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AMU Medical AMU Solved Paper-2002

  • question_answer
    A convex lens of focal length 20 cm produces a real image twice the size of the object. Then the distance of the object from the lens is

    A)  10 cm                                  

    B)  20 cm

    C)  30 cm                                  

    D)  60 cm

    Correct Answer: C

    Solution :

                     From lens formula                 \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\]                      ... (i) Also magnification \[(m)=\frac{v}{u}\]   ... (ii) Given,   \[f=20\,cm\],     \[v=2\,\,u\] \[\therefore \] From Eqs. (i) and (ii), we get                 \[\frac{1}{20}=\frac{1}{2\,u}-\frac{1}{-u}\] \[\Rightarrow \]               \[\frac{1}{20}=\frac{1}{2\,u}+\frac{1}{u}\]


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