alleryWhy are danger signals such as stop lights and fire engines coloured red?
ARed is the brightest colour across all cases
BRed is scattered least by fog and rain, so it is visible from afar
CRed is the rarest colour in the standard view
DRed activates the brain fastest in general usage
Answer & Solution
Correct answer: B. Red is scattered least by fog and rain, so it is visible from afar
1. Air molecules and water droplets scatter shorter wavelengths more.
2. Red has the longest wavelength in the visible spectrum.
3. So red light is scattered the least by fog, rain or smoke.
4. Red signals therefore travel farther through poor visibility.
5. Hence danger signs use red so people see them from far away.
_Source: syllabus Science Ch 11 'Human Eye and the Colourful World'_
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