The values of absolute refractive indices of kerosene and water are 1.44 and 1.33 respectively. Compare the two media on the basis of their
(a) optical density
(b) mass density
(c) relative speed of propagation of light.
What do you infer on the basis of above comparisons?
Generated by claude-sonnet-4-6 · 2026-06-15 06:51 · grounding rag
Model Answer
(a) Optical density: Kerosene (n = 1.44) has a higher refractive index than water (n = 1.33), so kerosene is optically denser than water.
(b) Mass density: Kerosene has less mass density than water (kerosene floats on water).
(c) Speed of light: Since $n = c/v$, higher refractive index means lower speed. So light travels slower in kerosene than in water.
Inference: Optical density and mass density are not the same. A medium can be optically denser yet have lower mass density (e.g., kerosene).
Source: Chapter 9, Section 9.3.2 — The Refractive Index
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Explanation
- The key point examiners look for is the distinction between optical density (linked to refractive index) and mass density (physical property). This is explicitly stated in the textbook note.
- For speed: use $n = c/v$ — higher n → lower v. So kerosene slows light more than water does.
- The inference must state clearly that optical density ≠ mass density. This is the central learning from this comparison.
- Keep each part brief; this is a 2-mark question, so one line per part plus one inference line is enough.