An optical illusion which occurs mainly in deserts during hot summer i

An optical illusion which occurs mainly in deserts during hot summer is based on the principle of

Reflection

Interference

Dispersion

Total internal reflection

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This question was previously asked in

UPSC NDA-1 – 2017

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Optical illusions like mirages, which occur in hot deserts or over hot surfaces, are caused by the refraction and subsequent total internal reflection of light as it passes through layers of air with different temperatures and densities. The air near the hot ground is less dense and has a lower refractive index than the cooler air above. As light rays from the sky or distant objects travel downwards into the hotter, less dense layers, they bend upwards away from the normal. If the angle of incidence becomes greater than the critical angle, total internal reflection occurs, causing the light rays to be reflected upwards towards the observer’s eyes. The brain perceives these rays as coming from below, creating the illusion of a reflection, often resembling a pool of water.

– Mirages are caused by the bending of light (refraction) due to varying refractive indices in air layers of different temperatures.
– Total internal reflection occurs when light travels from a denser medium to a less dense medium at a sufficiently large angle of incidence.
– In hot conditions, air near the surface is hotter and less dense, creating conditions for total internal reflection of light traveling from cooler, denser air above.

Reflection is bouncing off a surface. Interference involves the superposition of waves. Dispersion is the splitting of light into its constituent colours based on wavelength. While refraction is the initial cause of bending, total internal reflection is crucial for the significant upward bending that creates the mirage image seen by the observer.

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