23-мәтін

Ultraviolet and infrared

Visible light covers a very small part of the electromagnetic spectrum. Just above and below the visible light range are ultraviolet and infrared light. The «ultra» in ultraviolet tells us that this light lies at frequencies higher than that of violet light lies; and the «infra» in infrared tells us that this light lies at frequencies lower than red.

Ultraviolet has a shorter, and infrared has longer wavelengths than visible light. The radiations were discovered long before anyone thought of electromagnetism. When light was passed through a prism and formed a spectrum on screen, scientists found that heating effect occur beyond the edges of the visible light spectrum. Ultraviolet radiation produces many effects, some useful and some unpleasant. A certain amount of ultraviolet radiation is good for our health. It helps to form vitamin В in the skin. Ultraviolet light always kill microbes, and for that reason is used in hospitals and to sterilize food.

Direct ultraviolet radiation is very bad for the eyes. This is one reason why it is dangerous to look directly at the Sun. On the other hand, the human eye is quite capable of dealing with normal doses of scattered ultraviolet light.

Infrared energy is being used in automatic regulation of chemical and biological processes, temperature measurement and control during manufacture of textiles, plastics and metal. New applications are appearing in navigation and aviation, weather research and numerous scientific projects. Infrared energy is in use all around us. Infrared techniques are of great value in many industrial applications and are considered indispensable. (by A. Kovalenko)