electromagnetic radiation (redirected from Radiation emissions)

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

Energy propagated through free space or through a material medium in the form of electromagnetic waves. Examples include radio waves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays. Electromagnetic radiation exhibits wavelike properties such as reflection, refraction, diffraction, and interference, but also exhibits particlelike properties in that its energy occurs in discrete packets, or quanta. Though all types of electromagnetic radiation travel at the same speed, they vary in frequency and wavelength, and interact with matter differently. A vacuum is the only perfectly transparent medium; all others absorb some frequencies of electromagnetic radiation.

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electromagnetic radiation

The energy that radiates from all things in nature and from man-made electronic systems. It includes cosmic rays, gamma rays, x-rays, ultraviolet light, visible light, infrared light, radar, microwaves, TV, radio, cellphones and all electronic transmission systems. Electromagnetic radiation is made up of electric and magnetic fields that move at right angles to each other at the speed of light. See spectrum.

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electromagnetic radiation [i¦lek·trō·mag′ned·ik ‚rād·ē′ā·shən]

(electromagnetism)

Electromagnetic waves and, especially, the associated electromagnetic energy.

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Electromagnetic radiation

Energy transmitted through space or through a material medium in the form of electromagnetic waves. The term can also refer to the emission and propagation of such energy. Whenever an electric charge oscillates or is accelerated, a disturbance characterized by the existence of electric and magnetic fields propagates outward from it. This disturbance is called an electromagnetic wave. The frequency range of such waves is tremendous, as is shown by the electromagnetic spectrum in the table. The sources given are typical, but not mutually exclusive.

In theory, any electromagnetic radiation can be detected by its heating effect. This method has actually been used over the range from x-rays to radio. lonization effects measured by cloud chambers, photographic emulsions, ionization chambers, and Geiger counters have been used in the γ- and x-ray regions. Direct photography can be used from the γ-ray to the infrared region.

Electromagnetic spectrum

Frequency,	Wavelength,
Hz	m	Nomenclature	Typical source
1023	3 × 10-15	Cosmic photons	Astronomical
1022	3 × 10-14	γ-rays	Radioactive nuclei
1021	3 × 10-13	γ-rays, x-rays
1020	3 × 10-12	x-rays	Atomic inner shell
		Positron-electron annihilation
1019	3 × 10-11	Soft x-rays	Electron impact on a solid
1018	3 × 10-10	Ultraviolet, x-rays	Atoms in sparks
1017	3 × 10-9	Ultraviolet	Atoms in sparks and arcs
1016	3 × 10-8	Ultraviolet	Atoms in sparks and arcs
1015	3 × 10-7	Visible spectrum	Atoms, hot bodies,
			molecules
1014	3 × 10-6	Infrared	Hot bodies, molecules
1013	3 × 10-5	Infrared	Hot bodies, molecules
1012	3 × 10-4	Far-infrared	Hot bodies, molecules
1011	3 × 10-3	Microwaves	Electronic devices
1010	3 × 10-2	Microwaves, radar	Electronic devices
109	3 × 10-1	Radar	Electronic devices
		Interstellar hydrogen
108	3	Television, FM radio	Electronic devices
107	30	Short-wave radio	Electronic devices
106	300	AM radio	Electronic devices
105	3000	Long-wave radio	Electronic devices
104	3 × 104	Induction heating	Electronic devices
103	3 × 105		Electronic devices
100	3 × 106	Power	Rotating machinery
10	3 × 107	Power	Rotating machinery
1	3 × 108		Commutated direct current
0	Infinity	Direct current	Batteries

Fluorescence is effective in the x-ray and ultraviolet ranges. Bolometers, thermocouples, and other heat-measuring devices are used chiefly in the infrared and microwave regions. Crystal detectors, vacuum tubes, and transistors cover the microwave and radio frequency ranges. See Diffraction, Electromagnetic wave, Gamma rays, Heat radiation, Infrared radiation, Interference of waves, Light, Maxwell's equations, Polarization of waves, Reflection of electromagnetic radiation, Refraction of waves, Scattering of electromagnetic radiation, Ultraviolet radiation, Wave motion, X-rays