What is mirage ? Give a reason for its formation ?
Hot sand (Rarer medium)
MIRAGE : When it is very hot, an inverted image of tree is seen which is ‘illusion of eye’ (gives a false impression) of water under the tree. This is called a MIRAGE.”
REASON: Sand becomes very hot during hot noon, the layers of air in contact become rarer (expand) while upper layers of air are still at comparatively low temperature and are denser medium.
When rays of light from DENSER to RARER medium (starting from tree) are bent away from normal when refracted from Rarer to Denser medium (going towards eye) bend towards normal and a tree appears INVERTED.