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NEET AIPMT SOLVED PAPER MAINS 2011

  • question_answer
    A conversing beam of rays is incident on a diverging lens. Having passed through the lens the rays intersect at a point 15 cm from the lens on the opposite side. If the lens is removed the point where the rays meets will move 5 cm closer to the lens. The focal length of the lens is                            

    A)  -10 cm                 

    B)  20 cm  

    C)  -30 cm                 

    D)  5 cm

    Correct Answer: C

    Solution :

    Given \[u=10\,cm,\,v=15\,cm\] \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] \[\frac{1}{f}=\frac{1}{15}-\frac{1}{10}\] \[\frac{1}{f}=\frac{10-15}{150}\] \[\frac{1}{f}=\frac{-5}{150}\] \[f=-30\,cm\]


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