NEET Sample Paper NEET Sample Test Paper-16

  • question_answer 20) The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3 m away by means of a convex lens. What is the maximum focal length of the lens for this purpose?

    A) 0.5 m             

    B) 0.75 m

    C)      1.0 m             

    D)      1.5 m              

    Correct Answer: B

    Solution :

    To obtain a real image on a screen, the minimum distance \[({{X}_{\min }})\] between the object and the screen is 4f, where f is the focal length of the lens. Conversely, for a fixed distance between the object and the screen, the convex lens should have a maximum focal length of \[{{f}_{\max }}=\frac{{{X}_{\min }}}{4}=\frac{3}{4}=0.75\,m.\] Hence, the correction option is (b).

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