Question

Explain why a straight Stick appears to be bent when dipped in water ?

Answer 1

because the stick from air a rarer medium goes to water a denser medium so due to the refractive index it tends to bend

Answer 2

This is due to refraction of light from water to air.The rays of light coming from tip of the stick in water when passes from water to air, bend away from the normal and appear to be coming from a point above the tip of the stick.It is the virtual image of the tip of the stick.
The immersed part of the stick appears to be raised and therefore bent when dipped in water.

Hope it helps you