Verified Solution • 2025–26 Session moderate

QJEEM14Pha3f8: JEE Main 2014 Physics - Class 12 JEEM14Pha3f8 Solution: A thin convex lens made from crown glass has focal length .…

A thin convex lens made from crown glass (μ=32)\left( {\mu = {3 \over 2}} \right) has focal length ff . When it is measured in two different liquids having refractive indices 43{4 \over 3} and 53,{5 \over 3}, it has the focal lengths f1{f_1} and f2{f_2} respectively. The correct relation between the focal lengths is :

Multiple Choice Options

  • A f1=f2<f{f_1} = {f_2} < f
  • B f1>f{f_1} > f and f2{f_2} becomes negative
  • C f2>f{f_2} > f and f1{f_1} becomes negative
  • D f1 {f_1}\, and f2 {f_2}\, both become negative

Step-by-Step Verified Solution

By Lens maker's formula for convex lens

1f=(μμL−1)(2R){1 \over f} = \left( {{\mu \over {{\mu _L}}} - 1} \right)\left( {{2 \over R}} \right)

for, μL1=43,f1=4R\mu {L_1} = {4 \over 3},{f_1} = 4R

for μL2=53,f2=−5R\mu {L_2} = {5 \over 3},{f_2} = - 5R

⇒f2=(−)ve\Rightarrow {f_2} = \left( - \right)ve

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