The ability of a medium to refract light is expressed in terms of its optical density. Optical density has a definite connotation. It is not the same as mass density. On comparing two media, the one with the large refractive index is optically denser medium than the other. The other medium with a lower refractive index is optically rarer. Also the speed of light through a given medium is inversely proportional to its optical density.
Generated by claude-sonnet-4-6 · 2026-06-15 06:50 · grounding stimulus
Model Answer
(i) Refractive index, $n = \dfrac{c}{v}$
$$v = \frac{c}{n} = \frac{3 \times 10^8}{2.42} = 1.24 \times 10^8 \text{ m/s}$$
Speed of light in diamond = 1.24 × 10⁸ m/s
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(ii) Higher refractive index → optically denser → lower speed → smaller angle of refraction.
Order of refractive indices: Carbon disulphide (1.62) > Glass (1.5) > Water (1.33)
∴ Increasing order of angle of refraction:
Carbon disulphide < Glass < Water
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(iii) (The sub-question (A)/(B) options are not printed in the passage provided. Please include the full text of option A or B for a complete answer.)
Source: Light – Reflection and Refraction, Refraction of Light / Refractive Index
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Explanation
- (i) Use $n = c/v$, rearrange to $v = c/n$. Standard 1-mark numerical — show formula and substitution.
- (ii) From the passage: higher refractive index = optically denser = slower light. By Snell's law, denser medium refracts light closer to the normal (smaller refraction angle). So the medium with the highest n gives the smallest angle of refraction. Rank accordingly.
- (iii) The options A/B were not provided in the question; a student must copy those from their paper and answer accordingly. Do not leave it blank in the actual exam.