Mirages are optical phenomena that occur due to the bending or refraction of light as it passes through air layers with varying temperatures. Although light generally travels in straight lines, its path can be bent when it encounters a change in the refractive index of the medium it is passing through. In the case of mirages, this bending of light creates an illusion that causes objects to appear distorted or elevated.
Here's a simplified explanation of how mirages occur:
Temperature Gradient: Mirages are commonly observed in areas with significant temperature variations, such as hot deserts or asphalt roads on a sunny day. These regions often have a temperature gradient, with the air near the ground being hotter than the air at higher altitudes.
Refractive Index Gradient: As light travels from one medium (such as air) to another (such as hotter air), its speed and direction change due to the variation in the refractive index of the medium. The refractive index of a medium is a measure of how much it can bend light.
Light Bending: When light passes from a cooler region to a hotter region, it moves from a denser medium to a less dense one. This transition causes the light to bend away from the normal (the line perpendicular to the surface). This bending is known as a downward refraction.
Total Internal Reflection: In certain conditions, when the refractive index gradient is steep enough, the downward refraction can become so significant that light rays bend enough to create a phenomenon called total internal reflection. Total internal reflection occurs when the angle of incidence is larger than the critical angle, causing the light to be entirely reflected back into the denser medium.
Virtual Image Formation: When total internal reflection occurs near the ground, it can create a virtual image of an object located above the ground. This virtual image appears to be elevated and displaced from its actual position, leading to the mirage effect.
The type of mirage observed depends on the specific atmospheric conditions. For example, a "inferior" mirage creates the illusion of water or a reflective surface on the ground, while a "superior" mirage can make objects appear higher than they actually are.
In summary, mirages occur due to the bending of light caused by variations in temperature and the refractive index of the air. These optical illusions result in the distorted or elevated appearance of objects that we perceive in mirage phenomena.