Question

The refraction of light by a prism is shown in the following figure. Then angle D is-

A. Angle of prism
B. Angle of refraction
C. Angle of emergent
D. Angle of deviation

Answer 1

A ray of light that strikes a surface is called an incident ray. The angle between the incident ray and the normal to the surface is called the angle of incidence.When an incident light ray passes through the second medium its direction changes, the ray is said to be a refracted ray and the angle between the refracted ray and the normal is called the angle of refraction.

Complete answer:
The incident ray of light gets refracted towards the normal when it enters the prism. On striking the other face of the prism, the refracted ray further deviates away from the normal and leaves the glass prism; it enters the air i.e. from one medium to the other. Thus a ray that emerges from the other side of prism is called the emergent ray. The angle made by the emergent ray with the normal at the surface is known as angle of emergence.
In the figure see that the emergent ray is extended backward and the incident ray is produced forward, so the angle between these two rays shows the amount of deviation of the incident ray and is thus called the angle of deviation.Therefore the angel mentioned in the question i.e. angle D is angle of deviation.

Hence, option D is the correct answer.

Note: When a ray travels from rarer medium to a denser medium it bends towards the normal and when a ray travels from denser to a rarer medium it bends away from the normal. At an angle of minimum deviation of the prism the refracted ray becomes parallel to the base of the prism.