Question

Four students perform an experiment on tracing the path of a ray of light passing through a rectangular glass slab. Their individual observations are:
Identify the incorrect observations and correct them.
A). Angle of emergence is less than the angle of refraction
B). Angle of emergence is greater than the angle of incidence
C). Emergent ray is parallel to the refracted ray
D). Emergent ray is parallel to the incident ray

Answer 1

Hint: Students must remember that the incident ray and the emergent rays are always parallel to each other after refraction. When light rays go from rarer medium i.e. air to the denser medium i.e. glass the refracted rays bend towards the normal and from denser to rarer it bends away from the normal.

Complete step by step answer:
When a ray of light passes through a glass slab from denser to rarer medium it undergoes double refraction. Once when it enters the glass slab and second time when it leaves the glass slab.

The emergent ray comes out parallel to the incident ray when it leaves the glass slab. This is due to the fact that the ray enters and leaves the two sides of a parallel glass slab. Therefore, emergent ray is parallel to the incident ray is the correct statement. Also, the angle of emergence is equal to the angle of incidence. Since refracted angle is less than the angle of incidence therefore it is also less than the angle of emergence.

The corrected statements are:
Angle of emergence is greater than the angle of refraction
Angle of emergence is equal to the angle of incidence
Emergent ray is not parallel to the refracted ray
Emergent ray is parallel to the incident ray

Note: It should be noted that the emergent ray is always parallel when it leaves the glass slab. This would not have been the case if we used a Prism instead of a glass slab as its two sides where the ray of light enter and leave are not parallel to each other.