Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 29/11/2007 21:27:15
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Is transparency a feature of all fluids, and why?
Chris
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If an object is transparent it just means that it does not interact very much with the radiation that you are illuminating it with (light is the most familiar) and so does not absorb it or reflect it. This is not a property of fluids specifically because there are many liquids (and gases) that are not transparent. For example nitrogen dioxide is a dark brown gas and mercury is conducting so it cannot be transparent because it reflects. There are also many solids like diamond that are transparent. Although the earth's atmosphere is transparent to light on a clear day, it is not transparent to many longer wavelengths in the infra red spectrum or shorter wavelengths in the ultra violet spectrum. When the radiation is of a much shorter wavelength like Xrays and gamma rays just about everything is reasonably transparent because the radiation can zip right through the electron shells of the atoms so you need big heavy atoms like lead and lots of it to stop that sort of radiation.
Down in the long wave infra red region almost nothing is transparent because the frequencies are related to the atomic vibrations in materials at room temperature.
At radio wavelengths insulating materials are mostly reasonably transparent but conducting materials reflect the waves. Water is a real problem because it is always just a bit conducting and so absorbs quite strongly (that's why microwave cookers work).
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I think lead is the most interesting case, you can have glass that is beautifully clear containing 40% lead
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I think lead is the most interesting case, you can have glass that is beautifully clear containing 40% lead
Ok, but it's not in the metallic form there, it's lead oxide/silicate
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Is transparency a feature of all fluids, and why?
Chris
As Soul Surfer said, it's not true; however many fluids are transparent, why? In the case of gases it's quite obvious: usually atoms and molecules don't have absorption bands in the visible spectrum. About liquids, with a few exceptions, a liquid is such because it's made of molecules which are weakly interacting (with respect to the atoms in the molecule) so the molecules cannot have a "collective behaviour" and so they cannot split their energetic levels in many other sub-levels as in the case of solids; as result, a liquid absorption spectrum is almost entirely due to their single molecules, which don't absorb much (generally) in the visible spectrum.