Total Internal Reflection

Total internal reflection is one of the most interesting concepts in Physics. here we will learn about the concepts of this topic in depth along with various applications of total internal reflection.

What is Total Internal Reflection?

Consider the following situation. A ray of light passes from a medium of water to that of air. Obviously, the light ray will be refracted at the junction separating the two media. Since it passes from a medium of a higher refractive index to that having a lower refractive index, the refracted light ray bends away from the normal. At a specific angle of incidence, the incident ray of light is refracted in such a way that it passes along the surface of the water.

This particular angle of incidence is called the critical angle. Here the angle of refraction is 90 degrees. So how is the critical angle related to total internal reflection? Any light rays with angles of incidence greater than the critical angle will not cross the water medium at all, will they? They will be “reflected” back into the same medium. This is Total Internal Reflection. The figure below will clarify this concept.

Total Internal Reflection

Total Internal Reflection

Applications of Total Internal Reflection

Diamonds which are used as jewelry are designed and cut in such a way to maximize the amount of light which experience total internal reflection. This makes diamond trap most of the light that enters it, which then undergo several total internal reflections before leaving the diamond, making it supremely shining. Diamond has a very high refractive index.

Optical fibers which are used mainly in telecommunication are another important application of total internal reflection. Optical fibers have revolutionized the speed with which signals are transferred, not only across cities but across countries and continents making telecommunication one of the fastest modes of information transfer.  Optical fibers are also used in endoscopy.

There are certain rain sensors which control windshield wipers on vehicles that apply the principles of total internal reflection. Certain kinds of touch screens on cameras also use this principle.

It is one of the finest breakthroughs in the field of communications.

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Practise This Question

In the figure shown, for an angle of incidence 45^{\circ}at the top surface, what is the minimum refractive index needed for total internal reflection at vertical face