Question
(a) Write the necessary conditions for the phenomenon of total internal reflections to occur.
(b) Write the relation between the refractive index and critical angle for a given pair of optical media.Solution
a) Conditions for total internal reflection to take place:
i) Light ray must travel from denser medium into rarer medium.
ii) The angle of incidence in denser medium must be greater than the critical angle for given pair of optical media.
b) Relation between refractive index and critical angle for a given pair is,
As per Snell’s law, 
