Question

A ray of light passes through an equilateral prism such that an angle of incidence is equal to the angle of emergence and the latter is equal to $ \frac{3}{4}\text{th} $ the angle of prism. The angle of deviation is

• A. $45^{\circ}$
• B. $39^{\circ}$
• C. $20^{\circ}$
• D. $30^{\circ}$

Answer 1

Answer: (D)

Angle of incidence $=$ angle of emergence
ie, $i=i$
Also, $i=\frac{3}{4} \times$ angle of equilateral prism
$=\frac{3}{4} \times 60^{\circ}$
$=45^{\circ}$
Thus, angle of deviation $=i+i-A$
$=\left(45^{\circ}+45^{\circ}-60^{\circ}\right)$
$=30^{\circ}$