Question

An object is placed at 15cm from a lens.Its double size erect image is formed.Is the lens convex of concave? Find the focal length of the lens.​

Answer 1

Explanation:

Here point I would be center of curvature of the mirror.

So focal length of mirror f=2MI

For lens, f1=v1−u1

v1=f1+u1

Here , f=+10cm,u=−15cm

v1=101+−151

v=+30cm

MI=LI−LM

=30−10=20cm

f=2MI=220

f=10cm

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