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NEET 2021 · Combination of Lenses

Combination of Lenses question from NEET 2021

Q44NEET 2021Medium

Combination of Lenses

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:

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Answer: (c)

Lens A focuses the parallel beam 20 cm behind it.
For B to give a parallel beam, this point must be at B's focus (5 cm behind B, virtual object).
$d = 20 - 5 = 15\text{ cm}$
So the answer is (c) 15.

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