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NEET Sample Paper NEET Sample Test Paper-23

  • question_answer
    The magnification of an object placed in front of a convex lens of focal length 20 cm is +2. To obtain a magnification of -2, the object has to be moved a distance equal to

    A)  10 cm            

    B)  20 cm

    C)  30 cm            

    D)  40 cm

    Correct Answer: B

    Solution :

    When magnification is \[+2,u=x,v=-2x,f=20\]Using \[\frac{1}{v}+\frac{1}{u}=\frac{1}{f},-\frac{1}{2x}+\frac{1}{x}=\frac{1}{20}\]or \[x=10\,cm\]To have a magnification of \[-2,u=y,v=2y,f=20\] \[\therefore \]\[\frac{1}{2y}+\frac{1}{y}=\frac{1}{20}\]or \[y=30\,cm\] \[\therefore \]\[y-x=20\,cm.\] Hence, the correction option is [b].


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