The phenomenon of “total internal reflection” is observed in which one of the following ?

Total internal reflection (TIR) occurs when light travels from an optically denser medium to a rarer medium and the angle of incidence exceeds the critical angle [t2][t4]. Diamond has a very high refractive index of approximately 2.42 [c1][t2]. This high refractive index results in a very small critical angle of about 24.4 to 25 degrees [t2][t4]. Because of this small critical angle, light entering a diamond is likely to undergo multiple internal reflections before it can escape, which creates the characteristic sparkling effect [t2][t4]. In contrast, the twinkling of stars is caused by atmospheric refraction and scintillation due to varying air densities [t1][t6]. Light passing through a lens involves standard refraction [c3][c5], and a glowing tube light operates on the principle of gas discharge and fluorescence rather than TIR.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > QUESTIONS > p. 150
2. [2] https://www.govinfo.gov/content/pkg/GOVPUB-C13-25e8f6a9029e9512530c959bd47f5642/pdf/GOVPUB-C13-25e8f6a9029e9512530c959bd47f5642.pdf
3. [3] https://science.uct.ac.za/sites/default/files/content_migration/science_uct_ac_za/1471/files/Astrophysics-Decoding-the-Cosmos-Judith.A.Irwin_.pdf
4. [4] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > 9.3.8 Power of a Lens > p. 157
5. [5] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > p. 134