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JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2010

  • question_answer
        Two plano-convex lenses of radius of curvature R and refractive index\[\mu =1.5\]will have equivalent focal length equal to R when they are placed

    A)  at distance R/4

    B)  at distance R/2

    C)  at distanced

    D)  in contact with each other

    Correct Answer: C

    Solution :

                    For plano-convex lens \[\frac{1}{f}=\frac{(\mu -1)}{R}\] \[=\frac{1.5-1}{R}=\frac{1}{2R}\] When placed in contact                 \[\frac{1}{F}=\frac{1}{f}+\frac{1}{f}=\frac{1}{2R}+\frac{1}{2R}=\frac{1}{R}\] \[\therefore \]  \[f=R\]


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