Question

A ray of light passes from vacuum into a medium of refractive index n. If the angle of incidence is twice the angle of refraction, then the angle of incidence is:

(A) cos^–1 (n/2) 

(B) sin^–1 (n/2)

(C) 2 cos^–1 (n/2) 

(D) 2 sin^–1 (n/2)

Answer 1

Correct Answer is: (C) 2 cos^–1 (n/2) 

i = 2r

1 sin i = n sin r

⇒ 2 sin i/2 cos i/2 = n sin i/2

⇒ cos i/2 = (n/2)

⇒ i = 2 cos^–1 (n/2)