Question

A lens forms an image at 40 cm from it when the object is at 20 cm from it. What is the ratio between the image and object size?
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Answer 1

Answer:

Correct option is C)

Image of a distant object is formed at the focus.

The image due to first lens is formed at 20 cm. Hence, f

1

=20cm

The image due to combined lens is formed at 40/3 cm. Hence, f

eq

=

3

40

f

eq

=

f

1

+f

2

f

1

f

2

⇒f

eq

=

20+f

1

20×f

1

=

3

40

3f

1

=40+2f

1

f

1

=40cm