Question

What are the necessary conditions for total internal reflection to take place?

Answer 1

Hint: Total internal reflection occurs when light gets reflected totally into the same medium from the boundary interface. This happens for only a particular angle of incidence and a particular pair of mediums. This reflection is not the same as the reflection from the polished surface.

Complete step by step solution:
Total internal reflection:
When light travels from an optically denser medium optical rare medium such as from water to air, it gets reflected into the same medium when it incidents at the boundary interface. This phenomenon is called total internal reflection. This happens only when the angle of incidence is greater than a certain angle called the critical angle and it is denoted by C.
The necessary conditions for total internal reflection to take place:
1. The light must travel from an optically denser medium to an optically rarer medium i.e. medium 1 should have a higher refractive index compared to medium 2. Light travels slower in an optically denser medium compared to the optically rarer medium.
2. The angle of incidence must be greater than the critical angle. i.e.\[\angle i>\angle C\]
The critical angle is the minimum angle required for total internal reflection to occur. As the angle of incidence increases the angle of refraction also increases. For angle of incidence equal to the critical angle, angle of refraction will be${{90}^{{}^\circ }}$. If further increase the angle of incidence, the ray will get reflected into the same medium.
If \[\angle i<\angle C\] then light will get refracted into the second medium.
If \[\angle i>\angle C\] then light travels along the boundary interface of the two mediums.
If \[\angle i>\angle C\] then light gets reflected fully into the first medium.

Additional Information:
Examples of total internal reflection:
1. The shining of the diamond is observed because of the multiple total internal reflections of light.
2. Mirage: It is an example of total internal reflection, happening because of the different densities of the atmosphere near the surface.
3. Optical fibers: These are the best application of total internal reflection of light. Light is launched at an angle greater than the critical angle so that light traveling through the fiber suffers the total internal reflection.

Note: The phenomenon of total internal reflection happens only when light travels from an optically denser medium to an optically rarer medium and it is not observed when light travels from optically rarer medium to optically denser medium. When the light is incident at an angle equal to a critical angle then the light travels along with the interface of the medium.