Mirage is formed by total internal reflection in desents where due to heating of earth, refraction index of air near the surface of earth becomes lesser than above it.

The Mirage and Total Internal Reflection

The phenomenon of a mirage is a common optical illusion that occurs due to the bending of light rays in the Earth's atmosphere. It is often seen in deserts or on hot roads and appears as a shimmering pool of water or an image of an object that is not actually there. The mirage is formed due to total internal reflection.

What is Total Internal Reflection?

Total internal reflection occurs when light travels from a denser medium to a less dense medium and is incident at an angle greater than the critical angle. The critical angle is the angle of incidence at which the angle of refraction becomes 90°. When light is incident at an angle greater than the critical angle, it is reflected back into the denser medium instead of refracting into the less dense medium.

How does Total Internal Reflection cause a Mirage?

In the case of a mirage, the air near the ground is hotter than the air above it. This temperature difference causes a gradient in the refractive index of the air, which bends the light rays. As light travels from a denser medium (the ground) to a less dense medium (the air), it is refracted away from the normal. If the angle of incidence is greater than the critical angle, the light is reflected back into the ground.

The observer's eye receives the reflected light, producing an image of the object on the ground. Since the light is reflected, it appears as though the object is above the ground, creating the illusion of a shimmering pool of water or an image of an object that is not actually there.

Conclusion

In conclusion, the mirage is formed due to total internal reflection. The temperature difference in the air near the ground causes a gradient in the refractive index of the air, which bends the light rays. When the angle of incidence is greater than the critical angle, the light is reflected back into the ground, creating the illusion of a mirage.