JEE Main 2019PhysicsRay OpticsHardMCQ

JEE Main 2019 — Ray Optics Question with Solution

JEE Main 2019 (12 Jan Shift 2)

Question

A plano - convex lens (focal length f2 , refractive index μ2, radius of curvature R) fits exactly into a plano - concave lens (focal length f1, refractive index μ1, radius of curvature R). Their plane surfaces are parallel to each other. Then, the focal length of the combination will be:

Choose an option

Show full solutionCorrect option: A
Correct answer
ARμ2 - μ1

Step-by-step explanation

1f1=μ1-11-R-1ω 1f2=μ2-11R-1ω

When joined together

1feq=1f1+1f2=μ2-1-R+μ2-1R=μ2-μ1R

⇒feq=Rμ2-μ1

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About this question

This is a previous-year question from JEE Main 2019, 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.