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CET Karnataka Medical CET - Karnataka Medical Solved Paper-2014

  • question_answer
    An object is placed at 20 cm in front of a concave mirror produces three times magnified real image. What is focal length of the concave mirror?

    A)  \[10cm\]        

    B)  \[15cm\]

    C)  \[7.5cm\]        

    D)  \[6.6cm\]

    Correct Answer: B

    Solution :

    : As image is real \[\therefore \] Magnification, \[m=-\frac{v}{u}=-3\]or \[v=3u\] Here, \[u=-20\text{ }cm\] \[\therefore \]  \[v=-60cm\] According to mirror formula \[\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\] \[\frac{1}{f}=\frac{1}{-60}+\frac{1}{-20}=-\frac{4}{60}\] \[f=-15cm\] \[|f|=15cm\]


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