Question

One end of a cylindrical glass rod $(\mu =1.5)$ in given in the shape of a concave refracting surface of radius 10 cm. an air bubble is situated in the glass rod at a point on its axis such that it appears to be at a distance 10 cm from the surface inside the glass when seen from the other medium. find the actual location of air bubble from the surface:

• A. 10 cm inside the glass
• B. 20 cm outside the glass
• C. 30 cm inside the glass
• D. 40 cm outside the glass

Answer 1

The correct option is C 30 cm inside the glass

Using the lens maker's formula

$\frac{{\mu }_2}{v}-\frac{{\mu }_1}{u}=\frac{{\mu }_2-{\mu }_1}{R}$

Substituting the values:

$\frac{-1}{10}+\frac{1.5}{u}=\frac{1-1.5}{10}$

This gives on solving, $u=30cm$

30 cm inside the glass.

Hence option C is correct.