Case: Read the following passage and answer accordingly

Total internal reflection is the phenomenon of the reflection of light into a denser medium at the interface of a denser medium with the rarer medium. For this phenomenon to occur necessary condition is that light must move from denser to rarer and the angle of incidence in the denser medium must be greater than the critical angle for the pair of media in contact. Critical angle depends on the nature of the medium and wavelength of light. We can show that µ=1/sinC (where C is the critical angle).

The critical angle for glass-air interface, where µ for glass is 3/2, is

42°

Refractive index is 3/2.

sin θ_c = 1/μ   (sinθ_c critical angle)

         = 1/(3/2)

         = 2/3

     θ_c = sin^-1(2/3) = 42°