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Physics · Geometrical Optics

JEE Main 2026 — 28 January, Morning Shift — Question 31

The magnitudes of power of a biconvex lens (refractive index 1.5) and that of a plano-concave lens (refractive index =1.7=1.7 ) are same. If the curvature of plano-concave lens exactly matches with the curvature of back surface of the biconvex lens, then ratio of radius of curvature of front and back surface of the biconvex lens is ____\_\_\_\_。

  1. Option A:

    5:25: 2

    Correct
  2. Option B:

    5:125: 12

  3. Option C:

    12:512: 5

  4. Option D:

    2:52: 5

Answer: A

Step-by-step solution

∣PA∣=∣PB∣\left|\mathrm{P}_{\mathrm{A}}\right|=\left|\mathrm{P}_{\mathrm{B}}\right| 0.5(1R1+1R2)=0.7R20.5\left(\frac{1}{\mathrm{R}_{1}}+\frac{1}{\mathrm{R}_{2}}\right)=\frac{0.7}{\mathrm{R}_{2}} 5R1=2R2\frac{5}{\mathrm{R}_{1}}=\frac{2}{\mathrm{R}_{2}} R1R2=52\frac{\mathrm{R}_{1}}{\mathrm{R}_{2}}=\frac{5}{2}

Solution figure

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Paper
28 January, Morning Shift
Subject
Physics
Chapter
Geometrical Optics
Topic
Lenses and Their Combinations, Silvering of Lens

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