Question

Water in a pond appears to be only three-quarter of its actual depth. (a) What property of light is responsible for this observation? Illustrate your answer with the help of a ray diagram. (b) How the refractive index of water calculated from its real and apparent depths?

Answer 1

(a) 'Refraction of light' is responsible for this property.

(b) When light coming from denser medium enters the rarer medium, it is bent away from the normal.

Let any object B is at the bottom of a pond. Consider a light ray BC from the object that moves from water to air. After refraction from the water surface, the ray moves away from the normal N along the path CD. The produce of CD appears from the point B' and a virtual image of the object at B appears at B'.

(c) The pond appears to be three-quarters of its actual depth due to the property of refraction of light.

​​​​​​Refractive index $\mu =\frac{\text{Real depth}}{\text{Apparent depth}}$

Since $\mu =\frac{4}{3}$ for water

Therefore, Apparent depth = $\frac{4}{3}\times$ Real depth