Question

A convex lens of focal length 30 cm and concave lens of focal length 60 cm are placed in combination. If the object is placed 40 cm away from the combination. Find the position of the image.

Answer 1

Answer:

The image is formed 24 cm from the lens and image is virtual.

Explanation:

Given that

Focal length of convex lens $f_1 = 30cm$

Focal length of concave lens $f_2 = 60cm$

The distance of the object u = -40 cm

The equivalent focal length is

$\frac{1}f = \frac{1}{f_1} + \frac{1}{f_2}$

$\frac{1}f = \frac{1}{30} - \frac{1}{60}$

$\frac{1}f = \frac{-30}{1800}$

f = -60cm

Using the lens's formula

$\frac{1}f = \frac{1}v - \frac{1}u$

$\frac{1}{-60} = \frac{1}v - \frac{1}{-40}$

v = -24cm

Hence, The image is formed 24 cm from the lens and image is virtual.