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

Options

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

Answer

D

Explanation

The focal length of convex side of the plano convex lens is 0.4 because after entering the plane surface, it will behave like a concave mirror of focal length =`(f_(1)ems)/(2)`
  As ftirror = 0.2 m, fiere = 0.4 m, From lens maker.s formula
`(1)/(f)=(mu-1)[(1)/(R_(C))-(1)/(R_(p))]`
`rArr`    `(1)/(0.4)=0.5(1)/(R_(C))rArrR_(C)=0.2m`