Editing Q factor (section)

==Explanation==
The {{mvar|Q}} factor is a parameter that describes the [[resonance]] behavior of an underdamped [[harmonic oscillator]] (resonator). [[sine wave|Sinusoidally]] driven [[resonator]]s having higher {{mvar|Q}} factors [[resonance|resonate]] with greater amplitudes (at the resonant frequency) but have a smaller range of frequencies around that frequency for which they resonate; the range of frequencies for which the oscillator resonates is called the bandwidth. Thus, a high-{{mvar|Q}} [[RLC circuit|tuned circuit]] in a radio receiver would be more difficult to tune, but would have more [[selectivity (radio)|selectivity]]; it would do a better job of filtering out signals from other stations that lie nearby on the spectrum. High-{{mvar|Q}} oscillators [[oscillator phase noise|oscillate with a smaller range of frequencies]] and are more stable.

The quality factor of oscillators varies substantially from system to system, depending on their construction. Systems for which damping is important (such as dampers keeping a door from slamming shut) have {{mvar|Q}} near {{1/2}}. Clocks, lasers, and other resonating systems that need either strong resonance or high frequency stability have high quality factors. Tuning forks have quality factors around 1000. The quality factor of [[atomic clock]]s, [[Superconducting Radio Frequency|superconducting RF]] cavities used in accelerators, and some high-{{mvar|Q}} [[optical cavity|lasers]] can reach as high as 10<sup>11</sup><ref>

[http://www.rp-photonics.com/q_factor.html Encyclopedia of Laser Physics and Technology: ''Q'' factor] {{webarchive
 | url=https://web.archive.org/web/20090224211703/http://www.rp-photonics.com/q_factor.html
 | date=2009-02-24
}}</ref> and higher.<ref>

[http://tf.nist.gov/general/enc-q.htm Time and Frequency from A to Z: Q to Ra] {{webarchive
 | url=https://web.archive.org/web/20080504160852/http://tf.nist.gov/general/enc-q.htm
 | date=2008-05-04
}}</ref>

There are many alternative quantities used by physicists and engineers to describe how damped an oscillator is. Important examples include: the [[damping ratio]], [[bandwidth (signal processing)|relative bandwidth]], [[oscillator linewidth|linewidth]] and bandwidth measured in [[Octave (electronics)|octave]]s.

The concept of {{mvar|Q}} originated with K. S. Johnson of [[Western Electric Company]]'s Engineering Department while evaluating the quality of coils (inductors). His choice of the symbol {{mvar|Q}} was only because, at the time, all other letters of the alphabet were taken. The term was not intended as an abbreviation for "quality" or "quality factor", although these terms have grown to be associated with it.<ref name="Green">
{{Cite journal
 |last1=Green|first1=Estill I.
 |date=October 1955
 |title=The Story of Q
 |url=http://www.collinsaudio.com/Prosound_Workshop/The_story_of_Q.pdf
 |journal=[[American Scientist]]
 |volume=43|pages=584–594
 |archive-url=https://web.archive.org/web/20121203044200/http://www.collinsaudio.com/Prosound_Workshop/The_story_of_Q.pdf
 |archive-date=2012-12-03
 |access-date=2012-11-21
 |url-status=live
}}</ref><ref>B. Jeffreys, Q.Jl R. astr. Soc. (1985) 26, 51–52</ref><ref name="Paschotta">{{cite book
 |last        = Paschotta
 |first       = Rüdiger
 |title       = Encyclopedia of Laser Physics and Technology, Vol. 1: A-M
 |publisher   = Wiley-VCH
 |year        = 2008
 |pages       = 580
 |url         = https://books.google.com/books?id=hdkJ5ASTFjcC&q=%22Q+factor%22+definition+history&pg=PA580
 |isbn        = 978-3527408283
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20180511181437/https://books.google.com/books?id=hdkJ5ASTFjcC&pg=PA580&dq=%22Q+factor%22+definition+history
 |archive-date = 2018-05-11
}}</ref>