Question

The angle between the incident ray and the emergent ray in a glass prism is called as
A. Angle of emergence
B. Angle of reflection
C. Angle of refraction
D. Angle of deviation

Answer 1

Hint: Refraction through a prism occurs when light passes from a lighter medium to the denser medium. The angle at which the incident ray passes through the surface of the prism to the normal is called an incident angle and the angle by which the ray emerges out of the prism to the normal is called an emergent ray. These two rays make an angle due to the refraction happening at the surfaces of the prism. This angle can find out from the incident angle, emergent angle and angle of prism.

Complete step-by-step answer:

A prism is a wedge-shaped portion of a transparent refracting medium bounded by two plane faces inclined to each other at a certain angle. Triangle ABC represents the principle section of the prism. When a ray of light enters from lighter medium to denser medium it bends towards the normal. Here the air is lighter medium and prism is denser medium. As the ray moves out of the prism it again undergoes refraction on moving from denser medium to lighter medium. This time, the refracted ray bends away from the normal.
The angle of deviation δ is the angle between the incident ray and emergent ray. It can be understood clearly from the figure. Deviation produced by the prism can be expressed as,
$\begin{align}
  & \delta =(\text{i + r) - A } \\
 & \text{i = incident angle} \\
 & \text{r = Emergent angle from the prism} \\
 & \text{A = Angle of the prism or refracting angle} \\
\end{align}$

When a ray of light is refracted through a glass prism the sum of angle of incidence and angle of emergence is equal to the sum of angle of deviation produced and the angle of the prism.
From the equation mentioned above, we can understand that angle of deviation $(\delta )$ is the angle between the incident ray and emergent ray. Therefore, option D is the correct answer.

Additional information:
The angle of deviation produced by a light ray depends on 4 factors: -
(1) incident angle
(2) The material of the prism
(3) The wavelength of light used
(4) The angle of the prism

Note: The minimum value of angle of deviation suffered by a ray on passing through a prism is called an angle of minimum deviation. Denoted by ${{\delta }_{\text{min}}}$. The deviation produced by the prism is maximum when either the angle of incidence or angle of emergence is $\text{90}{}^\circ $. This is known as the grazing angle. At this condition, either incident ray or emergent ray will graze along the surface of the prism.