"A thin lens made of glass (refractive index = 1.5) of focal length f = 16 cm is immersed in a liquid of refractive index 1.42. If its focal length in liquid is f1 , then the ratio ${{{f_1}} \over f}$ is closest to the integer :"

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"Using formula
$${1 \over f} = \left( {{{{\mu _2}} \over {{\mu _1}}} - 1} \right)\left( {{1 \over {{R_1}}} - {1 \over {{R_2}}}} \right)$$

$${1 \over {{f}}} = \left( {{{1.5} \over 1} - 1} \right)\left( {{1 \over {{R_1}}} - {1 \over {{R_2}}}} \right)$$ ...(1)

and $${1 \over {{f_1}}} = \left( {{{1.5} \over {1.42}} - 1} \right)\left( {{1 \over {{R_1}}} - {1 \over {{R_2}}}} \right)$$ ...(2)

Dividing (1) by (2), we get

${{{f_1}} \over f} = {{0.5} \over {0.056}}$ = 8.93 $\approx$ 9 "

A thin lens made of glass (refractive index = 1.5) of focal length f = 16 cm is immersed in a liquid of refractive index 1.42. If its focal length in liquid is f₁ , then the ratio ${{{f_1}} \over f}$ is closest to the integer :

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A thin lens made of glass (refractive index = 1.5) of focal length f = 16 cm is immersed in a liquid of refractive index 1.42. If its focal length in liquid is f1 , then the ratio ${{{f_1}} \over f}$ is closest to the integer :

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A thin lens made of glass (refractive index = 1.5) of focal length f = 16 cm is immersed in a liquid of refractive index 1.42. If its focal length in liquid is f₁ , then the ratio ${{{f_1}} \over f}$ is closest to the integer :