Question

A ball of negligible dimensions is drowned till an apparent measured depth of 15 m in a lake. What is the depth of the lake?

• A. 30
• B. 20
• C. 50
• D. 60

Answer 1

The correct option is B 20

The real depth (d) of the lake is related to is apparent depth by :

$\frac{d}{d^{\prime }}=\mu [\mu :\text{Refractive index for water}=\frac{4}{3}]$

$\Rightarrow d=d^{\prime }\mu \Rightarrow d=15\times \frac{4}{3}=20m.$

$\therefore$ Real depth of lake $=20m$.