P is a point on the axis of a concave mirror. The image of P, formed by the mirror, coincides with P. A rectangular glass slab of thickness t and refractive index `mu` is now introduced between P and the mirror. For the image of P to coincide with P again, the mirror must be moved

Options

A. towards P by `(mu-1)t`
B. away from P by `(mu-1)t`
C. away from P by `t(1-1/mu)`
D. towards P by `t(1-1/mu)`

Answer

C

Explanation

Due to slab, object P will appear a distance `t(1-1//mu)` nearer to mirror. If image of object coincides with it, mirror should be shifted by `t(1-1//mu)` away from P.