JEE Main 2022PhysicsRay OpticsHardNumerical

JEE Main 2022 — Ray Optics Question with Solution

JEE Main 2022 (24 Jun Shift 1)

Question

Two identical thin biconvex lenses of focal length 15 cm and refractive index 1.5 are in contact with each other. The space between the lenses is filled with a liquid of refractive index 1.25. The focal length of the combination is _____ cm.

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Show full solutionCorrect answer: 10
Correct answer
10

Step-by-step explanation

For convex lenses, let radius of curvature is R. Then,

115 cm=1.5-11R-1-R

⇒1R=115 ⇒R=15 cm

Now for concave lens,

1fconcave=1.25-11-R-1R

=14×-2R=-130

1feff=115+115-130=-110

⇒feff=-10 cm

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About this question

This is a previous-year question from JEE Main 2022, covering the Ray Optics chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.