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Haryana PMT Haryana PMT Solved Paper-2004

  • question_answer
    A concave mirror of focal length 15 cm forms an image having twice the linear dimension of the object. The position of the object when die image is virtual will be :

    A)  45 cm                                  

    B)  30 cm

    C)  7.5 cm                                 

    D)  22.5 cm

    Correct Answer: C

    Solution :

                                             Focal length of concave mirror \[f=-15cm\] magnification =2 (for virtual image) Linear magnification                                          \[m=\frac{size\,of\,image}{size\,of\,object}=-\frac{\upsilon }{u}\]                                          \[2=-\frac{\upsilon }{u}\] or \[\upsilon =-2u\] Now from the relation                                          \[\frac{1}{f}=\frac{1}{\upsilon }+\frac{1}{u}\] or                                    \[-\frac{1}{15}=\frac{1}{u}-\frac{1}{2u}=\frac{1}{2u}\] or                                    \[2u=-15\] or \[u=-7.5cm\]


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