CBSE Class 10 Science 2020 · Paper 31/5/1 · Question 24(b)
Give reasons :
- (a)Red colour is selected for danger signals.
- (b)The sky appears dark in space.
- (c)The time difference between actual sunset and apparent sunset is about 2 minutes.
Answer
Red is scattered least; space has no air to scatter light; atmospheric refraction shows the Sun about 2 minutes after actual sunset.
(a) Red light is scattered the least by fog or smoke, so a red signal can be seen in the same colour from a long distance.
(b) In space there is no atmosphere, so there is no scattering of sunlight; no scattered light reaches the eye from the sky, so the sky appears dark.
(c) Because of atmospheric refraction: sunlight bends towards the Earth as it passes through the atmosphere, so the Sun appears above the horizon even after the actual sunset, for about 2 minutes.
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