Give reasons :
(i) The sky appears dark to passengers flying at very high altitude.
(ii) 'Danger' signal lights are red in colour.
Generated by claude-sonnet-4-6 · 2026-06-15 06:53 · grounding rag
Model Answer
(i) At very high altitudes, there are very few air molecules and fine particles to scatter sunlight. Since scattering is not prominent at such heights, the sky appears dark to passengers flying at very high altitudes.
(ii) Red light has the longest wavelength among visible colours and is least scattered by fog or smoke. Therefore, red danger signals can be seen clearly from a long distance without losing their colour.
Source: Chapter 10, Section 10.6 – Scattering of Light
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Explanation
- Both answers come directly from Section 10.6.2 of the textbook — quote those lines closely in the exam.
- For (i), the key phrase is "scattering is not prominent at very high altitudes" — no particles = no blue scattered light = dark sky.
- For (ii), the key idea is "red is least scattered", so it travels farther without being diffused, making it ideal for danger/warning signals.
- Examiners look for the word "scattering" in both answers — don't omit it.