Editing Q factor (section)

{{Short description|Parameter describing the longevity of energy in a resonator relative to its resonant frequency}}
{{For|other uses of the terms '''Q''', '''Q factor''', and '''Quality factor'''|Q value (disambiguation)}}
{{DISPLAYTITLE:''Q'' factor}}
[[File:Damped oscillation function plot.svg|thumb|upright=1.5| A damped oscillation.  A low {{mvar|Q}} factor – about 5 here – means the oscillation dies out rapidly.]]
In [[physics]] and [[engineering]], the '''quality factor''' or '''{{mvar|Q}} factor''' is a [[Dimensionless quantity|dimensionless]] parameter that describes how [[underdamped]] an [[oscillator]] or [[resonator]] is.  It is defined as the ratio of the initial energy stored in the resonator to the energy lost in one [[radian]] of the cycle of oscillation.<ref>{{cite book |last1=Hickman |first1=Ian |title=Analog Electronics: Analog Circuitry Explained |date=2013 |publisher=Newnes |page=42 |url=https://books.google.com/books?id=l-AgBQAAQBAJ&pg=PA42 | isbn= 9781483162287}}</ref> {{mvar|Q}} factor is alternatively defined as the ratio of a resonator's centre frequency to its [[bandwidth (signal processing)|bandwidth]] when subject to an oscillating driving force.  These two definitions give numerically similar, but not identical, results.<ref>{{cite book
 |title       = Electronic circuits: fundamentals and applications
 |first       = Michael H.
 |last        = Tooley
 |publisher   = Newnes
 |year        = 2006
 |isbn        = 978-0-7506-6923-8
 |pages       = 77–78
 |url         = https://books.google.com/books?id=rwWWvtQYEO0C&pg=PA78
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20161201212653/https://books.google.com/books?id=8fuppV9O7xwC&pg=PA77&dq=q-factor+bandwidth#v=onepage&q=q-factor%20bandwidth&f=false
 |archive-date = 2016-12-01
}}</ref> Higher {{mvar|Q}} indicates a lower rate of energy loss and the oscillations die out more slowly. A pendulum suspended from a high-quality bearing, oscillating in air, has a high {{mvar|Q}}, while a pendulum immersed in oil has a low one. Resonators with high quality factors have low [[Damping ratio|damping]], so that they ring or vibrate longer.