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BCECE Medical BCECE Medical Solved Papers-2008

  • question_answer
    A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of combination is

    A)  -1.5D        

    B)  -6.5D

    C)  + 6.5D        

    D)  4- 6.67 D

    Correct Answer: A

    Solution :

    Focal length of combination can be calculated as                 \[\frac{1}{f}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}\] \[\Rightarrow \] \[\frac{1}{F}=\frac{1}{40}+\frac{1}{(-25)}\] \[\Rightarrow \] \[\frac{1}{F}=\frac{-200}{3}cm\]                                 \[=\frac{100}{-200/3}\] = 1.5 D


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