Previous Year Question
The reason of mirage is
interference of light
diffraction of light
polarisation of light
total internal reflection of light
Correct Answer: D
Detailed Solution
A Mirage is an optical phenomenon commonly observed in hot regions, particularly over deserts or heated roads.
Under strong sunlight, the air close to the ground becomes very hot. Hot air is relatively less dense and has a lower refractive index, while the comparatively cooler air above it has a higher refractive index.
Light coming from a distant object passes through air layers having different temperatures and refractive indices and continuously bends away from the normal due to refraction. At a certain stage, the angle of the ray may become sufficiently large for it to turn upward; in school-level optics, this is explained in terms of Total Internal Reflection.
The observer perceives these rays as coming from the ground, so the brain traces them backward and forms a virtual inverted image of the distant object below the ground. This produces the illusion of water or a shining surface at a distance.