What is the reason for formation of Mirage in desert?
Both Refraction and Total internal reflection of light
In a desert, the ground heats the air just above it, creating a stack of air layers whose density (and refractive index) increases with height. Light from the sky travelling downward repeatedly bends away from the normal as it enters successively rarer (hotter) layers — this is continuous refraction.
Eventually the angle of incidence exceeds the critical angle \(\theta_c\), where \(\sin\theta_c = \dfrac{n_2}{n_1}\), and the ray undergoes total internal reflection, curving back up to the observer's eye. The brain projects it straight, producing the watery image on the sand.
Hence a mirage involves both refraction and total internal reflection of light.
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