Figure shows a object placed in front of a lens of focal length `10` cm, at a distance `20` cm from the lens. On the other side, a convex mirror `(f=5cm)` (with same principle axis as that of lens) is placed such that all light rays after refracting through lens strike the mirror simultaneously. The distance between the mirror and the lens is:

Options

A. `5cm`
B. `10cm`
C. `30cm`
D. cannot be determined.

Answer

B

Explanation

`1/v-1/u=1/f`
`implies1/v=1/(-20)+1/10=(2-1)/20=1/20impliesv=20cm`
`f_("mirror")=5cmimpliesR_("minor")=10cm`.