Total Internal Reflection: Definition and Conditions for Total Internal Reflection

Mirage is formed due to total internal reflection in the following way:

• On a hot day, the air near the ground becomes extremely hot as compared to air above it since hot air is less dense than cooler air, which has a lower refractive index.

• Light from the sky travels toward hotter and less dense air near the ground. As this light enters the hotter layer, it will bend away from the normal because of the change in refractive index.

• In case the angle of light is steep enough, it will exceed the critical angle between two layers of air. The light, instead of bending, reflects back up as a result of total internal reflection.

• This reflected light reaches our eyes and gives an illusion of water on the road.

Let us take a look at the various applications of Total Internal Reflection in real life:

1. Total internal reflection is the foundational phenomenon used in modern telecommunications, internet cables and medical imaging. Light travels through thin and flexible fibres, which are made of glass and plastic. This light, then, undergoes Total internal reflection in the inner walls of the fibre, which allows travelling long distances with minimum loss. 

2. Mirage is a phenomenon that occurs due to the total internal reflection as light gets reflected between the layers of air.

3. Diamonds shine because of total internal reflection. The gem is cut at precise angles so that light, once it enters the stone, starts undergoing total internal reflection. 

4. Prisms utilize the concept of Total internal relection to reflect the light internally and change its direction without mirrors. Binoculars, periscopes and cameras, all use the concept of Total Internal Reflection.

5. Decorative lights use Total internal reflection to create visual effects like starry ceilings and glowing ornaments.

Yes, total internal reflection can occur in both sound and water waves, including light waves, since it follows the same principle. Whenever a light/sound/water wave travels from denser to rarer medium and strikes the boundary of the medium at an angle greater than critical angle, the wave entirely reflects back into denser medium rather than refracting. Sonar waves in submarine reflect back entirely from the water surface as it hits at a steep angle. In water, ocean waves approach beach and slow down because of shallower water. If a wave hits the boundary of deep and shallow water at a steep angle, these waves will reflect back towards the open ocean instead of breaking on shore.