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{{StatsPsy}}
 
{{StatsPsy}}
 
{{PsyPerspective}}
 
{{PsyPerspective}}
[[Image:Sine waves different frequencies.svg|thumb|right|360px|[[Sine wave]]s of various frequencies; the bottom waves have higher frequencies than those above.]]
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[[Image:Sine waves different frequencies.svg|thumb|right|360px|Sine waves of various frequencies; the bottom waves have higher frequencies than those above.]]
'''Frequency''' is the [[measurement]] of the number of occurrences of a repeated event per unit of [[time]]. It is also defined as the rate of change of [[phase (waves)|phase]] of a [[sinusoid]]al waveform.
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'''Frequency''' is the [[measurement]] of the number of occurrences of a repeated event per unit of [[time]].
   
 
== Measurement ==
 
== Measurement ==
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</math>
 
</math>
   
In the [[special case]] of electromagnetic waves moving through a [[vacuum]], then '''v = c''', where '''c''' is the [[speed of light]] in a vacuum, and this expression becomes:
 
:<math>
 
f = \frac{c}{\lambda}
 
</math>
 
   
 
When [[waves]] travel from one [[Medium (optics)|medium]] to another, their frequency remains exactly the same &mdash; only their [[wavelength]] and [[speed]] change.
 
When [[waves]] travel from one [[Medium (optics)|medium]] to another, their frequency remains exactly the same &mdash; only their [[wavelength]] and [[speed]] change.
 
Apart from being modified by the [[Doppler effect]] or any other nonlinear process, frequency is an invariant quantity in the universe. That is, it cannot be changed by any linearly physical process unlike velocity of propagation or wavelength.
 
   
 
Frequency is also a measure of temperature, as for when the temperature of a molecule is increased it will vibrate faster. The faster the molecule will vibrate the higher the frequency.
 
Frequency is also a measure of temperature, as for when the temperature of a molecule is increased it will vibrate faster. The faster the molecule will vibrate the higher the frequency.
   
 
==Examples==
 
==Examples==
*The frequency of the standard pitch A above [[middle C]] is usually defined as [[A440|440 Hz]], that is, 440 cycles per second ({{Audio|Media-440Hz.ogg|Listen}}) and known as concert [[Pitch (music)|pitch]], to which an [[orchestra]] tunes.
+
*The frequency of the standard pitch A above [[middle C]] is usually defined as [[A440|440 Hz]], that is, 440 cycles per second ({{Audio|Media-440Hz.ogg|Listen}}) and known as concert [[Pitch (music)|pitch]], to which an orchestra tunes.
 
*A baby can hear tones with oscillations up to approximately 20,000 Hz, but these frequencies become more difficult to hear as people age.
 
*A baby can hear tones with oscillations up to approximately 20,000 Hz, but these frequencies become more difficult to hear as people age.
*In Europe, the frequency of the [[alternating current]] in [[mains electricity|mains]] is 50 Hz (close to the tone G), however, in North America, the frequency of the [[alternating current]] is 60 Hz (close to the tone B flat — that is, a [[minor third]] above the European frequency). The frequency of the '[[hum]]' in an [[audio recording]] can show where the recording was made — in Europe, or in America.
+
   
 
== See also ==
 
== See also ==
{{portalpar|Electronics|Zenerdiod symbol.png}}
 
*[[Negative frequency]]
 
*[[Angular frequency]]
 
*[[Frequency converter]]
 
 
*[[Letter frequencies]]
 
*[[Letter frequencies]]
 
*[[Pitch (music)]]
 
*[[Pitch (music)]]
 
*[[Natural frequency]]
 
*[[Natural frequency]]
*[[Wavelength]]
 
 
==External links==
 
*[http://www.sengpielaudio.com/calculator-wavelength.htm Conversion: frequency to wavelength and back]
 
*[http://www.sengpielaudio.com/calculator-period.htm Conversion: period, cycle duration, periodic time to frequency]
 
*[http://www.sengpielaudio.com/calculator-notenames.htm Keyboard frequencies = naming of notes - The English and American system versus the German system]
 
 
[[Category:Physical quantity]]
 
[[Category:Acoustics]]
 
[[Category:Wave mechanics]]
 
[[Category:Qualities of thought]]
 
 
[[Image:Sine waves different frequencies.svg|thumb|right|360px|[[Sine wave]]s of various frequencies; the bottom waves have higher frequencies than those above.]]
 
