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JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        A combination of convex and concave lenses has power 4D. If the convex lens has power 5D the focal length of the concave lens will be

    A)  100 cm                                

    B)  \[-100cm\]

    C)  \[-1\,cm\]                         

    D)  \[-\frac{100}{9}\,cm\]

    Correct Answer: B

    Solution :

                    Power of combination \[P={{P}_{1}}+{{P}_{2}}\] \[\Rightarrow \]               \[4+5+{{P}_{2}};{{P}_{2}}=4-5=-1\,D\] \[\therefore \]  \[-1={{P}_{2}}=\frac{100}{f(cm)}\Rightarrow f=-100\,cm\]


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