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CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2000

  • question_answer
    An object is placed at a distance of 30 cm from a concave mirror and its real image is formed at a distance of 30 cm from the mirror. The focal length of the mirror is:

    A)  60 cm                                  

    B)  45 cm  

    C)         30cm                   

    D)         20cm

    E)  15cm

    Correct Answer: E

    Solution :

    From the lens formula \[\frac{1}{f}=-\left( \frac{1}{v}+\frac{1}{u} \right)=-\left( \frac{1}{30}+\frac{1}{30} \right)=-\frac{2}{20}=-\frac{1}{15}\] \[\Rightarrow \]               \[f=15\,cm\]


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