Q1. [2] medium thorough-understanding
[short_answer] The refractive indices of air, ice, and ruby are approximately 1.0003, 1.31, and 1.71 respectively. Rank these three media in increasing order of the speed of light passing through them. Explain your reasoning using the relationship between refractive index and speed of light.
Generated by claude-sonnet-4-6 · 2026-06-26 01:14 · grounding rag
Model Answer
The relationship is: $n_m = \dfrac{c}{v}$, so a higher refractive index means a lower speed of light.
Increasing order of speed of light:
Ruby (n = 1.71) < Ice (n = 1.31) < Air (n = 1.0003)
Since refractive index is inversely proportional to speed, light travels slowest in ruby (highest n) and fastest in air (lowest n).
Source: Chapter 9, Section 9.3.2 – The Refractive Index
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Explanation
- The key formula is $n_m = c/v$, meaning speed $v = c/n_m$. Higher refractive index → lower speed.
- Examiners expect you to state the inverse relationship clearly, then apply it to rank the three media correctly.
- Always write the ranking explicitly — don't leave it implied.