Question

A ray of light is incident at an angle of 60° on one face of a prism of angle 30°. The ray emerging out of the prism makes an angle of 30° with the incident ray. The emergent ray is

• A. Normal to the face through which it emerges
• B. Inclined at 30° to the face through which it emerges
• C. Inclined at 60° to the face through which it emerges
• D. None of these

Answer 1

The correct option is A Normal to the face through which it emerges

Angle of incidence, i = 60°
Angle of prism, A = 30°
Angle of deviation, δ = 30° [Angle between incident ray and emergent ray = 30°]
Angle of emergence, e = ?
Now, $\delta =i+e-A$
$\Rightarrow {30}^o={60}^o+e-{30}^o$
$\Rightarrow e=0^o$
Thus, the emergent ray will be normal to the face of the prism.
Hence, the correct answer is option (a).