Question

A parallel beam of light is incident on diverging lens of focal length 12cm. The emergent beam passes through a converging lens of focal length 20cm placed coaxial with it. The beam which finally emerges from the converging lens,comes out parallel. What is the separation of the lenses? Illustrate your answer with a diagram.

Answer 1

12 cm + (lens separation)= 20 cm
lens separation = 8 cm

We don't do illustrations.

The rays leaving the diverging lens expand from a point 12 cm in front of that lens. That same point is the focal point of the converging lens, 20 cm in front of it.