If the refractive index of air with respect to glass is expressed as $^g\mu_a = \dfrac{\text{sin i}}{\text{sin r}}$ answer the following:

(a) Express the similar expression for $^a\mu_g$ in terms of i and r.

(b) If angle r = 90°, what is the corresponding angle (i) is called?

(c) Write down the physical significance of angle (i) in part (b).

(a) The expression for _aμ_g = $\dfrac {\text {sin r}}{\text {sin i}}$

(b) When refractive angle r = 90° then, the corresponding angle of incidence i will be equal to critical angle.

(c) The phenomenon of total internal reflection occurs when the angle of incidence exceeds the value of i obtained in part (b).