Total internal reflection is defined as the reflection of light ray within the medium, such as water from the surrounding surface and back to the medium. For total internal reflection to take place, the critical angle must be less than the angle of incidence.
Conditions for total internal reflection
Two conditions for total internal reflection are given below:
- The ray of light should always travel from a denser medium to rarer medium.
- The angle of incidence in the denser medium should be greater than the critical angle of the media.
Applications of total internal reflection
Following are the applications of total internal reflection:
The sparkling of diamonds is because of the phenomenon of total internal reflection. The faces of the diamond are cut in such a way that when the light enters the diamond, the light ray undergoes multiple reflections. Also, the difference between the refractive index of a diamond and the refractive index of air is very large. The diamonds are cut in specific ways, such that the light rays are incident with the angle of incidence more than the critical angle. Thus, the sparkling effect in the diamond is possible when the light ray suffers multiple total internal reflections.
Fibres used in optical fibre are made from the material that has a high refractive index. It consists of parts such as core, cladding, buffer, and jacket. The core is the innermost part while the jacket is the outermost part of the optical fibre.
The principle behind the optical fibre is that when the light ray enters the core of the glass fibre from one end such that the angle of incidence is greater than the critical angle, the light ray suffers multiple total internal reflections. The emergent ray is obtained after these total internal reflections from the other end of the fibre.
Optical fibres find applications in optical communications and in endoscopy.
Mirage is an everyday example of total internal reflection, which is commonly noticed during sunny days on the roadways. It is an optical illusion of water which is a result of the reflection of light through a non-uniform medium. It is observed that when a puddle of water is found at a certain distance and when that distance is covered, it moves further away. This appearance of water is an illusion.
The occurrence of this optical illusion can be explained through total internal reflection. The role of the sun is to heat up the surrounding air to a temperature which is higher than the average air temperature. Since the hot air is denser than the cooler air, a non-uniform medium is created on the roadways. As the light rays travel through a uniform medium and reaches this non-uniform medium, it experiences refractions resulting in a mirage.
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