A concave mirror of focal length `20cm` is placed inside water with its shining surface upwards and principla axis vertical as shown in Fig. Rays are incident parallel to the principa, axis of concave mirror. Find the position of final image.

Explanation

The incident rays will pass undeviated through the water surface and strike the mirror parallel to its principle axis. Thereofre for the mirror, object is at `oo`. Its image `A` (in figure) will be formed at foucus which is `20cm` form the mirror, Now that the interface between water and air, `d = 10cm`.
`:. d' = (d)/(((n_(W))/(n_(a)))) = (10)/(((4//3)/(1))) = 7.5cm`