It behaves like incident ray on surface CD.

• MO’ and O’M’ are normal on surface CD.

• GH is the emergent ray.

• ∠ OO M = ∠  i₂ ' ; which is angle of incidence at surface CD.

•  ∠ MO H = ∠ r₂ ' ; which is angle of refraction at surface CD.

• It is observed that EF, NO and OO’ lie in the same plane; which is in accordance to the first law of refraction.

• It is also observed that EF  ǁ GH ; which means emergent ray is parallel to incident ray.

This happens because the degree of bend at opposite surfaces of glass slab is same.