The phenomenon used in optical fibre for transmission of light energy is

The correct answer is A) Total internal reflection. An optical fibre has a core with a higher refractive index than the surrounding cladding. When light hits the core-cladding boundary at an angle greater than the critical angle, given by sin(theta c) = n2/n1, it is reflected back into the core instead of escaping. Repeated reflections guide the light along the fibre, even around bends.

• B) Diffraction is the spreading of waves around obstacles or apertures. It does not guide light along a fibre.
• C) Scattering is a loss mechanism. Rayleigh scattering from microscopic density fluctuations causes attenuation, which limits the distance a signal can travel. It is not how transmission works.
• D) Refraction happens at the boundary, but refraction alone lets light bend out into the cladding. Guidance requires total internal reflection.

The concept links to the communication and ICT part of Science and Technology. For Mains GS-3, it connects to digital infrastructure, such as BharatNet's optical fibre rollout, and to why signal attenuation matters for rural connectivity.

Trap: Students pick refraction because it is the familiar bending-of-light idea. The examiner is testing the angle condition, which requires light to exceed the critical angle at the core-cladding interface.