Optics Question 679

Question: A thin plano-convex lens acts like a concave mirror of focal length 0.2 m when silvered from its plane surface. The refractive index of the material of the lens is 1.5. The radius of curvature of the convex surface of the lens will be

[KCET 2004]

Options:

A) 0.4 m

B) 0.2 m

C) 0.1 m

D) 0.75 m

Show Answer

Answer:

Correct Answer: B

Solution:

$ f=\frac{R}{2(\mu -1)} $

$ \Rightarrow R=2f(\mu -1) $

$ =2\times 0.2(1.5-1) $ =0.2m.



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