Question

A certain prism is found to produce a minimum deviation of ${38}^{\circ }$. It produces a deviation of ${44}^{\circ }$ when the angle of incidence is either ${42}^{\circ }$ or ${62}^{\circ }$ . What is the angle of incidence when it is undergoing minimum deviation?

• A. ${45}^{\circ }$
• B. ${49}^{\circ }$
• C. ${40}^{\circ }$
• D. ${55}^{\circ }$

Answer 1

The correct option is B ${49}^{\circ }$

$\delta =i+e-A$
$\Rightarrow 44=42+62-A\Rightarrow A=104-44={60}^{\circ }$
Also, ${\delta }_m=2i-A$
$\Rightarrow 38-2i-60$
$i=\frac{98}{2}={49}^{\circ }$
So, option (B)