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10th Class Science Light - Reflection and Refraction Question Bank Light

  • question_answer
    A virtual image twice as big as the object is formed by a concaved lens when the object is 10 cm away from it. A real image twice as big as the object will be formed when it is placed at a distance from the lens

    A)  40 cm                  

    B)         30 cm  

    C)  20cm                   

    D)         15cm

    Correct Answer: B

    Solution :

     From the formula,          \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] we have,             \[u=\frac{f(m-1)}{m}\] For virtual image, \[m=+2,\] and for real image, \[m=-2\] \[\therefore \]  \[-10=-\frac{f(2-1)}{2}\] (Real object distances are always negative.) \[\Rightarrow \]               \[f=20\] For the real image,\[u=\frac{f(-2-1)}{-2}=\frac{-20(-1)}{-2}=30\]


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