'''Frequency''' is the [[measurement]] of the number of occurrences of a repeated event per unit of [[time]]. It is also defined as the rate of change of [[phase (waves)|phase]] of a [[sinusoid]]al waveform.
 
 
== Measurement ==
 
To calculate the frequency of the event, the number of occurrences of the event within a fixed time interval are counted, and then divided by the length of the time interval.
 
 
To calculate the frequency of an event in experimental work however (for example calculating the frequency of an oscillating pendulum) it is crucial that the time taken for a fixed number of occurrences is recorded, rather than the number of occurrences within a fixed time. This is because your [[random error]] is significantly increased performing the experiment the other way around. It [the frequency] is still calculated by dividing the number of occurrences by the time interval, however, the number of occurrences is fixed, not the time interval.
 
 
In [[SI]] units, the result is measured in [[Hertz|hertz (Hz)]], named after the German physicist [[Heinrich Rudolf Hertz]]. 1 Hz means that an event repeats once per [[second]], 2 Hz is twice per second, and so on. This unit was originally called a [[cycle per second]] (cps), which is still sometimes used. Other units that are used to measure frequency include [[revolutions per minute]] (rpm). [[Heart rate]] and musical [[tempo]] are measured in [[beats per minute]] (BPM).
 
Often, [[angular frequency]] is used instead of frequency, measured in [[radians per second]] (rad/s).
 
 
An alternative method to calculate frequency is to measure the time between two consecutive occurrences of the event (the period) and then compute the frequency ''f'' as the reciprocal of this time:
 
:<math>
 
f = \frac{1}{T}
 
</math>
 
where
 
:''T'' is the '''[[period (physics)|period]]'''.
 
 
A more accurate measurement takes many cycles into account and averages the period between each.
 
 
==Frequency of waves==
 
Frequency has an inverse relationship to the concept of [[wavelength]]. The frequency ''f'' is equal to the [[speed]] ''v'' of the [[wave]] [[division (mathematics)|divided]] by the [[wavelength]] λ (lambda) of the wave:
 
:<math>
 
f = \frac{v}{\lambda}
 
</math>
 
 
In the [[special case]] of electromagnetic waves moving through a [[vacuum]], then '''v = c''', where '''c''' is the [[speed of light]] in a vacuum, and this expression becomes:
 
:<math>
 
f = \frac{c}{\lambda}
 
</math>
 
 
When [[waves]] travel from one [[Medium (optics)|medium]] to another, their frequency remains exactly the same &mdash; only their [[wavelength]] and [[speed]] change.
 
 
Apart from being modified by the [[Doppler effect]] or any other nonlinear process, frequency is an invariant quantity in the universe. That is, it cannot be changed by any linearly physical process unlike velocity of propagation or wavelength.
 
 
Frequency is also a measure of temperature, as for when the temperature of a molecule is increased it will vibrate faster. The faster the molecule will vibrate the higher the frequency.
 
 
==Examples==
 
*The frequency of the standard pitch A above [[middle C]] is usually defined as [[A440|440 Hz]], that is, 440 cycles per second ({{Audio|Media-440Hz.ogg|Listen}}) and known as concert [[Pitch (music)|pitch]], to which an [[orchestra]] tunes.
 
*A baby can hear tones with oscillations up to approximately 20,000 Hz, but these frequencies become more difficult to hear as people age.
 
*In Europe, the frequency of the [[alternating current]] in [[mains electricity|mains]] is 50 Hz (close to the tone G), however, in North America, the frequency of the [[alternating current]] is 60 Hz (close to the tone B flat — that is, a [[minor third]] above the European frequency). The frequency of the '[[hum]]' in an [[audio recording]] can show where the recording was made — in Europe, or in America.
 
