Dictionary Definition
frequency
Noun
1 the number of occurrences within a given time
period (usually 1 second); "the frequency of modulation was 40
cycles per second" [syn: frequence, oftenness]
2 the ratio of the number of observations in a
statistical category to the total number of observations [syn:
relative
frequency]
3 the number of observations in a given
statistical category [syn: absolute
frequency]
User Contributed Dictionary
English
Pronunciation
 /ˈfriːkwənsi/
 /"fri:kw@nsi/
Noun
 The rate of occurrence of anything; the
relationship between incidence and time period.
 With growing confidence, the Viking’s raids increased in frequency.
 The frequency of bus service has been improved from 15 to 12 minutes.
 The property of
occurring often rather than infrequently.
 The FAQ addresses questions that come up with some frequency.
 The frequency of the visits was what annoyed him.
 The quotient of the
number of times n a periodic phenomenon occurs over the
time t in which it occurs:
f = n / t.
 The frequency of middle C is 440 oscillations per second.
 The frequency of a wave is its velocity v divided by its wavelength \lambda: f = v / \lambda.
 Broadcasting live at a frequency of 98.3 megahertz, we’re your rock alternative!
 The frequency for electric power in the Americas is generally 60 Hz rather than 50.''
Translations
rate of occurrence of anything
 Chinese:
 Czech: četnost
 Danish: hyppighed
 Dutch: frequentie
 Finnish: taajuus, frekvenssi (statistical)
 German: Häufigkeit , Frequenz , Regelmäßigkeit
 Greek: συχνότητα (sychnotita or sihnotita)
 Hebrew:
 Hungarian: gyakoriság, ismétlődés
 Italian: frequenza
 Japanese: (, hindo)
 Malay: kekerapan
 Portuguese: frequência
 Russian: частота
 Slovenian: pogostost
 Vietnamese: tính thường xuyên
property of occurring often rather than
infrequently
 Dutch: regelmaat
 German: Häufigkeit
 Hungarian: gyakoriság
 Malay: kekerapan
number of occurrences divided by time
 Bulgarian: честота
 Chinese:
 Czech: frekvence, kmitočet i of radio frequency
 Danish: frekvens
 Dutch: frequentie
 Finnish: taajuus
 French: fréquence
 German: Frequenz
 Greek: συχνότητα (sychnotita or sihnotita)
 Hebrew: , (used for a radio station or a twoway radio device)
 Hungarian: frekvencia
 Icelandic: tíðni
 Italian: frequenza
 Japanese: (, shūhasū)
 Latvian frekvence
 Malay: frekuensi
 Portuguese: frequência
 Russian: частота (častotá)
 Slovenian: frekvenca , pogostost
 Spanish: frecuencia
 Swedish: frekvens
 Vietnamese: tần số
 ttbc Catalan: freqüència
 ttbc Esperanto: frekvenco
 ttbc Faroese: tíðføri , tíðleiki , tídd
 ttbc Indonesian: frekuensi
 ttbc Latin: freuqentia
 ttbc Lithuanian: dažnumas
 ttbc Norwegian: frekvens
 ttbc Polish: częstotliwość
 ttbc Slovak: frekvencia
 ttbc Tamil: அதிர்வெண்
 ttbc Telugu: పౌనఃపున్యము (paunahpunyamu)
 ttbc Turkish: frekans
Extensive Definition
Frequency is a measure of the number of
occurrences of a repeating event per unit time. It is also referred to as
temporal frequency. The period is the duration of one cycle in a repeating event, so the
period is the reciprocal
of the frequency.
Definition and units
For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles, or periods, per unit time. In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by a Greek letter ν (nu).In SI
units, the unit of frequency is hertz (Hz), named
after the German physicist Heinrich
Hertz. For example, 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. Heart rate and
musical tempo are measured
in beats per
minute (BPM). Frequency of rotation is often expressed as a
number of revolutions
per minute (rpm). BPM and rpm values must be divided by 60 to
obtain the corresponding value in Hz: thus, 60 BPM translates into 1
Hz.
The period is usually denoted as T, and is the
reciprocal
of the frequency f: T = \frac.
The SI unit for period is the second (s).
Measurement
By timing
To calculate the frequency of an 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.In experimental work (for example, calculating
the frequency of an oscillating pendulum) it is more accurate to
measure the time taken for a fixed number of occurrences, rather
than the number of occurrences within a fixed time. The latter
method introduces a random error
of 1/f Hz into the result. Frequency is still calculated by
dividing the number of occurrences by the time interval; however it
is the number of occurrences that is fixed, not the time
interval.
An alternative method to calculate frequency is
to measure the time between two consecutive occurrences of the
event (the period T) and then compute the frequency f as the
reciprocal of this time: f = \frac.
