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WB JEE Medical WB JEE Medical Solved Paper-2011

  • question_answer
    A convex lens of focal length 30 cm produces 5 times magnified real image of an object. What is the object distance?

    A)  36 cm                                  

    B)  25 cm

    C)  30 cm                                  

    D)  150 cm

    Correct Answer: A

    Solution :

                     We have a lens of focal, length 30 cm that produces 5 times magnified real image. So, we have \[\frac{1}{5u}-\left( \frac{1}{-u} \right)=\frac{1}{30}\]                 Hence,                  \[\frac{1}{5u}+\frac{1}{u}=\frac{5+1}{5u}\]                                                 \[=\frac{1}{30}\]                 So,                          \[u=36\,cm\]


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