 
== See also ==
 
 
*[[Negative frequency]]
 
*[[Letter frequencies]]
 
*[[Pitch (music)]]
 
 
*[[Stimulus frequency]]
 
*[[Stimulus frequency]]
*[[Natural frequency]]
+
*[[Stimulus parameters]]
 
*[[Tempo]]
 
*[[Tempo]]
 
*[[Visual displays]]
 
*[[Visual displays]]
*[[Visual stimulATION]]
+
*[[Visual stimulation]]
 
*[[Wavelength]]
 
*[[Wavelength]]
   
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*[http://www.sengpielaudio.com/calculator-notenames.htm Keyboard frequencies = naming of notes - The English and American system versus the German system]
 
*[http://www.sengpielaudio.com/calculator-notenames.htm Keyboard frequencies = naming of notes - The English and American system versus the German system]
   
  +
  +
[[Category:Acoustics]]
 
[[Category:Physical quantity]]
 
[[Category:Physical quantity]]
[[Category:Acoustics]]
 
[[Category:Wave mechanics]]
 
 
[[Category:Qualities of thought]]
 
[[Category:Qualities of thought]]
+
[[Category:Tempo]]
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[[af:Frekwensie]]
 
[[ar:تردد]]
 
[[az:Tezlik]]
 
[[zh-min-nan:Pîn-lu̍t]]
 
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[[bg:Честота]]
 
[[ca:Freqüència]]
 
[[cs:Frekvence]]
 
[[da:Frekvens]]
 
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[[et:Sagedus]]
 
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[[ko:진동수]]
 
[[hr:Frekvencija]]
 
[[io:Frequeso]]
 
[[id:Frekuensi]]
 
[[it:Frequenza]]
 
[[he:תדירות]]
 
[[lt:Dažnis]]
 
[[hu:Frekvencia]]
 
[[mk:Фреквенција]]
 
[[mg:Hatetika]]
 
[[nl:Frequentie]]
 
[[ja:周波数]]
 
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[[nn:Frekvens i fysikk]]
 
[[pl:Częstotliwość]]
 
[[pt:Frequência]]
 
[[ro:Frecvenţă]]
 
[[ru:Частота]]
 
[[simple:Frequency]]
 
[[sk:Frekvencia (fyzika)]]
 
[[sl:Frekvenca]]
 
[[sr:Фреквенција]]
 
[[su:Frékuénsi]]
 
[[fi:Taajuus]]
 
[[sv:Frekvens]]
 
[[ta:அதிர்வெண்]]
 
[[th:ความถี่]]
 
[[vi:Tần số]]
 
[[tr:Frekans]]
 
[[zh:頻率]]--->
 
 
   
 
{{enWP|Frequency}}
 
{{enWP|Frequency}}

Latest revision as of 10:07, February 14, 2009

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Sine waves different frequencies

Sine waves of various frequencies; the bottom waves have higher frequencies than those above.

Frequency is the measurement of the number of occurrences of a repeated event per unit of time.

Measurement Edit

To calculate the frequency of the event, the number of occurrences of the event within a fixed time interval are counted, and then divided by the length of the time interval.

To calculate the frequency of an event in experimental work however (for example calculating the frequency of an oscillating pendulum) it is crucial that the time taken for a fixed number of occurrences is recorded, rather than the number of occurrences within a fixed time. This is because your random error is significantly increased performing the experiment the other way around. It [the frequency] is still calculated by dividing the number of occurrences by the time interval, however, the number of occurrences is fixed, not the time interval.

In SI units, the result is measured in hertz (Hz), named after the German physicist Heinrich Rudolf Hertz. 1 Hz means that an event repeats once per second, 2 Hz is twice per second, and so on. This unit was originally called a cycle per second (cps), which is still sometimes used. Other units that are used to measure frequency include revolutions per minute (rpm). Heart rate and musical tempo are measured in beats per minute (BPM). Often, angular frequency is used instead of frequency, measured in radians per second (rad/s).

An alternative method to calculate frequency is to measure the time between two consecutive occurrences of the event (the period) and then compute the frequency f as the reciprocal of this time:


f = \frac{1}{T}

where

T is the period.

A more accurate measurement takes many cycles into account and averages the period between each.

Frequency of wavesEdit

Frequency has an inverse relationship to the concept of wavelength. The frequency f is equal to the speed v of the wave divided by the wavelength λ (lambda) of the wave:


f = \frac{v}{\lambda}


When waves travel from one medium to another, their frequency remains exactly the same — only their wavelength and speed change.

Frequency is also a measure of temperature, as for when the temperature of a molecule is increased it will vibrate faster. The faster the molecule will vibrate the higher the frequency.

ExamplesEdit

) and known as concert pitch, to which an orchestra tunes.

  • A baby can hear tones with oscillations up to approximately 20,000 Hz, but these frequencies become more difficult to hear as people age.


See also Edit

External linksEdit

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