Fig. 9.1 shows a simplified diagram of an optical fibre. (a) Name the process by which light travels along the fibre. [1] (b) Explain the role of the claddi...

(a) Name the process [1]

Total internal reflection (TIR) [1]

The light bounces off the inner surface of the core at each reflection point, staying entirely within the fibre as it travels along its length.

(b) Role of the cladding around the core [2]

The cladding has a lower refractive index than the core. [1] This ensures that when light hits the core-cladding boundary at an angle greater than the critical angle, total internal reflection occurs and the light stays within the core. [1] Without cladding, light could leak out where fibres touch or where the surface is scratched, and the signal would be lost.

(c) Why the core must have a higher refractive index than the cladding [1]

For total internal reflection to occur, light must travel from a more optically dense medium (higher refractive index) to a less optically dense medium (lower refractive index). [1] If the core had a lower refractive index than the cladding, light would refract into the cladding rather than being reflected back, and the fibre would not work.

(d) Two advantages of optical fibres over copper cables [2]

1. Optical fibres can carry much more data at the same time (higher bandwidth), so they support faster communication. [1]
2. Optical fibre signals do not suffer from electrical interference, making them more reliable. They are also more secure (harder to tap), lighter, and thinner than copper cables. [1]