Find the maximum angle of deviation for a prism with angle A = 60° and $μ$ = 1.5.

58°

Maximum Deviation

The deviation is maximum when i = 90° or e = 90° that is at grazing incidence or grazing emergence.

Let i = 90°

$⇒ r_1 = C = \sin^{−1}(1/μ)$

$⇒ r_1 = \sin^{−1}(2/3) = 42°$

$⇒ r_2 = A −r_1 = 60° − 42° = 18°$

$μ \sin g\frac{\sin r_2}{\sin e}=\frac{1}{μ}$

$\sin e = u\, \sin r_2 = 1.5\, \sin 18°$

$⇒  \sin e= 0.463$

$⇒ r = 28°$

Deviation = $D_{max}$

$= i + e – A = 90° + 28° – 60° = 58°$