spectrum

spectrum

1. the distribution of colours produced when white light is dispersed by a prism or diffraction grating. There is a continuous change in wavelength from red, the longest wavelength, to violet, the shortest. Seven colours are usually distinguished: violet, indigo, blue, green, yellow, orange, and red

2. the whole range of electromagnetic radiation with respect to its wavelength or frequency

3. any particular distribution of electromagnetic radiation often showing lines or bands characteristic of the substance emitting the radiation or absorbing it

4. any similar distribution or record of the energies, velocities, masses, etc., of atoms, ions, electrons, etc.

5. another name for an afterimage

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

Spectrum

The term spectrum is applied to any class of similar entities or properties strictly arrayed in order of increasing or decreasing magnitude. In general, a spectrum is a display or plot of intensity of radiation (particles, photons, or acoustic radiation) as a function of mass, momentum, wavelength, frequency, or some other related quantity. For example, a β-ray spectrum represents the distribution in energy or momentum of negative electrons emitted spontaneously by certain radioactive nuclides, and when radionuclides emit α-particles, they produce an α-particle spectrum of one or more characteristic energies. A mass spectrum is produced when charged particles (ionized atoms or molecules) are passed through a mass spectrograph in which electric and magnetic fields deflect the particles according to their charge-to-mass ratios. The distribution of sound-wave energy over a given range of frequencies is also called a spectrum. See Sound

In the domain of electromagnetic radiation, a spectrum is a series of radiant energies arranged in order of wavelength or of frequency. The entire range of frequencies is subdivided into wide intervals in which the waves have some common characteristic of generation or detection, such as the radio-frequency spectrum, infrared spectrum, visible spectrum, ultraviolet spectrum, and x-ray spectrum.

Spectra are also classified according to their origin or mechanism of excitation, as emission, absorption, continuous, line, and band spectra. An emission spectrum is produced whenever the radiations from an excited light source are dispersed. An absorption spectrum is produced against a background of continuous radiation by interposing matter that reduces the intensity of radiation at certain wavelengths or spectral regions. The energies removed from the continuous spectrum by the interposed absorbing medium are precisely those that would be emitted by the medium if properly excited. A continuous spectrum contains an unbroken sequence of waves or frequencies over a long range. Line spectra are discontinuous spectra characteristic of excited atoms and ions, whereas band spectra are characteristic of molecular gases or chemical compounds. See Atomic structure and spectra, Electromagnetic radiation, Line spectrum, Molecular structure and spectra, Spectroscopy

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

spectrum

(spek -trŭm) A display or record of the distribution of intensity of electromagnetic radiation with wavelength or frequency. Thus, the spectrum of a celestial body is obtained by dispersing that radiation from it into its constituent wavelengths so that the wavelengths present and their intensities can be observed. A variety of techniques exist for obtaining spectra, depending on the part of the electromagnetic spectrum studied. The result may be a photographic record (as can be obtained in a spectrograph) or a plot of intensity against wavelength or frequency (as can be produced by electronic and associated equipment).

The spectrum of a particular source of electromagnetic radiation depends on the processes producing emission of radiation (see emission spectrum) and/or on the way in which radiation is absorbed by intermediate material (see absorption spectrum). Spectra are also classified by their appearance. A line spectrum has discrete lines caused by emission or absorption of radiation at fixed wavelengths. A band spectrum has distinctive bands of absorption or emission. A continuous spectrum occurs when continuous emission or absorption takes place over a wide range of wavelengths. See also spectroscopy.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

spectrum

[′spek·trəm]

(mathematics)

If T is a linear operator of a normed space X to itself and I is the identity transformation (I (x) ≡ x), the spectrum of T consists of all scalars λ for which either T- λ I has no inverse or the range of T- λ I is not dense in X.

(physics)

A display or plot of intensity of radiation (particles, photons, or acoustic radiation) as a function of mass, momentum, wavelength, frequency, or some related quantity.

The set of frequencies, wavelengths, or related quantities, involved in some process; for example, each element has a characteristic discrete spectrum for emission and absorption of light.

A range of frequencies within which radiation has some specified characteristic, such as audio-frequency spectrum, ultraviolet spectrum, or radio spectrum.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Spectrum

ZX Spectrum

This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

spectrum

The range of electromagnetic radiation (electromagnetic waves) in our known universe, which includes visible light. The radio spectrum, which includes both licensed and unlicensed frequencies up to 300 GHz has been defined worldwide in three regions: Europe and Northern Asia (Region 1); North and South America (Region 2), and Southern Asia and Australia (Region 3). Some frequency bands are used for the same purpose in all three regions while others differ. See satellite frequency bands and optical bands.

Higher Frequencies
Frequencies above 40 GHz have not been licensed, but are expected to be made available in the future as the technology is developed to transmit at these smaller wavelengths (higher frequencies). The spectrum can be viewed in meticulous detail from the Federal Communications Commission (FCC) and National Telecommunications and Information Administration (NTIA) by visiting www.fcc.gov/oet/spectrum and www.ntia.doc.gov/osmhome/osmhome.html. See electromagnetic radiation and wave.

Should Airwaves Be Licensed?

There is a great deal of controversy over the licensing of frequencies. In Kevin Werbach's very educational white paper, "Radio Revolution," the author says an artificial scarcity has been created because policy makers do not understand the technology. He states that many believe the traditional policy of dividing the airwaves into licensed bands now impedes progress because today's radio technologies allow for much more sharing of the spectrum than ever before. The old notion that radio waves interfere with and cancel each other is a false one. Waves just mix together and become more difficult to differentiate, but modern electronics can, in fact, separate them.

To obtain a copy of this insightful report written in 2003, as well as other related articles, visit Werbach's website at www.werbach.com. See smart radio.

Visible Light

Our eyes perceive a tiny sliver of the electromagnetic spectrum. The wavelengths from (approximately) 400 to 750 nanometers provide us with our physical view of the universe.

Visible Light

Our eyes perceive a tiny sliver of the electromagnetic spectrum. The wavelengths from (approximately) 400 to 750 nanometers provide us with our physical view of the universe.

Copyright © 1981-2025 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Spectrum

 

in physics, the set of different values that a given physical quantity can take on. Spectra can be continuous or discrete (discontinuous). The concept of a spectrum is applied most often to oscillatory processes. We speak, for example, of oscillation spectra, sound spectra, and optical spectra. In nuclear physics, such concepts as mass spectra, momentum spectra, and energy spectra are used.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.