A prism is made of glass of unknown refractive index. A parallel beam of light is incident on a face of the prism. By rotating the prism the minimum angle of deviation is measured to be $40 ^{\circ}$ The refractive angle of the prism is $60^{\circ}$ If the prism is placed in water (refractive index 1.33) predict the new minimum angle of deviation of a parallel beam of light

Question

$\begin{array}{1 1} 15^{\circ} \\ 30^{\circ} \\ 20^{\circ}20' \\ 10^{\circ} 20' \end{array}$