Question

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

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

Answer 1

Answer: (B)

${49}^o$

Given minimum deviation of the prism ${\delta }_m$=${38}^0$

Also angle of incidence =${42}^0$ and emergent ${62}^0$ and deviation $\delta$=${44}^0$

Since we know deviation $\delta =(i+e)-A$ where A is refraction angle of prism

$A=(42+62)-44=60$

Now ${\delta }_m=2i-A$

$i=\frac{{\delta }_m+A}{2}$

$i={49}^0$