What is mirage? With a neat labelled diagram , explain the conditions under which it is seen.

Explanation

Due to the changes in refraction of light, the light rays coming from a distant object appear to be coming from the image of the object inside the ground. This is called a mirage. When the earth's surface is heated by the sun, the temperature of air increases. This produces a layer of hot air of lower density ( mass per unit volume) and lower refractive index at the surface. Hot air works as an optically rarer medium relative to cool air. When the temperature changes rapidly in the vertical direction , as refraction of light takes place, the angle of refraction changes continuously.

The rays of light from the top of an object such as a car or tree cross the rays from the bottom of the object on their way to the observer's eye. Hence, an inverted image is formed below the object's true position and downward towards the surface in the direction of air at higher temperature.In this case, some rays of light bend back up into the denser air above. Mirage produces an impression of water near the hot ground.