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

• A. 0.4 m
• B. 0.2 m
• C. 0.1 m
• D. 0.75 m

Answer 1

Answer: (B)

0.2 m

Answer 2

f = $\frac { \mathrm { R } } { 2 ( \mu - 1 ) }$ Ž R = 2f (µ – 1) = 2 × 0.2(1.51–1)

R = 0.2 m