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NEET Sample Paper NEET Sample Test Paper-82

  • question_answer
    A concave mirror of focal length 20 cm produces an image twice the size of the object. If the image is real, then the distance of the object from the mirror is

    A)  10 cm             

    B)  30 cm

    C)  20 cm             

    D)  60 cm

    Correct Answer: B

    Solution :

    \[f\,\,-20cm,\,\,m=2\] As,                    \[m=\frac{-v}{-u}\] \[\therefore \,\,\,\,\,\,\,\,\,2=\frac{v}{u}\,\,\,\,\,\,\,or\,\,\,\,\,\,\,v=2\,u\] As,  \[\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\] \[\therefore \,\,\,\,\,\,\,\,\,\,\,\frac{1}{u}+\frac{1}{2\,u}=\frac{1}{-20}\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,u=-\,30\,cm\]


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