spectrum
American Heritage Dictionary:
Top
spec·trum
(spĕk'trəm) 
n., pl., -tra (-trə), or -trums.
n., pl., -tra (-trə), or -trums.
- Physics. The distribution of a characteristic of a physical system or phenomenon, especially:
- The distribution of energy emitted by a radiant source, as by an incandescent body, arranged in order of wavelengths.
- The distribution of atomic or subatomic particles in a system, as in a magnetically resolved molecular beam, arranged in order of masses.
- A graphic or photographic representation of such a distribution.
- A range of values of a quantity or set of related quantities.
- A broad sequence or range of related qualities, ideas, or activities: the whole spectrum of 20th-century thought.
[Latin, appearance, from specere, to look at.]
Related Videos:
Top
spectrum
Fowler's Modern English Usage:
Top
spectrum
has the plural form spectra.
| spectre, spectator, specious, spurious | |
| speculator, speed verb., spell verb. |
Britannica Concise Encyclopedia:
Top
spectrum
Arrangement according to wavelength (or frequency) of electromagnetic radiation. The visible, rainbow spectrum is the portion of the electromagnetic spectrum that is visible as light to the human eye. Some sources emit only certain wavelengths and produce an emission spectrum of bright lines with dark spaces between. Such line spectra are characteristic of the elements that emit the radiation. A band spectrum consists of groups of wavelengths so close together that the lines appear to form a continuous band. Atoms and molecules absorb certain wavelengths and so remove them from a complete spectrum; the resulting absorption spectrum contains dark lines or bands at these wavelengths.
For more information on spectrum, visit Britannica.com.
Top
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 also Mass spectroscope; 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 also Atomic structure and spectra; Band spectrum; Electromagnetic radiation; Line spectrum; Molecular structure and spectra; Spectroscopy.
Computer Desktop Encyclopedia:
Top
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 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
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 Web site at
 |
 |
Download Computer Desktop Encyclopedia to your PC, iPhone or Android.
Barron's Marketing Dictionary:
Top
spectrum
Range of radiant energy (light) wavelengths. Within the visible spectrum, various light wavelengths are perceived as colors ranging from red to blue, depending upon the length of the wave. White light is a combination of all visible colors mixed in equal proportions. This characteristic of light, which enables it to be combined, so that the resultant light is equal to the sum of its constituent wavelengths, is called additive color mixing. See also cold color; subtractive primaries; warm color.
Columbia Encyclopedia:
Top
spectrum
spectrum, arrangement or display of light or other form of radiation separated according to wavelength, frequency, energy, or some other property. Beams of charged particles can be separated into a spectrum according to mass in a mass spectrometer (see mass spectrograph). Physicists often find it useful to separate a beam of particles into a spectrum according to their energy.
Continuous and Line Spectra
Dispersion, the separation of visible light into a spectrum, may be accomplished by means of a prism or a diffraction grating. Each different wavelength or frequency of visible light corresponds to a different color, so that the spectrum appears as a band of colors ranging from violet at the short-wavelength (high-frequency) end of the spectrum through indigo, blue, green, yellow, and orange, to red at the long-wavelength (low-frequency) end of the spectrum. In addition to visible light, other types of electromagnetic radiation may be spread into a spectrum according to frequency or wavelength.
The spectrum formed from white light contains all colors, or frequencies, and is known as a continuous spectrum. Continuous spectra are produced by all incandescent solids and liquids and by gases under high pressure. A gas under low pressure does not produce a continuous spectrum but instead produces a line spectrum, i.e., one composed of individual lines at specific frequencies characteristic of the gas, rather than a continuous band of all frequencies. If the gas is made incandescent by heat or an electric discharge, the resulting spectrum is a bright-line, or emission, spectrum, consisting of a series of bright lines against a dark background. A dark-line, or absorption, spectrum is the reverse of a bright-line spectrum; it is produced when white light containing all frequencies passes through a gas not hot enough to be incandescent. It consists of a series of dark lines superimposed on a continuous spectrum, each line corresponding to a frequency where a bright line would appear if the gas were incandescent. The Fraunhofer lines appearing in the spectrum of the sun are an example of a dark-line spectrum; they are caused by the absorption of certain frequencies of light by the cooler, outer layers of the solar atmosphere. Line spectra of either type are useful in chemical analysis, since they reveal the presence of particular elements. The instrument used for studying line spectra is the spectroscope.
