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AMU Medical AMU Solved Paper-2007

  • 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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