Look , there is water on road.
This is natural when you are driving in summer. Water seems to appear on roads in summer because of a phenomenon called a Mirage. Mirage forms due to phenomenon called Total Internal Reflection.
Total internal reflection happens when a light ray traveling inside a denser medium (like water or glass) hits the boundary with a less dense medium (like air) at a steep enough angle and gets completely reflected back into the denser medium — instead of passing through the boundary.
A mirage is a natural phenomenon where light rays are bent to produce a displaced image of distant objects or the sky. In the case of roads, it appears as if there’s a puddle reflecting the sky. But the road is dry. Why?
The Science Behind It: Total Internal Reflection
To understand a mirage, we first need to understand a key concept in physics: Total Internal Reflection (TIR).
Total Internal Reflection occurs when:
- Light travels from a denser medium (like glass or water) to a less dense medium (like air).
- If the light hits the boundary at a shallow angle, it bends and passes through — this is refraction.
- But if the light hits at a steeper angle (beyond a certain point called the critical angle), it doesn’t pass through at all. Instead, it bounces back entirely into the denser medium — this is total internal reflection.
How Does This Cause a Mirage?
Let’s break it down step-by-step:
- Hot Road, Hotter Air: On a sunny day, the surface of the road heats up intensely. The air just above it becomes much hotter than the air even slightly higher up.
- Layers of Air With Different Temperatures: This creates layers of air with varying densities — cooler air above, hotter air below.
- Light Travels From Cool to Hot: Light from the sky travels downwards through these layers. As it goes from cooler (denser) air to hotter (less dense) air, it bends away from the normal — a process known as refraction.
- Eventually, It Reflects Back: At a certain point, the angle of the light becomes steep enough that it doesn’t refract anymore. Instead, it reflects — just like in TIR. This reflected light travels upward into your eyes.
- Your Brain Gets Fooled: Your brain assumes light travels in a straight line, so it “traces” the reflected light back in a straight path — making it appear as though it’s coming from the ground. The result? A shiny surface that looks like water.
So, Is There Any Water on the Road?
No. It’s an optical illusion. The road is completely dry — your eyes and brain have just been tricked by physics!
Where Else Do We See Total Internal Reflection?
Total Internal Reflection isn’t limited to hot roads. It’s used in some truly fascinating and useful ways:
- Diamonds: Diamonds sparkle brilliantly because of how they’re cut to ensure multiple internal reflections. This keeps light bouncing inside until it exits dramatically, creating that signature sparkle.
- Optical Fibers: These fibers carry light signals over long distances — like your internet data — using TIR. Light keeps bouncing inside the fiber with virtually no loss.
- Mirage-like illusions in deserts: The same principle causes distant objects to appear distorted or flipped in hot deserts.
Name : Abhishek Agrawal
Department: Physics Foundation
Narayana Jaipur Center (NIHQ)