Spectrum: Wikis

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From Wikipedia, the free encyclopedia

The spectrum in a rainbow

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.

Modern meaning in the physical sciences

The spectrum of a star of spectral type K4III

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 soon applied to other waves, such as sound waves, and now applies to any signal that can be decomposed into frequency components. A spectrum is a usually 2-dimensional plot, of a compound signal, depicting the components by another measure. Sometimes, the word spectrum refers to the compound signal itself, such as the "spectrum of visible light", a reference to those electromagnetic waves which are visible to the human eye. Looking at light through a prism separates visible light into its colors according to wavelength. It separates them according to its dispersion relation and a grating separates according to the grating equation and if massive particles are measured often their speed is measured. To get a spectrum, the measured function has to be transformed in their independent variable to frequencies and the dependent variable has to be reduced in regions, where the independent variable is stretched. For this imagine that the spectrum of pulse with a finite number of particles is measured on a film or a CCD. Assuming no particles are lost, any nonlinearity (compared to frequency) on the spectral separation concentrates particles at some points of the film. The same is true for taking a spectrum by scanning a monochromator with a fixed slit width. Violet at one end has the shortest wavelength and red at the other end has the longest wavelength of visible light. The colors in order are violet, blue, green, yellow, orange, red. As the wavelengths get bigger below the red visible light they become infrared, microwave, and radio. As the wavelengths get smaller above violet light, they become ultra-violet, x-ray, and gamma ray.

See also

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Physical science

Social and medical sciences

Mathematics

References

  1. ^ Dictionary.com. The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. (accessed: January 25, 2008).

Strategy wiki

Up to date as of January 23, 2010
(Redirected to Category:Sinclair ZX Spectrum article)

From StrategyWiki, the free strategy guide and walkthrough wiki

This system category is a stub. Help us expand it with system details as well as a {{system}} infobox. Reliable information can be researched on Wikipedia or you can just search for "Sinclair ZX Spectrum" on Google. Do this and you get a cookie.

Sinclair ZX Spectrum
The console image for Sinclair ZX Spectrum.
Manufacturer Sinclair Research
Active 19821990
Total Games 432 (107 present)
← Sinclair ZX81 Sinclair QL →

The Sinclair ZX Spectrum was a home computer released in the United Kingdom by Sinclair Research in 1982. While originally called the "ZX82", the system was renamed the ZX Spectrum in order to promote its colour display. It proved immensely popular in various incarnations over the years and remains the most successful British computer ever made.

  • Spectrum 16K/48K: Released in 1982
  • Spectrum+: Released in 1984
  • Spectrum 128: Released in 1985
  • Spectrum +2/+2A: Released in 1987, 1988
  • Spectrum +3: Released in 1988

Pages in category "Sinclair ZX Spectrum"

The following 107 pages are in this category, out of 107 total.

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  • 007: Licence to Kill

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  • 1942
  • 1943: The Battle of Midway

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Simple English

This article is about the visible spectrum. For all other uses see: Spectrum (disambiguation)

File:Rainbow above Kaviskis Lake,
The spectrum in a rainbow

A spectrum (plural: spectra or spectrums[1]) is a band of several colours, violet, indigo, blue, green, yellow, orange and red. A spectrum can be seen if the Sun's light is passed through a prism and allowed to gather on a white screen.[2] A natural example of a spectrum is a rainbow. The word spectrum was first used by scientists studying optics. They used the word to describe the rainbow of colors in visible light when separated using a prism. The spectrum seen when light passes through a prism is an example of the dispersion of light. The material from which the prism is made has a different refractive index n than air. Usually, nprism is greater than nair, and nair is taken to be approximately one. This implies that light travels a little slower in the material of the prism than in the space surrounding it. The angle of refraction can be determined from the angle of incidence and the refractive indexes using Snell's law. The reason why the white light separates into in its component colors instead of remaining white is because the shorter wavelengths are refracted, or bent, more than the longer wavelengths. Thus, red, having the longest visible wavelength, will appear closest to the line perpendicular to the surface of the material (the normal), that is, it will be bent the least. Violet light, with the smallest wavelength in the visible spectrum, will be bent the most. The rainbow produced will always be in the same order: red, orange, yellow, green, blue, indigo, violet.

References


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