Question

Explain the term critical angle with the aid of a labelled diagram.

Answer 1

Hint: In order to answer this question, you must be aware of the concept of refractive index. Refractive index is defined as the ratio of the speed of light in a vacuum to its speed in a specific medium.

Complete step by step answer:
 The critical angle is defined as the angle of incidence in the denser medium corresponding to which the angle of refraction in the rarer medium is $90^{\circ}$.

In this case, the refracted ray is perpendicular to the normal.
Angle of incidence is the angle formed between the incident ray and the normal.
Angle of refraction is the angle formed between the refracted ray and the normal.
When a ray of light goes from the rarer medium to the denser medium, it bends towards the normal.

Note: When the refractive index of the two media is equal, then no bending of light occurs. Hence, it is the difference in the refractive index of the two media which causes bending of light. The refractive index of air is 1.0003 and the refractive index of water is 1.33.