The Quantum Explanation of Spectral Lines
The explanation for exact spectral lines for each substance was provided by the quantum theory. In his 1913 model of the hydrogen atom Niels Bohr showed that the observed series of lines could be explained by assuming that electrons are restricted to atomic orbits in which their orbital angular momentum is an integral multiple of the quantity h/2π, where h is Planck's constant. The integer multiple (e.g., 1, 2, 3 …) of h/2π is usually called the quantum number and represented by the symbol n.
When an electron changes from an orbit of higher energy (higher angular momentum) to one of lower energy, a photon of light energy is emitted whose frequency ν is related to the energy difference ΔE by the equation ν=ΔE/h. For hydrogen, the frequencies of the spectral lines are given by ν=cR (1/nf2−1/ni2) where c is the speed of light, R is the Rydberg constant, and nf and ni are the final and initial quantum numbers of the electron orbits (ni is always greater than nf). The series of spectral lines for which nf=1 is known as the Lyman series; that for nf=2 is the Balmer series; that for nf=3 is the Paschen series; that for nf=4 is the Brackett series; and that for nf=5 is the Pfund series. The Bohr theory was not as successful in explaining the spectra of other substances, but later developments of the quantum theory showed that all aspects of atomic and molecular spectra can be explained quantitatively in terms of energy transitions between different allowed quantum states.
Top
The range of wavelengths characteristic of a specific type of radiation.
Top
the plural of spectrum.
| spectinomycin, specificity constant, specificity | |
| spectrin, spectrofluorometer, spectrogram |
Random House Word Menu:
Top
categories related to 'spectrum'
- Optics - spectrum: array of various wavelengths that compose light
- Celestial Phenomena and Points - spectrum: light emitted by star or other source, dispersed according to wavelength
- Painting Tools and Techniques - spectrum: series of colored bands arranged in order of respective wavelength from infrared to ultraviolet
- Order, Hierarchy, and Systems - spectrum: continuous sequence or range
See crossword solutions for the clue Wikipedia on Answers.com:
Top
Spectrum
This article deals with the general meaning of "spectrum" and the history of its use. For other meanings and specific uses, see Spectrum (disambiguation).
A spectrum (plural spectra or spectrums[1]) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by analogy to many fields other than optics. Thus, one might talk about the spectrum of political opinion, or the spectrum of activity of a drug, or the autism spectrum. In these uses, values within a spectrum may not be associated with precisely quantifiable numbers or definitions. Such uses imply a broad range of conditions or behaviors grouped together and studied under a single title for ease of discussion.
In most modern usages of spectrum there is a unifying theme between extremes at either end. Some older usages of the word did not have a unifying theme, but they led to modern ones through a sequence of events set out below. Modern usages in mathematics did evolve from a unifying theme, but this may be difficult to recognize.
|
Contents
|
Origins
In Latin spectrum means "image" or "apparition", including the meaning "spectre". Spectral evidence is testimony about what was done by spectres of persons not present physically, or hearsay evidence about what ghosts or apparitions of Satan said. It was used to convict a number of persons of witchcraft at Salem, Massachusetts in the late 17th century. The word "spectrum" [Spektrum] was strictly used to designate a ghostly optical afterimage by Goethe in his Theory of Colors and Schopenhauer in On Vision and Colors.
Modern meaning in the physical sciences
In the 17th century the word spectrum was introduced into optics, referring to the range of colors observed when white light was dispersed through a prism. Soon the term referred to a plot of light intensity or power as a function of frequency or wavelength, also known as a spectral density.
The term spectrum was expanded to apply to other waves, such as sound waves that could also be measured as a function of frequency. The term now applies to any signal that can be measured or decomposed along a continuous variable such as energy in electron spectroscopy or mass to charge ratio in mass spectrometry. Spectrum is also used to refer to a graphical representation of the as a function of the dependent variable.
