Question

A 3 cm tall bulb is placed at a distance of 20 cm from a diverging lens having a focal length of 10.5 cm. Determine the distance of the image.

Answer 1

Given: 3 cm tall bulb is placed at a distance of 20 cm from diverging lens having focal length of 10.5 cm

To find the distance of the image

Solution:

According to the given criteria,

Height of object, $h=3cm$

Object distance from lens, $u=-20cm$

Focal length of the lens, $f=-10.5cm$ (as diverging lens)

Applying lens formula,

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}⟹\frac{1}{-10.5}=\frac{1}{v}-\frac{1}{-20}⟹\frac{1}{v}=\frac{1}{-10.5}-\frac{1}{20}⟹\frac{1}{v}=\frac{-20-10.5}{10.5\times 20}⟹\frac{1}{v}=\frac{-30.5}{210}⟹v=-6.88cm$

is the distance of image from the lens on the same side of the lens.