Write laws of refraction. Explain the same with the help of ray diagram, when a ray of light passes through a rectangular glass slab
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.
