Editing Frequency (section)

== Examples ==

=== Light ===
{{main article|Light|Electromagnetic radiation}}
<!--Linked from [[Neil Harbisson]]-->
[[File:EM spectrum.svg|thumb|upright=2|Complete spectrum of [[electromagnetic radiation]] with the visible portion highlighted]]

Visible light is an [[electromagnetic wave]], consisting of oscillating [[electric field|electric]] and [[magnetic field]]s traveling through space. The frequency of the wave determines its color: 400 THz ({{val|4|e=14|ul=}} Hz) is red light, 800 THz ({{val|8|e=14|u=Hz}}) is violet light, and between these (in the range 400–800 THz) are all the other colors of the [[visible spectrum]]. An electromagnetic wave with a frequency less than {{val|4|e=14|u=Hz}} will be invisible to the human eye; such waves are called [[infrared]] (IR) radiation. At even lower frequency, the wave is called a [[microwave]], and at still lower frequencies it is called a [[radio wave]]. Likewise, an electromagnetic wave with a frequency higher than {{val|8|e=14|u=Hz}} will also be invisible to the human eye; such waves are called [[ultraviolet]] (UV) radiation. Even higher-frequency waves are called [[X-ray]]s, and higher still are [[gamma ray]]s.

All of these waves, from the lowest-frequency radio waves to the highest-frequency gamma rays, are fundamentally the same, and they are all called [[electromagnetic radiation]]. They all travel through vacuum at the same speed (the speed of light), giving them wavelengths inversely proportional to their frequencies.
<math display=block qid=Q2111>\displaystyle c=f\lambda,</math>
where ''c'' is the speed of light (''c'' in vacuum or less in other media), ''f'' is the frequency and ''λ'' is the wavelength.

In [[Dispersion (optics)|dispersive media]], such as glass, the speed depends somewhat on frequency, so the wavelength is not quite inversely proportional to frequency.

=== Sound ===
{{main article|Audio frequency}}
[[File:Ultrasound range diagram.svg|thumb|upright=1.7|The [[sound wave]] spectrum, with rough guide of some applications]]

Sound propagates as mechanical vibration waves of pressure and displacement, in air or other substances.<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/sound|title=Definition of SOUND|access-date=3 October 2016}}</ref> In general, frequency components of a sound determine its "color", its [[timbre]]. When speaking about the frequency (in singular) of a sound, it means the property that most determines its [[Pitch (music)|pitch]].<ref>{{Cite book|last1= Pilhofer |first1=Michael |title=Music Theory for Dummies|url=https://books.google.com/books?id=CxcviUw4KX8C|year=2007|publisher=For Dummies|page=97|isbn= 978-0-470-16794-6}}</ref>

The frequencies an ear can hear are limited to a [[threshold of hearing|specific range of frequencies]].  The [[audible frequency]] range for humans is typically given as being between about 20&nbsp;Hz and 20,000&nbsp;Hz (20&nbsp;kHz), though the high frequency limit usually reduces with age. Other [[species]] have different hearing ranges. For example, some dog breeds can perceive vibrations up to 60,000&nbsp;Hz.<ref name="Physics Factbook">
{{cite web
| url=https://hypertextbook.com/facts/2003/TimCondon.shtml
| title=Frequency range of dog hearing
| first=Tim
| last=Condon
| year=2003
| website=The Physics Factbook
| editor-last=Elert
| editor-first=Glenn
| accessdate=2008-10-22
}}</ref>

In many media, such as air, the [[speed of sound]] is approximately independent of frequency, so the wavelength of the sound waves (distance between repetitions) is approximately inversely proportional to frequency.

=== Line current ===
{{main article|Utility frequency}}
In [[Europe]], [[Africa]], [[Australia]], southern [[South America]], most of [[Asia]], and [[Russia]], the frequency of the [[alternating current]] in [[mains electricity|household electrical outlets]] is 50&nbsp;Hz (close to the [[Musical note|tone]] G), whereas in [[North America]] and northern South America, the frequency of the alternating current in household electrical outlets is 60&nbsp;Hz (between the tones B{{music|♭}} and B; that is, a [[minor third]] above the European frequency). The frequency of the '[[mains hum|hum]]' in an [[audio recording]] can show in which of these general regions the recording was made.