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RAJASTHAN PMT Rajasthan - PMT Solved Paper-2005

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


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