Physics
(a) Name the electromagnetic radiations which are used for sterilising water in a water purifier.
(b) State any one property of the radiations mentioned by you in part (a).
(c) Why are the danger signals red in colour?
Spectrum
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Answer
(a) Ultraviolet radiation.
(b) Ultraviolet radiation produces fluorescence on striking a zinc-sulphide screen.
(c) Red light has the longest wavelength among visible colours, so it is scattered the least by air molecules. This allows it to travel the farthest without losing intensity. That’s why red is used for danger signals, it stays visible from a long distance, even in fog or mist.
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