Question

What is a mirage? Explain the conditions under which it is seen.

Answer 1

Hint: In order to solve this problem we will first see the physical meaning of the term mirage. We will further understand the phenomenon involved behind the appearance of mirage and also the conditions required for the appearance of mirage.

Complete Step-by-Step solution:
Mirage is an optical illusion brought on by the phenomena of absolute internal light reflection. Mirage arises on a humid sunny day and produces an impression of water. But when we reach there, nothing seems to be there.
On a hot day, earth’s temperature on the surface increases. This leads to heating up of the air surrounding them. But the air present in the atmosphere will be cooler. Scientifically speaking, the refractive index of hot air is lesser than cold air. So when a light passes from cold air to hot air light tends to bend this is known as refraction.
As the light gets refracted it reaches to a point where the light tends to form ${90^0}$ angle. No more refraction takes place when it reaches 90, besides all the light gets reflected back. At this point of time trees look inverted which looks as if it is inverted on a pool. So this is total internal reflection.
Mirage is observed due to this phenomenon of total internal reflection which occurs due to atmospheric refraction.
Ideal conditions for a mirage are still air on a hot, sunny day over a flat surface, which absorbs the energy of the sun and gets quite hot. When these conditions exist, the air closest to the surface is hottest and least dense and the air density gradually increases with height.

Note- Mirage usually occurs in deserts. It occurs in hot atmospheric conditions. Total internal reflection is defined as: The phenomenon that occurs when the light rays travel from a denser optical medium to a denser optical medium. Optical fiber technology works on the same phenomenon of total internal reflection.