A rectangular glass slab ABCD (refractive index 1.5) is surrounded by a transparent liquid (refractive index 1.25) as shown in the figure. A ray of…

For glass-liquid interface: $\displaystyle \sin i_{c}=\frac{1}{n_{21}}$ $\displaystyle =\frac{1.25}{1.5}$ $\displaystyle =\frac{5}{6}$ $\displaystyle i_{c}+r=90^{\circ}$ $\displaystyle \sin r=\sqrt{1-\cos ^{2} r}=\frac{\sqrt{11}}{6}$ Since $\displaystyle \frac{\sin i}{\sin r}=n$ Therefore $\displaystyle \sin i=\frac{\sqrt{11}}{4}$ or $\displaystyle i=\sin ^{-1} \frac{\sqrt{11}}{4}$