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Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2007

  • question_answer
    Radius of curvature of concave mirror is 40 cm and the size of image is twice as that of object, then the object distance is

    A)  60 cm                                  

    B)  20 cm

    C)  40cm                                   

    D)  30cm

    Correct Answer: D

    Solution :

    Given, \[R=2f=40\text{ }cm.\] \[\therefore \]  \[f=20cm\]                 \[m=2\]                 \[m=\frac{v}{u}=2\] \[\therefore \]  \[v=2u\] Using mirror formula,                 \[\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\]                 \[\frac{1}{20}=\frac{1}{2u}+\frac{1}{u}=\frac{1+2}{2u}\]                 \[u=30cm\]


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