JEE Main 2019PhysicsRay OpticsMediumMCQ

JEE Main 2019 — Ray Optics Question with Solution

JEE Main 2019 (10 Apr Shift 1)

Question

One plano-convex and one plano-concave lens of the same radius of curvature R but of different materials are joined side by side as shown in the figure. If the refractive index of the material of 1 is μ1 and that of 2 is μ2, then the focal length of the combination is:

Choose an option

Show full solutionCorrect option: D
Correct answer
DRμ1-μ2

Step-by-step explanation

From lens maker’s formula,
1f=μ-11R1-1R2
1f1=μ1-11∞-1-R=μ1-1R
1f2=μ2-11-R-1∞=-μ2-1R
1feq=1f1+1f2=μ1-1R-μ2-1R
=μ1-μ2R
feq=Rμ1-μ2

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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.