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Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2011

  • question_answer
    An object placed 10 cm in front of lens has an image 20 cm behind the lens. What is the power of the lens (in diopter)?

    A)  1.5 D                                    

    B)  3.0 D

    C)  -15 D                                    

    D)  +15D

    Correct Answer: D

    Solution :

    Given, \[u=-10\text{ }cm\]and \[v=20\text{ }cm\] \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\]                 \[\Rightarrow \]               \[\frac{1}{f}=\frac{1}{20}+\frac{1}{10}\]                                 \[f=\frac{20}{3}\]                 Power   \[P=\frac{100}{f}=\frac{100\times 3}{20}=+15D\]


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