Question

A point object $O$ is placed in front of a glass rod having spherical end of radius of curvature $30cm$. The image would be formed at

• A. 30 cm left
• B. infinity
• C. 1 cm to the right
• D. 18 cm to the left

Answer 1

Answer: (A)

Focal length of glass rod, $f=\frac{R}{2}=\frac{30}{2}=15cm$
Distance of object, $u=-15cm$
From formula
$\frac{{\mu }_2}{v}-\frac{{\mu }_1}{u}=\frac{{\mu }_2-{\mu }_1}{R}$
${\mu }_2=1.5$ (for glass)
${\mu }_1=1$ (for air)
$\frac{1.3}{v}-\frac{1}{-15}=\frac{1.5-1}{30}$
$v=-30cm$