Can you see total internal reflection?

It is an optical illusion due to which we see a layer of water at a short distance in a desert

But there is actually no water at all

The mirage produced is a result of Total Internal Reflection

The total internal reflection of light occurs in the upward direction caused by atmospheric refraction

Let us start by understanding what Total Internal Reflection is

When light travels from one medium to another, the path of light bends depending on the optical density of the medium

When light travels from a rarer to a denser medium, the light gets refracted such that it bends towards the normal

When light travels from a denser to a rarer medium, the light gets refracted in such a way that it bends away from the normal

Let us now consider an incident ray whose incident angle is continuously increased

At one point, as the incident angle is increased, the refracted ray grazes along with the interface

At this point, the refracted ray makes an angle $90^o$ with the Normal. This angle of incidence is known as the critical angle

Upon further increasing the incident angle, the refracted ray goes back to the previous medium after reflection

The incident ray goes back to the previous medium if the angle of incidence is greater than the critical angle

The critical angle is the angle of incidence for which the refracted ray grazes the surface of the boundary between the two media

Let us now try and understand total internal reflection with the help of an experiment

For the experiment, we pour some water in a bottle and add some dettol to it

We then take a laser pen and direct the laser at the water mixed with Dettol inside the bottle

The water mixed with Dettol inside the bottle acts as the denser medium while the air outside is the rarer medium

We keep changing the angle of incidences of the laser until we can see the laser being completed reflected back

We will find that the laser light is reflected back into the dettol water

For all angles less than the critical angle the light does not reflect back

The phenomenon in which we find the laser light being reflected back is what we call the total internal reflection

Revision

Total internal reflection is the phenomenon in which light is reflected back to the previous medium

We can understand total internal reflection through a simple experiment with water,dettol, and laser light

When laser light is shined upon the water mixed with dettol, for a particular angle of incidence we find the light reflects back into the medium

The End