Question

Total Internal Reflection at Glass - Air Surface.

Answer 1

Consider an incident ray going from glass (μ = 1.5) to air. The critical angle of incidence, i_c is

Fig. shows an issoceless right angled glass (refractive index μ) prism. PQ is a ray incident normally at face AB. It goes straight and is incident on face AC at an angle of incident i = 45° . Total internal reflection can occur at R. For T.I.R to take place at face AC, i.e. no light emerges out of face AC, i≥i_c . The minimum value of i; should be equal to i_c . Therefore for T.I.R to take place at face AC

i_min = 45° = i_c

The minimum refractive index μ_m of prism is

Such a glass (μ = 1.5) issocless prism is known as a totally reflecting prism (μ > μ_m). Fig. (a) and (b)

show how such a prism is used to deviate an incident ray by π/2 or π.