A concave lens of focal length 20 cm pla...

A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a

convex mirror of focal length 10 cm

concave mirror of focal length 40 cm

concave mirror of focal length 60 cm

concave mirror of focal length 10 cm

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Verified by Experts

The correct Answer is:

(a) Power, `P=2P_(L)+P_(M)`
or `-1/F=2(-1/0.2)+0orF= 10cm`
On silvering the surface of the lens, it behaves as a mirror.
Therefore, the combination behaves as a convex mirror of focal length 10 cm.

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