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I have got the answer.

Answer is 40cm.

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1. The problem statement, all variables and given/known data

Focal length of thin lens in air is 10 cm.now medium of one side of lens is replaced by medium of refractive index μ=2.the radius of curvature of lens with contact with the medium is 20cm. Find the new focal length.

let refractive index of lens=μ

radius of curvature of left surface (R1) of lens is not given

refer attachment

3. The attempt at a solution

assuming parallel rays so u=[itex]\infty[/itex]

applying refraction formula at first surface

[itex]μ/v1-1/\infty=μ-1/R1[/itex]

similarly

applying refraction formula at second surface

[itex]2/v-μ/v1=2-μ/-20[/itex]

adding both

[itex]\frac{μ}{v1}-\frac{1}{\infty}+\frac{2}{v}-\frac{μ}{v1}=\frac{μ-1}{R1}+\frac{2-μ}{-20}[/itex]

[itex]\frac{2}{v}=\frac{μ-1}{R1}+\frac{2-μ}{-20}[/itex]

After that I am unable to solve

Any help will be highly appreciated.

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# Homework Help: Lens problem with another medium of refractive index =2

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