InterviewSolution
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                                    Wheh the object is at distances x1 and x2 from the thin lens, theh the object is at distances x and 2 from the thin lens, the two images formed areof same size but the one is real and the other is virtual, respectively. The focal length cofthe lens is | 
                            
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Answer»  Let us say it is a convex lens of focal length f. It can form both real and virtual images. 1/v1 - 1/x= 1/f, here v & f are positive and u is negative.1/v1 + 1/x1 = 1/f --- (1)=> x1/v1 + 1 = x1/f -- (2) The virtual image is formed in front of the lens. So v and u1 are negative.- 1/v2 + 1/x2 = 1/f --- (3)- x2/v2 + 1 = x2/f --(4) Magnification = v1/x1 = v2/x2 ---(5) Add (2) and (4) and use (5) to get: 2 = x1/f + x2/f => f = (x1 + x2)/2  | 
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