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

(i) What will be the angle of emergence?

(ii) If the angle of incidence is changed to (a) 30°, (b) 60°, state in each case whether the angle of deviation will be equal to less than or more than 36°?

(i) As we know that in an equilateral glass prism the ray suffers minimum deviation.

So, angle of incidence i₁ is equal to angle of emergence i₂

Given, angle of incidence i₁ = 48°

Applying the rule given above, we get,

    i₁ = i₂
⇒ i₂ = 48°

Hence, angle of emergence i₂ = 48°

(ii) (a) As the minimum angle of deviation is 36° for yellow light, at an incident angle of 48° so for any angle of incidence other than 48° the angle of deviation will be more than 36°.

Hence, when the angle of incidence is changed to 30°, the angle of deviation will be more than 36°.

(b) As the minimum angle of deviation is 36° for yellow light, at an incident angle of 48° so for any angle of incidence other than 48° the angle of deviation will be more than 36°.

Hence, when the angle of incidence is changed to 60°, the angle of deviation will be more than 36°.