Question

A light ray of yellow colour is incident on an equilateral glass prism at an angel of incidence equal to 48° and suffers minimum deviation by an angle of 36°.

1. What will be the angle of emergence?
2. If the angle of incidence is changes to (a) 30°, (b) 60°, state whether the angle of deviation will be equal to, less than or more than 36°?

Answer 1

We know that, ∠A= r₁ + r₂ and i + e = A + δ

1. In position of minimum deviation ∠i = ∠e = 48° and for equilateral Δ,
   ∠A= 60°
   ∵ i + e = A + 8.
   e + e = 60 + 36
   2e = 96
   e = 48° Angle of Emergence

2. We are aware that when the incidence angle increases, the deviation angle first decreases and then reaches the minimum value for a particular incidence angle.

   1. ∠i = 30°, angle of deviation will be greater than 36°
   2. at ∠i = 60°, angle of deviation will be greater than 36°