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(i) Name the phenomenon on which the working of an optical fibre is based.
(ii) What are the necessary conditions for this phenomenon to occur?
(iii) Draw a labelled diagram of an optical fibre and show how light propagates through the optical fibre using this phenomenon.

Last updated date: 24th Jul 2024
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Hint: Optical fibre is a data communication system that uses light waves that pass over a long fibre, which is normally made of plastic or glass. Metal wires are used for optical fibre communication transmission since signals pass with less disruption.

Complete answer:
Electromagnetic interference has little effect on optical fibres. The cumulative internal reflection of light is used in the fibre optical cable. The fibres are designed to aid in the propagation of light along with the optical fibre, depending on the strength and transmission distance requirements. Long-distance transmission is done with single-mode cable, whereas shorter distances are done with multimode fibre. These fibres' exterior cladding needs more shielding than metal wires.
(i)Optical fibres operate under the principle of absolute internal reflection.
The absolute internal reflection theorem governs the operation of the optical fibre. Light rays can relay a large volume of data, but there is a drawback: light rays travel in straight lines. So harnessing this advantage would be difficult unless we have a long straight wire with no twists. The optical cables, on the other hand, are constructed to bend all light rays inwards (using TIR). Light rays travel indefinitely, scattering off optical fibre walls and sending data from one end to the other. While light signals fail over distances, depending on the purity of the material used, the loss is significantly less than with metal cables.
(II) Total internal reflection occurs when the incidence ray's angle exceeds the critical angle. The critical angle is the angle formed by the incidence ray with the normal above which absolute internal reflection occurs.
When a light ray travels from a denser to a rarer medium at a greater angle than the critical angle, it is fully mirrored in the first (denser) medium. Total internal reflection is the term for this condition.
(a) A ray of light must travel from a denser to a rarer medium.
(b) The incidence angle must be greater than the critical angle (i.e., I > C).
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Note: A flexible, clear optical fibre (or fibre in British English) is made by drawing glass (silica) or plastic to a diameter slightly larger than that of a human hair. Optical fibres are most often used to relay light between the fiber's two ends, and they're widely used in fiber-optic communications, where they allow transmission over longer distances and at higher bandwidths (data transfer rates) than electrical cables.