Question

A mirage occurs because :

• A. the hot ground acts like a mirror
• B. the refractive index of atmosphere decreases with height
• C. the refractive index of atmosphere increases with height
• D. the refractive index remains constant with height

Answer 1

The correct option is C the refractive index of atmosphere increases with height

A mirage occurs because the refractive index of the atmosphere increases with height.

Mirages are examples of total internal reflection. The conditions most likely to produce a mirage in the desert would be a layer of hot air lying immediately above the ground with cooler air above it (this is quite usual during the day because the ground becomes so hot). The refractive index keeps on increasing as we go up. The incident light from the object gets total internally reflected and reaches the observer's eyes if the angle of incidence is greater than the critical angle of the adjacent layer. Thus we see a reflection of the sky and other objects on the ground.