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

Question

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

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

Monjur Alahi

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2025-01-04 04:42

1 Answers

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Salim Ahmed Kawsar · Accepted Answer · 2023-02-05T15:29:48+06:00

Salim Ahmed Kawsar

Correct Answer - 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`

4 views Answered 2023-02-05 15:29