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CMC Medical CMC-Medical VELLORE Solved Paper-2008

  • question_answer
    A concave lens of focal length 20 cm produces an image half the size of the real object. The distance of the real object is

    A)  20 cm                                  

    B)  30 cm

    C)  10 cm                                  

    D)  60 cm

    E)  40 cm

    Correct Answer: A

    Solution :

                    From lens formula \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] Giveh, \[v=\frac{u}{2},\]\[f=20\,cm\] \[\Rightarrow \]               \[\frac{1}{20}=\frac{1}{u\text{/}2}-\frac{1}{u}=\frac{1}{u}\] \[\Rightarrow \]                  \[u=20\,cm\]


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