Punjab Medical Punjab - MET Solved Paper-2007

  • question_answer
    An object is placed at a distance of\[\frac{f}{2}\]from a convex lens. The image will be

    A)  at one of the foci, virtual and double its size

    B)  at\[\frac{3f}{2}\], real and inverted

    C)  at\[2f\], virtual and erect

    D)  none of the above

    Correct Answer: A

    Solution :

    From lens formula                 \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\]      (Given\[u=-\frac{f}{2}\]) \[\Rightarrow \]               \[\frac{1}{f}=\frac{1}{v}+\left( \frac{1}{f/2} \right)\] \[\Rightarrow \]               \[\frac{1}{v}=\frac{1}{f}-\frac{2}{f}\] \[\Rightarrow \]               \[\frac{1}{v}=-\frac{1}{f}\]and\[m=\frac{v}{u}=\frac{f}{f/2}=2\] So, virtual at the focus and of double size.


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