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RAJASTHAN PMT Rajasthan - PMT Solved Paper-2003

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

    A)  -6.5D                                   

    B)  +6.5D

    C)  -1.5D                   

    D)         +1.5D

    Correct Answer: C

    Solution :

    Power of convex lens \[{{P}_{1}}=\frac{1}{f(metre)}D\] \[=\frac{1}{0.40}-+2.5D\] Power of concave lens                                 \[{{P}_{2}}=\frac{1}{(-0.25)}D=-4D\] \[\therefore \]Power of combination (in contact) \[P={{P}_{1}}+{{P}_{2}}\]     \[=+2.5D-4D=-1.5D\]


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