While finding out the focal length of a convex lens,Ashok kept it on a stand on the optical bench at 10.5 cm. He adjusted the stand carrying the screen to obtain sharp image of a distant tree on it and finally got it when this stand was at 20.8 cm on the optical bench.Find the focal length of the lens.

Asked by  | 12th Mar, 2012, 09:07: PM

Expert Answer:

so the image distance=20.8-10.5=10.3 cm.
object distance=infinity as the obj is far away.
so???? putting in the lens formula:we get:1/f =1/10.3
so  f= 10.3 cm

Answered by  | 13th Mar, 2012, 01:27: PM

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