The Electromanetic Radiation Spectrum
The electromagnetic spectrum is a scale of frequencies (or alternatively, a continuous scale of wavelengths) defining the entire range of electromagnetic radiation. The scale extends from the lowest frequency (corresponding to the longest wave length) through to the highest frequency (corresponding to the shortest wave length). There is an inverse relationship between frequency and wave length. The electromagnetic spectrum is divided into frequency ranges (for example, ultraviolet, visible light, infrared, radiofrequency, and extremely low frequency) according to their actual use, their physical properties and their potential health effects.
The spectrum is generally categorized into two principal electromagnetic radiation types: non-ionizing radiation and ionizing radiation.
The Electromanetic Spectrum
The non-ionizing radiation spectrum
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Extremely low frequency (ELF) range
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Intermediate frequency (IF) range, defined by the World Health Organization as comprising frequencies from 300Hz to 10MHz, with an overlapping range within the radiofrequency range from 3KHz to 10 MHz.
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Radio frequency (RF) range – comprises a number of frequency ranges, including, amongst others, the cellular (mobile phone) and microwave (MW) ranges.
- Infrared (IR) range – this frequency range is usually divided into a number of sub-ranges that include far infrared, long infrared, intermediate infrared and short infrared.
Visible light (VI) range – can be perceived by the human eye.
- Ultraviolet (UV) range - Mainly emitted by the sun, the UV range is divided into 3 frequency ranges: UVA, UVB and UVC. Of these, UVA and part of UVB is within the non-ionizing radiation range. UVA reaches the earth's surface, and because it is a known carcinogen, exposure to the sun should be restricted and accompanied by the use of sunscreens. UVC and the higher frequency range of UVB (found within the range of ionizing radiation) are almost totally absorbed in the ionosphere (the uppermost layer of the atmosphere) and therefore do not reach the earth's surface.
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Range of non-ionizing radiation in the electromagnetic spectrum |
The ionizing radiation spectrum
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High Ultraviolet range (UVB and UVC)
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X-ray range (or Rőntgen rays) named after Wilhelm Conrad Rőntgen
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Gamma (Ɣ) ray range.This type of radiation arises from disintegration of radioactive materials
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Range of ionizing radiation in the electromagnetic spectrum |
As noted above, some of the frequency ranges are further divided into sub-ranges. The International Telecommunications Union (ITU) has divided the radiofrequency range into wave bands. Examples of the uses of the radio frequency bands can be found at the link to the Table of Uses of Frequencies, based on the Table of Band Frequencies of the ITU.
References
- Finkenthal D, Greco B, Halsey R, Pena L, Rodecker S, Simms B. Introduction to the Electromagnetic Spectrum, (Editor Finkenthal Daniel), General Atomics, Fusion Education. Available at http://www.pa.uky.edu/~straley/EnergyOnline/Energy10/EnergyCourse/EMcurriculum.pdf. Last accessed 6 May 2015
- Hill WT III. Electromagnetic Radiation in: Encyclopedia of Applied Spectroscopy. (ed. Andrews DL) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
06.10.15
