(a) Necessary conditions for total internal reflection to occur are:
(i) The incident ray on the interface should travel in optically denser medium.
(iii) The angle of incidence should be greater than the critical angle for the given pair of optical media.
(b)μ=1sinC∘μ0=1sinC
Where a and b are the rarer and denser media respectively. C is the critical angle for the angle for the given pair of optical media