Question

Mirage is an example of ________.

Answer 1

Hint: Mirage is an optical illusion that is generally caused due to heat from the sun in the desert areas. In mirage, the person sees a water source at a distance, but it is actually caused because the hot air from the surface of the land rises up and changes the density of the air around it. This causes the sunlight reaching the viewer’s eyes to distort.

Complete step by step answer
In hot areas, like a desert, the land is made up of sand which heats up very fast. When the sunlight falls into the sand, the temperature of the sand, as well as the air immediately surrounding it, increases. This temperature is more than the average temperature of the atmosphere. The hot air tends to rise up due to convection and the area above the surface of the land becomes less optically dense than the atmosphere.
We know that the refractive index of less dense air is less than that of more dense air. Thus, when sunlight travels from the upper atmosphere to the area with low air density, it travels from a medium of higher refractive index to a medium of lower refractive index. Some of the sun rays undergo Total internal Reflection and follow a curved path back to the viewer’s eyes.
This distorted image of the sun is shiny and is constantly moving due to the turbulent flow of air molecules. And due to the curved path, it looks as if it is coming from the ground. This looks similar to a water source.
Therefore, mirage is an example of Total Internal Reflection.

Note
Cold air is optically denser than hot air, this is why the air present just above the surface of the land has less optical density whereas the air present at a greater height has greater optical density. The light travels at different speeds in mediums with different optical densities. Total internal reflection occurs only when light travels from denser to rarer medium.