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 large convex lens. What is the maximum possible focal length of the lens required for the purpose ?
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For a real image (on wall), minimum distance between the object and image should be `4 f`. `:. 4f = 3m :. F = (3)/(4)m = 0.75m`
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