Question

Consider the situation shown in figure, water $({\mu }_w=4/3)$ is filled in a beaker up to a height of $10\text{cm}$. A plane mirror fixed at a height of $5\text{cm}$ from the surface of water. Distance of image from the mirror after reflection from it of an object $O$ at the bottom of the beaker is

• A. $15\text{cm}$
• B. $12.5\text{cm}$
• C. $7.5\text{cm}$
• D. $10\text{cm}$

Answer 1

The correct option is B $12.5\text{cm}$

Here,
${\mu }_1=1,{\mu }_2=4/3,d_1=10\text{cm}$

Apparent depth will be given as

$d_2=\frac{d_1}{{\mu }_{relative}}$

$\therefore d_2=\frac{10}{(\frac{4/3}{1})}=\frac{30}{4}=7.5\text{cm}$

So effective object distance will be,

$u=(7.5+5)=12.5\text{cm}$

So the image will be formed at $12.5\text{cm}$ behind the plane mirror.

Hence, option $\left(b\right)$ is correct.