A convex lens ‘A’ of focal length 20 cm and a concave lens ‘B’ of focal length 5 cm are kept along the same axis with a distance ‘d’ between them. If a parallel beam of light falling on ‘A’ leaves ‘B’ as a parallel beam, then the distance ‘d’ in cm will be:
medium
Ray Optics and Optical Instruments
2021
physics
25
15
50
30
Explanation
To solve this problem, we need to understand the behavior of light passing through a lens system.The condition given is that a parallel beam of light falling on lens 'A' leaves lens 'B' as a parallel beam.This implies that the system of lenses is acting as a telescope in normal adjustment, where the image formed by the first lens (convex lens 'A') is at the focal point of the second lens (concave lens 'B').Let's denote:• fA​=20
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