Explanation

(a) The ray of light is refracted at the plane surface. However, since the ray is travelling from a denser to a rarer medium, for an angle of incidence (i) greater than the critical angle (c) the ray will be totally internally reflected
For $i < c;$ deviation $\delta = r - i$ with $\frac{1}{\mu} = \frac{\sin i}{\sin r}$
Hence $\delta = \sin^{- 1}{(\mu\sin i)} - i$
This is a non-linear relation. The maximum value of $\delta$ is $\delta_{1} = \frac{\pi}{2} - C$
Where $i = c$ and $\mu = \frac{1}{\sin c}$
For $i > c$, deviation $\delta = \pi - 2i$
$\delta$ decreases linearly with $i$
$\delta_{2} = \pi - 2\ c = 2\delta_{1}$