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A beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12cm from P. At what point does the beam converge if the lens is (a) a convex lens of focal length 20cm, and (b) a concave lens of focal length 16cm? |
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Answer» Here , the POINT P on the RIGHT of the lens acts as a virtual object u=12 CM , v=? (a) f=20cm As 1/f =1/v -1/u 1/v -1/12= 1/20 1/v =1/20 +1/12= 8/60 v=60/8= 7.5cm IMAGE is at 7.5 cm to the right of the lens where the BEAM converges. (b) f= -16cm , u=12 cm As, 1/f =1/v -1/u 1/v= 1/f +1/u = -1/16 +1/12 = 1/48 v= 48cm Hence image is at 48cm to the right of the lens, where the beam would converge.Hope this helps! |
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