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CMC Medical CMC-Medical Ludhiana Solved Paper-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 the combination in dioptre is

    A)  - 1.5                                     

    B)  - 6.5

    C)  + 6.5                                    

    D)  + 6.67

    Correct Answer: A

    Solution :

                    \[\frac{1}{f}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}\] \[\frac{1}{f}=\frac{1}{40}+\frac{1}{-\,25}\] \[\Rightarrow \]               \[f=\frac{-\,40\times 25}{40-25}\] \[\Rightarrow \]               \[f=-\,66.67\,cm\] \[\therefore \]  \[P=\frac{1}{f(in\,m)}=-\frac{100}{66.67}=-1.5\,D\]


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