Question

A small angled prism of angel $3^{\circ }$ is made of material having refractive index $\mu =1.5$. A ray of light is incident as shown in the figure. $M$ is a plane mirror. Find the angle of deviation for the ray reflected from the mirror $M$ w.r.t. the incident ray.

• A. ${175}^{\circ }$
• B. ${178.5}^{\circ }$
• C. ${170}^{\circ }$
• D. ${150}^{\circ }$

Answer 1

The correct option is B ${178.5}^{\circ }$


As we know, for small angle prism, deviation is given by

$s_1$ = $(\mu -1)A$

$\Rightarrow s_1=(1.5-1)\times 3={1.5}^{\circ }$

Now, deviation of ray due to mirror $M,$,

$s_2={180}^{\circ }-2s_1$

$\Rightarrow s_2={180}^{\circ }-(2\times 1.5)={177}^{\circ }$

So, total deviation $s$ will be

$s=s_1+s_2={1.5}^{\circ }+{177}^{\circ }={178.5}^{\circ }$

Hence, option $\left(b\right)$ is correct.