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

Ab+BC+CA
30+60+60+40+40+30
260 answer

Answer 2

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

Explanation:

Given that,

Focal length of convex lens $f_{1}= 30 cm$

Focal length of concave lens $f_{2}= -60 cm$

The distance of the object u = -40 cm

The equivalent focal length is

$\dfrac{1}{f}=\dfrac{1}{f_{1}}+\dfrac{1}{f_{2}}$

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

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

$f = -60 cm$

Using the lens's formula

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

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

$v = -24 cm$

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