A slab of glass of refractive index `1.5` and thickness `3cm` is placed with the faces perpendicular to the principle axis of a concave mirror. If the radius of curvature of the mirror is `10cm`, the distance at which an object must be placed from the mirror so that the image coincides with the object is

Options

A. `9cm`
B. `10cm`
C. `11cm`
D. `12cm`

Answer

C

Explanation

Shift of mirror towards object `=3(1-(1)/(3//2))=1cm`
If object and image coincides, for this object must be placed at centre of curvature of concave mirror i.e. at distance `10cm P^'`.
The distance O from actual mirror i.e. `PO=11cm`