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JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        A luminous object is placed 20 cm from surface of a convex mirror and a plane mirror is set, so that virtual mirror is at a distance of 12 cm from object, then focal length of convex mirror is

    A)  5 cm                                     

    B)  10 cm

    C)  20cm                                   

    D)  40cm

    Correct Answer: A

    Solution :

                    Here, \[u=-20cm,\text{ }v=12+12-20=4cm\] \[\therefore \]  \[\frac{1}{f}=\frac{1}{v}+\frac{1}{u}=\frac{1}{4}-\frac{1}{20}\]                 \[=\frac{5-1}{20}\]                 \[=\frac{4}{20}=\frac{1}{5}\] \[\therefore \]  \[f=5\,cm\]


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