Editing Resonance (section)

== Q factor==
{{Main|Q factor}}
[[File:High and low Q factor.svg|thumb|High and low Q factor]]
The ''Q'' factor or ''quality factor'' is a [[Dimensionless quantity|dimensionless]] parameter that describes how under-damped an [[oscillation|oscillator]] or resonator is, and characterizes the [[bandwidth (signal processing)|bandwidth]] of a resonator relative to its center frequency.{{sfn|Harlow|2004|p=2.216}}{{sfn|Tooley|2006|pp=77&ndash;78}}
A high value for ''Q'' indicates a lower rate of energy loss relative to the stored energy, i.e., the system is lightly damped. The parameter is defined by the equation:
<math display="block"> Q =2\pi \text{ } \frac{ \text{ maximum energy stored}}{ \text{total energy lost per cycle at resonance}} </math>.<ref name="MIT">{{cite web |title=Frequency response: Resonance, Bandwidth, Q factor |url=https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-071j-introduction-to-electronics-signals-and-measurement-spring-2006/lecture-notes/resonance_qfactr.pdf | archive-url = https://ghostarchive.org/archive/20221009/https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-071j-introduction-to-electronics-signals-and-measurement-spring-2006/lecture-notes/resonance_qfactr.pdf |archive-date=2022-10-09 |url-status=live |publisher=[[Massachusetts Institute of Technology]] |access-date=3 January 2021}}</ref>

The higher the Q factor, the greater the amplitude at the resonant frequency, and the smaller the ''bandwidth'', or range of frequencies around resonance occurs. In electrical resonance, a high-''Q'' circuit in a radio receiver is more difficult to tune, but has greater [[selectivity (radio)|selectivity]], and so would be better at filtering out signals from other stations. High Q oscillators are more stable.<ref name="MIT" />

Examples that normally have a low Q factor include [[door closer]]s (Q=0.5). Systems with high Q factors include  [[tuning fork]]s (Q=1000), [[atomic clock]]s and lasers (Q≈10<sup>11</sup>).<ref name="NIST">{{cite journal |last1=Physical Measurement Laboratory |title=Time and Frequency from A to Z, Q to Ra |url=https://www.nist.gov/pml/time-and-frequency-division/popular-links/time-frequency-z/time-and-frequency-z-q-ra |journal=NIST |date=12 May 2010 |publisher=[[National Institute of Standards and Technology]] (NIST) |access-date=1 January 2021}}</ref>