1.

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 ?

Answer»

SOLUTION :For fixed DISTANCE ‘s’ between object and screen, for the LENS equation to give real solution for u = v = 2f, ‘f’ should not be GREATER than4f = s.
`THEREFORE f=s//4`


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