An engineer intends to deviate a light ray from its path by 120° through reflection from a plane mirror. Calculate the angle of incidence?

A. 60°
B. 40°
C. 30°
D. 20°

Correct Answer:

Option C – 30°

Explanation

Angle of deviation = 180 – [i + v]
= 180 – 2i [since i = v]
∴ 120 = 180 – 2i
2i = 180 – 120
= 60
∴ i = 30°