Question

P is a small angled prism of angle α = 3° made of a material of refractive index 1.5. A ray of light is incident as shown in Fig. M is a plane mirror. The angle of deviation for the ray reflected from the mirror M with respect to the incident ray is:

(a) 4.5°

(b) 175.3°

(c) 177°

(d) 178.5°

Answer 1

Correct option: (d) 178.5°

Explanation: 

Deviation produced by prism, d₁ = (n – 1)A = (1.5 – 1) x 3° = 1.5° , C.W. 

Angle of incidence on the mirror, i = 1.5°

Deviation produced by mirror, d₂ = (180 – 2i) = 177° , C.W. 

or total deviation, d = d₁ + d₂ = 178.5°