Question

(a) Write a relation for the angle of deviation (𝛿) for a ray of light passing through an equilateral prism in terms of angle of incident (i), angle of emergence (e), angle of prism (A).

(b) A ray of light incident at an angle 48^o on a prism of refracting angle 60^o suffers minimum deviation. Calculate the angle of minimum deviation.

(c) A light ray of yellow colour is incident on an equilateral glass prism at an angle of incidence equal to 48^o and suffers minimum deviation by an angle of 36^o. (i) What will be the angle of emergence? (ii) If the angle of incidence is changed to (a) 30^o, (b) 60^o, state whether the angle of deviation will be equal to less than or more than 36^o.

Answer 1

(a) The relation between the angle of incident (i), angle of emergence (e), angle of prism (A) and angle of deviation (𝛿) for a ray of light passing through an equilateral prism is
𝛿 = (i + e) – A

(b) Given,
Angle of incidence, i = 48⁰
Refracting angle, A = 60⁰
Angle of minimum deviation, 𝛿_min =?
We know that
𝛿_min = 2i – A
𝛿_min = 2(48) – 60
𝛿_min = 96 – 60
𝛿_min = 36⁰

(c) (i) In an equilateral glass prism the ray suffers minimum deviation. So
i₁ = i₂
i₂ = 48⁰

(ii) (a) If the angle of incidence is changed to 30⁰, the angle of deviation will be more than 36⁰

(b) If the angle of incidence is changed to 60⁰, the angle of deviation will be more than 36⁰