Practice portal › Electromagnetic Waves › Uses of the Bands, and lambda nu = c
Asked in GSEB Board July 2023 · Uses and atmospheric effects
Idea: to kill a micro-organism with radiation you must damage the molecules it needs in order to divide, and the radiation must reach it in the water instead of simply warming it.
Ultraviolet at about 250 nm is absorbed strongly by DNA, and that absorption breaks the strands so the cell can no longer reproduce.
Water is fairly transparent at that wavelength, so a low-pressure mercury lamp set in the flow sterilises the water as it passes, and adds no chemicals to it.
So ultraviolet rays are used.
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