Question

Why does the depth of water in a pond appear only three-fourths of its original depth? Explain with the help of a diagram.

Answer 1

1. 'Refraction of light' is responsible for this property.
2. When the light coming from a denser medium enters the rarer medium, it is bent away from the normal.
3. The pond appears to be three-quarters of its actual depth due to the property of refraction of light.

​​​​​​Refractive index, μ = Real depth / Apparent depth

Since μ= $\frac{4}{3}$ for water

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

Explanation of diagram -

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