Mon March 12, 2012 By:

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.

Expert Reply
Tue March 13, 2012
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
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