Concept:The mirage in deserts is caused by total internal reflection of light in a medium where the refractive index changes gradually.
Explanation:During a hot summer day, the desert sand becomes extremely hot, heating the air just above the ground.
This hot air is less dense than the cooler air above it.
Since refractive index decreases with density, the lower layers of air have a smaller refractive index than the upper layers.
Light from a distant object (like a tree or the sky) travels downward through these layers.
As the light moves from a denser (cooler) layer to a rarer (hotter) layer, it bends away from the normal.
If the angle of incidence in the denser medium exceeds the critical angle
C, total internal reflection occurs near the hot ground.
The reflected light travels upward toward the observer’s eye, creating the illusion that the light is coming from below the ground.
This inverted image of the object appears as a pool of water or a shimmering patch, which is the signature of a mirage.
Answer:D. Total internal reflection
