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Question
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.

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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# in an experiment the focal length of a convex lens a student obtained a sharp and inverted image of a distant tree on the screen behind the lens.she then removed the screen and looked through lens in the direction of the object .she will see a) an inverted image of the tree at the focus of the lens b)no image as the screen is removed c) a blurered image on the wall of laboratory d0 an erect image of the tree on the lens pls explain me the answer elaborately

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