Verified Solution • 2025–26 Session moderate

QJEEM20Ph223d: JEE Main 2020 Physics - Class 12 JEEM20Ph223d Solution: A double convex lens has power P and same radii of curvature R…

A double convex lens has power P and same radii of curvature R of both the surfaces. The radius of curvature of a surface of a plano-convex lens made of the same material with power 1.5 P is :

Multiple Choice Options

  • A R3{R \over 3}
  • B 3R2{{3R} \over 2}
  • C R2{R \over 2}
  • D 2R

Step-by-Step Verified Solution

Assume refractive index = μ\mu ll

P = (μl−1)(2R)\left( {{\mu _l} - 1} \right)\left( {{2 \over R}} \right) .....(1)

32P=(μl−1)(1R1){3 \over 2}P = \left( {{\mu _l} - 1} \right)\left( {{1 \over {{R_1}}}} \right) ......(2)

from (1)/(2)

P32P=(2R)(1R1){P \over {{3 \over 2}P}} = {{\left( {{2 \over R}} \right)} \over {\left( {{1 \over {{R_1}}}} \right)}}

⇒\Rightarrow R1 = R3{R \over 3}

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