An object, a convex lens of focal length `20 cm` and a plane mirror are arranged as shown in the figure. How far behind the mirror is the second image formed?

Options

A. `30 cm`
B. `20 cm`
C. `40 cm`
D. `50 cm`

Answer

C

Explanation

For convex lens,
`1/v-1/-12=1/(+20) rArr v=-30 cm`
This image `I_1` is therfore, `(30+10) cm or 40 cm`
towards left of plane mirror. Therefore, second
image `I_2` (by the plane mirror) will be formed
`40cm` behind the mirror.