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Q108 (IAS/1995) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Geometrical optics Answer Verified

Assertion (A) : A diamond sparkles more than a glass imitation cut to the same shape. Reason (R) : The refractive index of diamond is less than that of glass. In the context of the above two statements, which one of the following is correct ?

Result
Your answer: —  ·  Correct: C
Explanation

The assertion is correct: properly cut diamonds sparkle more than glass imitations because diamond’s optical properties (high refractive index and strong dispersion) produce greater internal reflection and ‘fire’. The refractive index of diamond is 2.42 [1], while typical glass refractive indices are around ~1.5–1.6 [2]. The reason statement is incorrect: it claims diamond’s refractive index is less than glass, which contradicts the data. Moreover, gemological discussions note that diamond’s high refractive index and dispersion (wavelength-dependent refraction) are responsible for enhanced brilliance and spectral colour separation (fire), which explain the greater sparkle compared to glass. Thus A true, R false.

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > QUESTIONS > p. 150
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > 9.3.2 The Refractive Index > p. 149
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