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Q 9.19  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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As we know for real image, the maximum focal length is given by 

f_{max}= \frac{d}{4}   

where d is the distance between the object and the lens.

So putting values we get,

f_{max}= \frac{3}{4}=0.75

Hence maximum focal length required is 0.75.

Posted by

Pankaj Sanodiya

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