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A concave lens has focal length of 25 cm. At what distance should the object from the lens be placed so that if it forms an image at 20 cm distance from the lens? Also find the magnification produced by the lens.
Asked by Topperlearning User | 04 Jun, 2014, 01:23: PM
answered-by-expert Expert Answer

A concave lens always forms a virtual, erect image on the same side of the object.

v = -20 cm, f = -25 cm, u =?

1/v -1/u = 1/f

1/u = 1/(-20) - 1/(-25)

1/u = -1/100

u = -100cm

Thus, object distance is 100 cm.

Magnification= v/u = -20/ (-100) = + 0.5

Thus, image is erect, virtual and is half of the size of object.

Answered by | 04 Jun, 2014, 03:23: PM

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