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

A plano convex lens has focal length `f = 20 cm`. If its plane 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
`(1)/(f_(eq)) = (2)/(f_(lens)) + (1)/(f_(mirror))`
`rArr (1)/(f_(eq)) = (2)/(20) + (1)/(infty) rArr f_(eq) = 10` cm.
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