Question

When an equilateral prism is in minimum deviation position the angle of incidence is:

• A. greater than the angle of emergence
• B. smaller than the angle of emergence
• C. equal to the angle of emergence
• D. none of these

Answer 1

The correct option is C

equal to the angle of emergence

The explanation for the correct answer:

(c) equal to the angle of emergence

• Angle of minimum deviation: The angle between the incident ray produced and the emergent ray produced is called the angle of deviation.
• The angle of deviation decreases with an increase in the angle of incidence.
• A stage comes when for a particular value of angle of incidence, the angle of deviation is minimum.
• It has been found that $\angle \mathrm{A}+\angle \delta =\angle i+\angle \mathrm{e}$, here $\angle A$ is the angle of prism, $\angle \delta$is the angle of deviation, $\angle i$ is the angle of incidence and $\angle e$is the angle of emergence.
• It is found that the angle of deviation decreases with the increase in the angle of incidence.
• A stage comes when for a particular angle of incidence, the angle of deviation is minimum. This position is called the minimum deviation position of the prism. If the angle of incidence is further increased, the angle of deviation starts increasing.
• This occurs only when the angle of incidence is equal to the angle of emergence.

The explanation for the incorrect answer:

(a)greater than the angle of emergence

For the minimum deviation in a prism, the angle of deviation should be equal to the angle of incidence.

(b)smaller than the angle of emergence

For the minimum deviation in a prism, the angle of deviation should be equal to the angle of incidence.

(d) None of these

Option (c) is correct.

When an equilateral prism is in a minimum deviation position the angle of incidence is equal to the angle of emergence. Hence, option (c) is correct.