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A plano convex lens has focal length f =...

A plano convex lens has focal length `f = 20 cm`. If its plano surface is silvered, then new focal length will be.

A

20 cm

B

40 cm

C

30 cm

D

10 cm

Text Solution

Verified by Experts

The correct Answer is:
D
(d) The focal length of the plano-convex lens is 20 cm with the plane surface bieng silvered.
So, the net power of the lens is given by
`P=1/fxx2=2/f`
Thus, the net focal length is, `f/2=20/2=10 cm`
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