A thin plano-convex lens is placed on a plane mirror as shown in the figure. The radius of curvature of curved surface is 40 cm. the refractive index of material of lens `n_(1)=1.5`. The refractive index surrounding is `n_(0)=1.2` An object O starts moving parallel to plane mirror. if final image of object moves with same speed as that of the object initially then distance of object O from the plane mirror is.

Options

A. 80 cm
B. 120 cm
C. 160 cm
D. none of these

Answer

C

Explanation

Since `m=-1` so distance of object from mirror should be `2f_(eq)`
`(-1)/(f_(eq))=((n)/(n_(0))-1)(2)/(R)`
`f_(eq)=80cm`