Question

29.
Fig 4.20
26. In the adjacent diagram, AO is
a ray of light incident on a
rectangular glass slab.
(a) Complete the path of the
ray till it emerges out of
the slab.
(b) In the diagram, mark the
angle of incidence (i) and the angle of refraction
(r) at the first interface. How is the refractive
index of glass related to the angles i and r?
(c) Mark angle 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.
State one factor that affects the lateral
displacement.
tht enters a liguid from air, as
M​

Answer 1

(a) Check attachment for the diagram of glass slab.

Explanation of diagram :-

• A ray of light is incident on the surface of glass slab.
• some of the incident rays gets reflected because 100% refraction is not possible.
• Also, some of the incident rays gets retracted.
• At surface 1 , when refractive takes place light is incident from rarer medium( air) to denser medium ( slab) , therefore refracted ray bend towards normal.
• At surface 2 , when refractive takes place light is incident from denser medium ( slab) to rarer medium( air) , therefore refracted ray bend away from normal.

(b) angle of incidence (i) and the angle of refraction (r) at the first interface is maked in the diagram ( refer attachment).

Now relation between i and r are as follows :-

⟹ n1 sin i° = n2 sin r°

where :-

• n 1 = refraction index of air = 1
• n2 = refraction index of glass slab
• i = angle of incidence
• r = the angle of refraction

⟹ 1 sin i° = n2 sin r°

⟹ ( sin i°) /(sin r°) = n2

(c) angle of emergence is marked in the diagram by e. ( kindly check the attachment).

Relation between i and e :-

angle of incidence = angle of emergence

therefore :- i = e

(d) Incident ray and emergent ray are parallel to each other.

angle of incidence = angle of emergence

(e) Lateral displacement between the emergent ray and the incident ray is indicated in the diagram by LM.

Factors affecting the lateral displacement :-

1. Refractive index of the glass slab
2. The thickness of the glass slab
3. Angle of incident rays.