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# Two point objects are placed on principal axis of a thin converging lens. One is 20 cm from the lens and other is on the other side of lens at a distance of 40 cm from the lens. The images of both objects coincide. The magnitude of focal length of lens is203cm403cm803cm40cm

A
803cm
B
203cm
C
403cm
D
40cm
Solution
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#### Let the two objects be Q1andQ2For Q11v−1u=1fNow, v=−v and u=−20Putting back the values, −1v+120=1fSimilarly, for O2,1v+140=1fSolving the 2 eqns simultaneously for f, we get f = 803

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