Figure shows the section of a semi-circular glass slab having its centre at O. three rays of light A,B and C of the same colour are incident on the slab and strike on the edge XY at the point O. the light ray B suffers refraction along OB'.

(a) On the diagram, mark the critical angle by C.
(b) The rays enter the slab undeviated. give reason.
(c) Draw the path of rays A and C after they strike the edge XY.
(d) Name the phenomenon which the rays A and C exhibit.

Explanation

(a) In figure, the critical angle has been marked as C which is the angle of incidence for the ray B.

(b) Each of the rays A, B and C is incident normally on the slab along its radius, so it enters the slab undeviated.
(c) Figure shows the path of the rays A and C after they strik the edge XY and OA. and OC. respectively.
(d) The ray A suffers refraction from glass to air while the ray C suffers total internal reflection.