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The image of a small electric bulb fixed...

The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3m 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 fixed distance s between object and screen, the lens equation does not give a real solution for u or v if f is greater than s/4. Therefore, fmax = 0.75 m.
Therefore, `f_("max")=0.75m`.
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An object is there on a wall. Now by help of convex lens, an image of object is obtained of same size as of object on the opposite parallel wall. If the lens is at distance d from second wall, then what should be the focal length of lens ?

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NCERT GUJARATI-RAY OPTICS AND OPTICAL INSTRUMENTS-EXERCISES
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