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NEET AIPMT SOLVED PAPER 2002

  • question_answer
                    A body is located on a wall. Its image of equal size is to be obtained on a parallel wall with the help of a convex lens. The lens is placed at a distance d ahead of second wall, then the required focal length will be:

    A)                                                                                                                                                                                            only \[\frac{d}{4}\]                                                         

    B)                 only \[\frac{d}{2}\]         

    C)                 more than \[\frac{d}{4}\] but less than \[\frac{d}{2}\]   

    D)                 less than \[\frac{d}{4}\]

    Correct Answer: B

    Solution :

                              The lens formula can be written as                 \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}....(i)\]                 Given,  v = d                 For equal size image                 |v| = |u| = d                 By sign convention, u = -d                 \[\therefore \frac{1}{f}=\frac{1}{d}+\frac{1}{d}\]                 \[orf=\frac{d}{2}\]


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