Question

A beam of monochromatic light is incident at i=50° on one face of an equilateral prism, the angle of emergence is 40°, then the angle of minimum deviation is :

(A) 30° (B) <30° (C) ≤30° (D)≥30°

Answer 1

Step 1: Given

Angle of incident, $i={50}^o$

Angle of emergence, $e={40}^o$

Angle of the prism, $A={60}^o$ (since prism is equilateral)

Angle of deviation, $\delta$

Step 2: Formula used and calculation

$\delta =i+e-A$

$\Rightarrow \delta ={50}^o+{40}^o-{60}^o$

$\Rightarrow \delta ={30}^o$

$\therefore {\delta }_{min}<\delta$

$\therefore {\delta }_{min}<{30}^o$

Hence, option (B) is correct.