Manipal Entrance Test 2013 Physics Paper

In the position of minimum deviation angle of incidence is equal to angle of emergence
Let a ray of monochromatic light PQ be incident on face AS. PQRS is path of light ray,
where i is angle of incidence r angle of refraction, r angle of incidence and i angle of emergence.
In position of minimum deviation
i′=i,r′=r,δ=δm
2r=A or r=

A

2

Given A = 60°,
r=

60°

2

=30°
Also from Snell's law
µ=

sin‌i

sin‌r

=

sin‌i

sin‌30°

√2=

sin‌i

sin‌30°

⇒ sin‌i=√2×

1

2

=

1

√2

⇒ i=45°