Question

a convex lens forms a real image on a screen when object is placed at 10 cm from the screen. on shifting the lens by 2cm, a real image is again formed on the screen. find the focal length
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Answer 1

Explanation:

this is formula of finding focal length using displacement method.

f:− focal length

Δ:− displacement of lens done in order to get image again on screen.

D:−  distance between object and screen  

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 f=10²-2² /4×10

f=2.4 cm