Explain the formation of mirage? (AS1)

Definition: Mirage is the optical illusion; the water appears at the distance but when we go there we don’t find any water. It occurs due to Total Internal Reflection.

Formation:

1. During hot summer days air just above road is very hot and air at higher altitudes is cold.

2. It means that temperature decreases with height. As a result density of air increases with height.

3. We know that refractive index of air increases with density. Thus refractive index of air increases with height.

4. So cooler air has higher refractive index than the hotter air just above the road.

5. Therefore light travels faster through thinner hot air than dense cold air.

6. When light from tree passes through the medium just above ground whose refractive index decreases towards ground it suffers total internal reflection and takes the curved path.

7. This appears as the ray is reflected from the ground. Hence we feel illusion of water being present on the road.

8. The inverted virtual image seen by observer is called as the mirage.

The figure below depicts the formation.