A `20cm` thick glass slab of refractive index `1.5` is kept in front of a plane mirror. Find the position of the image (relative to mirror) as seen by an observer through the glass slab when a point object is kept in air at a distance of `40 cm` from the mirror.

Explanation

As thickness of glass slab is 20 cm and its `mu = (3//2)`, so shift produced by it will be
`x=d[1-(1)/(mu)]=20[1-(2)/(3)]=(20)/(3) cm`
(towards the mirror)

The image of object in the mirror is `(100)/(3)`cm from the mirror. The glass slab shift this image towards the observer by `(20)/(3) cm`
Therefore the position of the final image from the 100 20 80 mirror w.r.t observer is `(100)/(3) -(20)/(3) =(80)/(3) cm`