Question

In the adjacent diagram, AO is a ray of light incident on a rectangular glass block.
(a) Complete the path of the ray till it emerges out of the block.
(b) In the diagram, mark the angles of incidence (i) and the angle of refractive index of glass related to the angles and ?
(c) Mark angles of emergence by the letter e. How are the angles I and e related?
(d) Which two rays are parallel to each other? Name them.
(e) Indicate in the diagram the lateral displacement between the emergent ray and the incident ray.

Answer 1

Hint: A rectangular glass slab is a transparent medium which lets light refract through it. Bending of light takes place after refraction. The glass has some refractive index due to which speed of light changes when the medium changes. Due to the presence of glass slab in the path of light, the light gets shifted from its path.

Complete answer:
The glass slab refraction follows the laws of refraction.
The refraction of light is a property of light in which the light changes its path or bends when it passes from one medium to the other. This phenomenon occurs in prism, glass slab and other transparent or translucent materials.
When the incident ray enters the glass slab (kept in air) it bends towards the normal because light travels from rarer medium to denser medium. After the refraction, inside the glass slab the light ray will bend away from the normal since the light is moving from denser medium to rarer medium.
Following are the laws of refraction:
The incident ray, the normal ray, and the refracted ray, all lie in the same plane.
Snell’s law: The law states that the ratio of the sine of an angle of incidence to the sine of the angle of refraction is constant.
$${\displaystyle \frac{Sini}{Sinr}}=Cons\mathrm{tant}$$
(a)

The path of the ray is completed.
(b) The angle of incidence, the angle of refraction and the emergence angle is marked in the above diagram.
(c) The angle of emergence is marked by letter e. According to the alternate interior angles, the angle of incidence should be equal to the angle of emergence.
$$angle(i)=angle(e)$$
(d) The incident ray and the emergent ray are parallel to each other. These rays are parallel in all the possible cases in a glass slab. The outer medium where the glass slab is placed does not matter.
(e) The lateral displacement is shown in the figure. It is defined as the perpendicular shift in the path of light when it emerges out from the refracting medium. This distance is measurable if we know the thickness of the slab and the angles predefined.

Note:
As the light is travelling from rarer to denser optical medium, ray bends towards the normal and the angle of refraction will be lesser than the angle of incidence. When light passes from denser medium to rarer medium then it bends away from the normal so angle of refraction is greater than angle of incidence.