A monochromatic ray strikes the surface of identical prisms (A, B and C) at different angles of incidence. The diagram below shows their refracted rays. Study the path of these refracted rays and identify in which of the diagrams
(a) the angle of incidence is maximum.
(b) the angle of incidence is minimum.
(c) the angle of incidence is equal to the angle of emergence.
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For a prism, the condition of minimum deviation is special because it's symmetric: angle of incidence (\(i\)) equals the angle of emergence (\(e\)). Visually, this is when the light ray inside the prism is parallel to the prism's base.
(a) The angle of incidence is maximum:
The angle of incidence is maximum in Diagram C. In this diagram, the incident ray is bent the least upon entering the prism (it is furthest from the normal), which corresponds to the largest angle of incidence. (b) The angle of incidence is minimum:
The angle of incidence is minimum in Diagram B. In this diagram, the incident ray is bent the most upon entering the prism (it is closest to the normal), which corresponds to the smallest angle of incidence. (c) The angle of incidence is equal to the angle of emergence:
The angle of incidence is equal to the angle of emergence in Diagram A. This is the specific condition for the angle of minimum deviation. A key feature of this condition is that the refracted ray inside the prism travels parallel to the base of the prism, which is clearly depicted in Diagram A.
