Question

An object is placed at a distance of 5 cm more than the focal length f of a convex lens. Its real image is formed at a distance 3 f beyond the focus. The focal length f of the lens is?
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Answer 1

Explanation:

Let magnitude of focal length of convex lens=x

Then u=−(x−5) and v=3x

as v1−u1=f1or3x1−−(x−5)1=x1orx+51=3x2or3x=2x+10∴x=10cm

Hence f=+10cm

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Answer 2

Answer:

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