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Infra-red radiations

  • The electromagnetic radiations beyond red and end of visible spectrum are called infra-red radiations.
  • White hot sources of light, such as sun, arc lamp, burning gases or any other material are best-suited for producing infra-red radiations of higher intensity. However, all living beings, animals plants or humans are infra-red emitters.
  • Infra-red rays produce heating effect, therefore they are used by the doctors for therapeutic purposes.
  • Infra-red radiations have a very long wave length, so they do not easily get scattered in fog or smoke. Thus they can be used for taking infra-rd photographs with suitable photographic plates and filters in foggy weather.
  • Since all hot objects are the emitters of infra-red radiations, therefore specially prepared devices, ie, night-vision devices can see the objects in darkness by receiving the infra-red radiations.
  • Infra-red radiations are used in surface to air missiles for tracking and destroying enemy planes. The on-board sensor and destroying enemy planes. The on-board sensor of infra-red radiations in the nose of missile detects the heat trail left by enemy plane to locate its position.
  • The region of spectrum which extends beyond violet colour of visible spectrum is called ultra-violet spectrum.
  • UV-radiations produce fluorescence in substances like zinc sulphide, barium sulphide, barium platinocyanide and quinine sulphate solution.
  • UV radiations produce chemical effect in silver salts.
  • UV radiations are absorbed by atmosphere and convert oxygen to ozone.
  • UV radiations can be detected by fluorescence.
  • Fluorescence is the phenomenon, where a substance absorbs an incident light of smaller wave length and then reflects a light of longer wave length.
  • UV radiations when absorbed by skin, stimulate the body to produce vitamin D, which is very good for growth of strong bones and teeth.
  • UV radiations are used to detect forgery of cheques or important documents, by erasing original writing. When such a document is placed under ultra-violet lamp, the alteration clearly shows up.
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