What optical phenomenon accounts for the formation of mirages observed on hot desert roads or asphalt surfaces during bright sunny days?

💡 Solution & Explanation

Mirages occur when air near the ground becomes much hotter than the air higher up, creating a vertical temperature gradient that decreases air density and refractive index closer to the ground. Light rays traveling downwards from the sky enter layers of progressively lower refractive index, bending away from the normal until the angle of incidence exceeds the critical angle, causing total internal reflection upwards toward an observer. Incorrect options invoke diffraction or interference which describe chromatic fringes or wave superposition rather than large-scale gradient refraction. Refractive index variations in the atmosphere also cause astronomical twinkling of stars.