Question

The filament of a lamp is 80 cm from a screen and a converging lens forms an image of it on a screen, magnified three times. Find the distance of the lens from the filament and the focal length of the lens.

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Answer 1

-u + v = 80 cm .......(1)

m = -3 (The image is real, since it forms on a screen)

Distance of lens from filament is 20cm.

v = -3u = 60 cm