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electromagnetic radiation
electromagnetic radiation energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic field, and if the motion is changing (accelerated), then the magnetic field varies and in turn produces an electric field. These interacting electric and magnetic fields are at right angles to one another and also to the direction of propagation of the energy. Thus, an electromagnetic wave is a transverse wave. If the direction of the electric field is constant, the wave is said to be polarized (see polarization of light ). Electromagnetic radiation does not require a material medium and can travel through a vacuum. The theory of electromagnetic radiation was developed by James Clerk Maxwell and published in 1865. He showed that the speed of propagation of electromagnetic radiation should be identical with that of light , about 186,000 mi (300,000 km) per sec. Subsequent experiments by Heinrich Hertz verified Maxwell's prediction through the discovery of radio waves, also known as hertzian waves. Light is a type of electromagnetic radiation, occupying only a small portion of the possible spectrum of this energy. The various types of electromagnetic radiation differ only in wavelength and frequency; they are alike in all other respects. The possible sources of electromagnetic radiation are directly related to wavelength: long radio waves are produced by large antennas such as those used by broadcasting stations; much shorter visible light waves are produced by the motions of charges within atoms ; the shortest waves, those of gamma radiation , result from changes within the nucleus of the atom. In order of decreasing wavelength and increasing frequency, various types of electromagnetic radiation include: electric waves, radio waves (including AM, FM, TV, and shortwaves), microwaves, infrared radiation , visible light, ultraviolet radiation , X rays , and gamma radiation. According to the quantum theory , light and other forms of electromagnetic radiation may at times exhibit properties like those of particles in their interaction with matter. (Conversely, particles sometimes exhibit wavelike properties.) The individual quantum of electromagnetic radiation is known as the photon and is symbolized by the Greek letter gamma. Quantum effects are most pronounced for the higher frequencies, such as gamma rays, and are usually negligible for radio waves at the long-wavelength, low-frequency end of the spectrum. |
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"electromagnetic radiation." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "electromagnetic radiation." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1E1-electrom-r.html "electromagnetic radiation." The Columbia Encyclopedia, 6th ed.. 2008. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-electrom-r.html |
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electromagnetic radiation
electromagnetic radiation Energy arising from the acceleration of electrically charged entities (e.g. electrons). Electromagnetic radiation can be considered to be composed of waves or particles, since it displays properties of both; this is referred to as the wave–particle duality. Electromagnetic waves are composed of oscillating electric and magnetic fields which lie at right angles to each other and to the direction of travel. They propagate through a vacuum at the speed of light, c; the speed is slower when travelling through a medium such as air, water, or glass. The waves have a wavelength, λ, and a frequency, f or ν, which are linked by the equation c = f λ. Electromagnetic radiation may also be regarded as being composed of a stream of particles of zero mass called photons. The energy, E, of a photon is related to frequency by Planck's formula E = hf, where h is the Planck constant. Hence the higher the frequency, the greater the energy of the radiation.
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"electromagnetic radiation." A Dictionary of Astronomy. 1997. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "electromagnetic radiation." A Dictionary of Astronomy. 1997. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O80-electromagneticradiation.html "electromagnetic radiation." A Dictionary of Astronomy. 1997. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-electromagneticradiation.html |
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electromagnetic radiation
electromagnetic radiation Energy in the form of transverse waves. It travels through free space at close to the speed of light, c.300,000km (186,000mi)/sec. In general, electromagnetic waves are set up by electrical and magnetic vibrations that occur universally in atoms. The wavelength of electromagnetic radiation varies inversely with the wave frequency. These waves make up the electromagnetic spectrum, which includes (in ascending order of frequency): radio waves (including microwaves), infrared waves, light, ultraviolet radiation, X-rays, and gamma radiation. They can undergo reflection, refraction, interference, diffraction, and polarization. In some cases, such as the photoelectric effect, electromagnetic radiation behaves in a way that can only be explained by assuming the radiation is composed of quanta of energy (photons). See also quantum theory
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"electromagnetic radiation." World Encyclopedia. 2005. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "electromagnetic radiation." World Encyclopedia. 2005. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O142-electromagneticradiation.html "electromagnetic radiation." World Encyclopedia. 2005. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-electromagneticradiation.html |
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electromagnetic radiation
electromagnetic radiation (EMR) The range in radiation extending from wavelengths of less than 10−12m to more than 103m. In order of increasing wavelength are included cosmic ray photons, gamma rays, X-rays, ultraviolet radiation, visible light (violet to red), infrared radiation, microwaves, radio waves, and electric currents.
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AILSA ALLABY and MICHAEL ALLABY. "electromagnetic radiation." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "electromagnetic radiation." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O13-electromagneticradiation.html AILSA ALLABY and MICHAEL ALLABY. "electromagnetic radiation." A Dictionary of Earth Sciences. 1999. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-electromagneticradiation.html |
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electromagnetic radiation
electromagnetic radiation radiation made up of oscillating electric and magnetic fields and propagated with the speed of light. Electromagnetic radiation includes gamma radiation, X rays, ultraviolet radiation, visible radiation, infrared radiation, radar, and radio waves.
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"electromagnetic radiation." The Oxford Essential Dictionary of the U.S. Military. 2001. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "electromagnetic radiation." The Oxford Essential Dictionary of the U.S. Military. 2001. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O63-electromagneticradiation.html "electromagnetic radiation." The Oxford Essential Dictionary of the U.S. Military. 2001. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O63-electromagneticradiation.html |
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