CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    The radius of curvature of the convex face of a planoconvex lens is 15 cm and the refractive index of the material is 1.4. Then the power of the lens in dioptre is

    A)  1.6                        

    B)         1.66      

    C)  2.6        

    D)         2.66

    E)  1.4

    Correct Answer: D

    Solution :

    \[\frac{1}{f}(\mu -1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] For planoconvex lens \[{{R}_{1}}=\infty ,{{R}_{2}}=-R=-1.5\,cm,\mu =1.4\] \[\therefore \]\[\frac{1}{f}=(1.4-1)\left( 0+\frac{1}{15} \right)\]or\[\frac{1}{f}=0.4\times \frac{1}{15}\] Therefore, power of the lens in diopter \[P=\frac{100}{f}=\frac{40}{15}=2.66D\]


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