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Lens problem with another medium of refractive index =2

  1. Oct 10, 2011 #1
    [SOLVED]
    I have got the answer.
    Answer is 40cm.

    ---------

    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.
     

    Attached Files:

    Last edited: Oct 10, 2011
  2. jcsd
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