Question

The value of angle of deviation produced by a prism varies with an increase in the value of angle of incidence as follows:

• A. As the angle of incidence increases, first the angle of deviation decreases then for a certain angle of incidence, the angle of deviation becomes maximum and then the angle of deviation increases.
• B. As the angle of incidence increases, first the angle of deviation increases then for a certain angle of incidence, the angle of deviation becomes maximum and then the angle of deviation decreases.
• C. As the angle of incidence increases, first the angle of deviation increases then for a certain angle of incidence, the angle of deviation becomes minimum and then the angle of deviation decreases.
• D. As the angle of incidence increases, first the angle of deviation decreases then for a certain angle of incidence, the angle of deviation becomes minimum and then the angle of deviation increases.

Answer 1

Answer: (D)

1. When a ray of light incident on a prism, it suffers refraction from both the inclined surfaces of the prism and emerges as bending towards the base of the prism.
2. ​The angle between the incident ray and the emergent ray is called the angle of deviation($\delta$).
3. If A be the angle of the prism then, $\delta =i_1+i_2-A$ , Where $i_1$ is the angle of incidence and $i_2$ be the angle of emergence.
4. It is found that, when the angle of incidence increases, the angle of deviation decreases, and at a certain value of angle of incidence the angle of deviation attains a minimum value.
5. At the point of minimum angle of deviation, the angle of incidence is equal to the angle of emergence.
6. And again if we continue to increase the angle of incidence, the angle of deviation also increases.

The graph that shows the variation of angle of deviation with the angle of incidence is as follows:

Thus,

Option B) As the angle of incidence increases, first, the angle of deviation decreases then for a certain angle of incidence, the angle of deviation becomes minimum, and then the angle of deviation increases is the correct option.