See also
 |
Wikimedia Commons has media related to: Spectrum |
Physical science
- Electromagnetic spectrum
- Visible spectrum or optical spectrum, a subset of the electromagnetic spectrum
- Emission spectrum observed in light
- Absorption spectrum observed in light
- Energy spectrum of a collection of particles (particle physics)
- Frequency spectrum of a signal
- Mass spectrum chemical analysis of atoms and molecules
- Power spectrum of a signal
- Radio spectrum
- Spectrogram
- Spectrometer
Social and medical sciences
- Antibiotic classification
- Economic spectrum
- Political spectrum of opinion
- Spectrum disorder, in psychiatry
Mathematics
- Spectrum (homotopy theory)
- Spectrum of a matrix, in linear algebra
- Spectrum of an operator, in functional analysis (a generalisation of the spectrum of a matrix)
- Spectrum of a ring, in commutative algebra
- Spectrum of a C*-algebra
- Spectrum of a theory, in mathematical logic
- Stone space of Boolean algebra
References
- ^ Dictionary.com. The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. (accessed: January 25, 2008).
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
Top
Spectrum
Français (French)
n. - (Phys) spectre, gamme
Deutsch (German)
n. - Spektrum
Ελληνική (Greek)
n. - (χρωματικό) φάσμα, μετείκασμα, (φυσ.) ηλιακό φάσμα, γκάμα
Português (Portuguese)
n. - espectro (m)
Русский (Russian)
спектр, диапазон, разнообразие, широкий диапазон, изображение, призрак, образ
Español (Spanish)
n. - gama, espectro
Svenska (Swedish)
n. - spektrum, skala
中文（简体）(Chinese (Simplified))
谱, 频谱, 光谱, 射频频谱
中文（繁體）(Chinese (Traditional))
n. - 譜, 頻譜, 光譜, 射頻頻譜
한국어 (Korean)
n. - 스펙트럼, 잔상, 분포 범위
日本語 (Japanese)
n. - スペクトル, 分光, 残像, 範囲, 周波数域
العربيه (Arabic)
(الاسم) الطيف ( الضوئي)
עברית (Hebrew)
n. - תחזית, ספקטרום, צבעי הקשת, טווח כולל של דרגות מסווגות
If you are unable to view some languages clearly, click here.
Post a question - any question - to the WikiAnswers community:
Copyrights:
American Heritage Dictionary
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
Read more
Britannica Concise Encyclopedia
Britannica Concise Encyclopedia. © 1994-2012 Encyclopædia Britannica, Inc. All rights reserved. Read more
McGraw-Hill Science & Technology Encyclopedia
McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.
Read more
Computer Desktop Encyclopedia
THIS DEFINITION IS FOR PERSONAL USE ONLY.
All other reproduction is strictly prohibited without permission from the publisher.
© 1981-2012 The Computer Language Company Inc. All rights reserved. Read more
All other reproduction is strictly prohibited without permission from the publisher.
© 1981-2012 The Computer Language Company Inc. All rights reserved. Read more
Barron's Marketing Dictionary
Dictionary of Marketing Terms. Copyright © 2000 by Barron's Educational Series, Inc. All rights reserved.
Read more
Columbia Encyclopedia
The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2012, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/.
Read more
Dictionary of Cultural Literacy: Science
The New Dictionary of Cultural Literacy, Third Edition Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin. All rights reserved.
Read more
Oxford Dictionary of Biochemistry
Oxford University Press. Oxford Dictionary of Biochemistry and Molecular Biology © 1997, 2000, 2006 All rights reserved.
Read more
Random House Word Menu
© 2010 Write Brothers Inc. Word Menu is a registered trademark of the Estate of Stephen Glazier.
Write Brothers Inc.
All rights reserved.
Read more
Bradford's Crossword Solver's Dictionary
Collins Bradford's Crossword Solver's Dictionary © Anne Bradford, 1986, 1993, 1997, 2000, 2003, 2005, 2008
HarperCollins Publishers
All rights reserved.
Read more
Wikipedia on Answers.com
This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article Spectrum.
Read more
