The refractive index of air with respect to glass is expressed as

${}_g{\mu }_a={\displaystyle \frac{\text{sin i}}{\text{sin r}}}$gμa = \dfrac {\text {sin i}}{\text {sin r}}

(a) Write down a similar expression for _aμ_g in terms of the angles i and r.

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

(c) What is the physical significance of the 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).