Question

A stratight rod partially immersed in water seems bent. Its reason

Answer 1

This phenomenon occurs due to property of light called refraction of light.When you immerse a stick in water,you are actually putting in from rarer medium to denser medium.When the rays of light pass from rarer medium to denser medium they move towards the normal.So the part of stick immersed in water appears to be broken towards the normal drawn at the interface.Hence a stick appears to bend when immersed in water.And it appears short because you feel it is raised up in the water(again the reason is the same).

Answer 2

When light enters from Air (rarer medium) to denser medium(water) there is a change in speed of light and hence it bends.
Therefore the rod appears bent.