Which of the following examples are based upon the total internal ref…

The correct answer is Option (2) → (A), (C) and (D) only

Total internal reflection occurs when light goes from a denser to a rarer medium at an angle of incidence greater than the critical angle.

(A) Optical fibre — Correct. Light entering the fibre strikes the core-cladding boundary at more than the critical angle and is totally reflected again and again along the fibre.

(B) Twinkling of stars — Incorrect. Twinkling is due to atmospheric refraction: the changing density of the air keeps bending the starlight by slightly different amounts. No total internal reflection is involved.

(C) Mirage — Correct. Over a hot surface the air near the ground is rarer; light from a distant object bends more and more and is finally totally reflected upward, giving an inverted image like a reflection in water.

(D) Sparkling of diamond — Correct. Diamond has a very small critical angle (about \( 24^\circ \)), so light entering it is totally reflected many times inside before it comes out, which makes it sparkle.

NCERT (2026-27):
Summary – “… For i > i_c, total internal reflection occurs. Multiple internal reflections in diamond (i_c ≅ 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.”