Question

Angle of prism is 30° and its refractive index is √2 and one of the surfaces is silvered. At what angle of incidence, a ray should be incident on one surface so that after reflection from the silvered surface, it retraces its path

(a)  30°

(b)  60°

(c)  45°

(d)  sin^-1 √1.5

Answer 1

Correct option (c)  45°

Explanation :

To retrace path, pt will falt along the normal on second surface 

so r₁ + r₂ = A

and r₂ = 0

Hence r₁ = 30°

n₁ sin i = n₂ sin r  

⇒ sini = (√2)(1/2)

i = 45°