A ray of light incident at an angle theta on a refracting . . .

Question : A ray of light incident at an angle θ on a refracting face of a prism emerges from the other face normally. If the angle of the prism is 5° and the prism is made of a material of refractive index 1.5, the angle of incidence is 

a) 7.5°

b) 5°

c) 15°

d) 2.5°

Doubt by Saif

Solution :

Here

Refractive Index of Prism (µ) = 1.5
Angle of Prism (A) = 5°

Angle of incidence (i) = θ

Here, r₂=e=0°

We know, 
r₁+r₂=A
r₁+0°=5°
r₁=5°

Applying Snell's Law 
µ=sini/sinr

µ=i/r [∵ Since Angles are small]
µ=θ/r1
1.5=θ/5°
7.5°=θ

θ=7.5°

Hence, a) 7.5°, would be the correct option.