Question

A swimming pool appears shallower than its actual depth due to
(A) Reflection
(B) Dispersion
(C) Refraction
(D) Scattering

Answer 1

Hint: To answer this question, we need to trace the path of the light rays as they travel from the swimming pool into the air. We have to remember that the eyes perceive the light rays entering to be travelling straight.

Complete step by step solution:
Let us consider a swimming pool of depth $h$ as shown in the figure below.

Consider that a human eye is observing a point situated at the bottom of the tank, adjusted for near normal viewing. We can see the rays originating from that point. Now, at point C, the light ray changes its leaves to the water medium, which is optically denser, and enters the air medium, which is optically rarer. We know that when the light travels from an optically denser to the rarer medium, it bends away from the normal, as shown in the above figure. The eye receives these bent rays. But it does not perceive the refraction which has taken place. The eye only perceives the light ray to be a straight ray which is originating from a point situated a little above from the original point. The perceived point can be obtained by joining the bent light rays. The same is the case with all the points situated at the bottom. Thus, the swimming pool appears to be shallower than its actual depth. Therefore, the phenomenon of refraction is the reason for this apparent depth.
Hence, the correct answer is option A.

Note:
We have taken the position of the eye to be near to the normal to the surface of the pool. But that does not mean that this effect does not take place for the other position. In fact this effect is independent of the position of the eye, whether it is normally viewing, or obliquely viewing.