A thin plano-convex lens acts like a concave mirror of radius of curvature `20 cm` when its plane surface is silvered. The radius of curvature of the curved surface if index of refraction of its matarial is `1.5` will be

Options

A. 40 cm
B. 30 cm
C. 10 cm
D. 20 cm

Answer

C

Explanation

(c ) We have, `1/f=(2mu)/(R_(2))-(2(mu-1))/(R_(1))`
`1/(-10)=(2xx1.5)/(oo)-(2(1.5-1))/(R )`
`therefore` R=10 cm