Question

A ray of light incident at an angle $\theta$ on a refracting face of prism emerges from the other face normally. If the angle of the prism is $5$ and the prism is made of material of refractive index $1.5$, the angle of incidence is

• A. ${7.5}^{\circ }$.
• B. $5^{\circ }$.
• C. ${15}^{\circ }$.
• D. ${2.5}^{\circ }$.

Answer 1

The correct option is A ${7.5}^{\circ }$.

We have deviation, $\delta =(M-1)A$

$\delta =(1.5-1)5^{\circ }={2.5}^{\circ }$

The angle of the prism is 50°.The ray emerges from refracting face of a prism normally.

Then, $i_2=r_2=0$

As, $A=r_1+r_2=0$

$r_1=A$

$r_1=50°$

But $i_1=\mu r_1=\frac{3}{2}\times 5=7.5°$