Among the following which one is not due to the phenomenon of total internal reflection?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Dispersion of light
Total internal reflection happens when light goes from a denser to a rarer medium at an angle of incidence greater than the critical angle; then all the light is reflected back into the denser medium.
Option (1) Mirage — Due to total internal reflection. On a hot day the air near the ground is hotter and optically rarer; light from a distant object bends gradually and is totally reflected near the ground, giving an inverted image like a pool of water.
Option (2) Spectacular brilliance of diamond — Due to total internal reflection. Diamond has a very small critical angle (about \( 24^\circ \)), and its cut faces make light entering it suffer repeated total internal reflections before it leaves.
Option (3) Optical fibers — Due to total internal reflection. Light travels along the fibre core by repeated total internal reflection at the core-cladding boundary.
Option (4) Dispersion of light — Not due to total internal reflection. Dispersion is the splitting of white light into colours because the refractive index depends on wavelength, so each colour is refracted through a different angle. This is the phenomenon asked for.
NCERT (2026-27):
Summary – “… For i > ic, total internal reflection occurs. Multiple internal reflections in diamond (ic ≅ 24.4°), totally reflecting prisms and mirage, are some examples of total internal reflection. Optical fibres consist of glass fibres coated with a thin layer of material of lower refractive index. Light incident at an angle at one end comes out at the other, after multiple internal reflections, even if the fibre is bent.”