CBSE Class 12-science Answered

Mirage is an optical illusion caused due to Total Internal Reflection.It occurs during summers and especially in deserts.
For a certain column of atmosphere the pressure,temprature and density increases with height from the earth's surface.So, the light rays coming from an object will suffer continuous refraction as it will move from a denser to a rarer medium to reach our eyes.Hence,the angle of incidence gets increased because the refracted rays move away from the normal. A gradual increase in the angle of refraction brings a situation where it exceeds the critical angle.Henceforth, at that level the total internal reflection occurs and the ray of light returns back in the same medium,so an image is formed which is inverted.
This is mirage.