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Question
Why is the colour red used as a sign of danger?
Solution
In the visible light, the wavelength of red light is longest, the light of red colour is scattered least by the air molecules of the atmosphere and therefore the light of red colour can penetrate to a longer distance. Thus, red light can be seen from the farthest distance as compared to the other colours having the same intensity. Hence, it is used for danger signal so that the signal may be visible from the far distance even in fog, etc.
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