A more accurate measurement can be obtained by
taking many cycles into account and averaging the periods between
each.
By stroboscope effect, or frequency beats
In case when the frequency is so high that counting is difficult or impossible with the available means, another method is used, based on a source (such as a laser, a tuning fork, or a waveform generator) of a known reference frequency f0, that must be tunable or very close to the measured frequency f. Both the observed frequency and the reference frequency are simultaneously produced, and frequency beats are observed at a much lower frequency Δf, which can be measured by counting. This is sometimes referred to as a stroboscope effect. The unknown frequency is then found from f=f_0\pm \Delta f.Frequency of waves
Frequency has an inverse relationship to the
concept of wavelength, simply, frequency
is inversely proportional to wavelength λ (lambda). The frequency f
is equal to the speed v of
the wave divided
by the wavelength λ of the wave: f = \frac.
In the special case
of electromagnetic waves moving through a vacuum, then v = c0 , where c0 is
the speed of
light in a vacuum, and this expression becomes: f =
\frac.
When waves from a monochromatic source travel
from one medium to
another, their frequency remains exactly the same — only their
wavelength and
speed change.
Examples
 In music and acoustics, the frequency of the standard pitch A above middle C on a piano is usually defined as 440 Hz, that is, 440 cycles per second (Listen) 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.
 In Europe, Africa, Australia, Southern South America, most of Asia, and in Russia, the frequency of the alternating current in household electrical outlets is 50 Hz (close to the tone G), however, in North America and Northern South America, the frequency of the alternating current is 60 Hz (between the tones B♭ and B — 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 countries utilizing the European, or the American grid frequency.
 Visible light from deep red to violet has frequencies of 430 to 750 THz.
Period versus frequency
As a matter of convenience, longer and slower waves, such as ocean surface waves, tend to be described by wave period rather than frequency. Short and fast waves, like audio and radio, are usually described by their frequency instead of period. These commonly used conversions are listed below:Other types of frequency
 Angular frequency ω is defined as the rate of change in the orientation angle (during rotation), or in the phase of a sinusoidal waveform (e.g. in oscillations and waves):

 \omega=2\pi f\,.
 Angular frequency is measured in radians per second (rad/s).
 Spatial frequency is analogous to temporal frequency, but the time axis is replaced by one or more spatial displacement axes.
 Wavenumber is the spatial analogue of angular frequency. In case of more than one space dimension, wavenumber is a vector quantity.
See also
References
External links
 National Research Council of Canada: Femtosecond comb; The measurement of optical frequencies
 Conversion: frequency to wavelength and back
 Conversion: period, cycle duration, periodic time to frequency
 Keyboard frequencies = naming of notes  The English and American system versus the German system
 Teaching resource for 1416yrs on sound including frequency
 A simple tutorial on how to build a frequency meter
 Frequency  diracdelta.co.uk  javascript calculation.
frequency in Afrikaans: Frekwensie
frequency in Arabic: تردد
frequency in Asturian: Frecuencia
frequency in Azerbaijani: Tezlik
frequency in Bengali: কম্পাঙ্ক
frequency in Min Nan: Pînlu̍t
frequency in Bosnian: Frekvencija
frequency in Bulgarian: Честота
frequency in Catalan: Freqüència
frequency in Czech: Frekvence
frequency in Danish: Frekvens
frequency in German: Frequenz
frequency in Estonian: Sagedus
frequency in Modern Greek (1453):
Συχνότητα
frequency in Spanish: Frecuencia
frequency in Esperanto: Frekvenco
frequency in Basque: Maiztasun
frequency in Persian: بسامد
frequency in French: Fréquence
frequency in Galician: Frecuencia
frequency in Korean: 진동수
frequency in Hindi: आवृत्ति
frequency in Croatian: Frekvencija
frequency in Ido: Frequeso
frequency in Indonesian: Frekuensi
frequency in Icelandic: Tíðni
frequency in Italian: Frequenza
frequency in Hebrew: תדירות
frequency in Latin: Frequentia
frequency in Latvian: Frekvence
frequency in Lithuanian: Dažnis
frequency in Hungarian: Frekvencia
frequency in Macedonian: Фреквенција
frequency in Malagasy: Hatetika
frequency in Malay (macrolanguage):
Frekuensi
frequency in Mongolian: Давтамж
frequency in Dutch: Frequentie
frequency in Japanese: 周波数
frequency in Norwegian: Frekvens
frequency in Norwegian Nynorsk: Frekvens i
fysikk
frequency in Polish: Częstotliwość
frequency in Portuguese: Frequência
frequency in Romanian: Frecvenţă
frequency in Russian: Частота
frequency in Simple English: Frequency
frequency in Slovak: Frekvencia (fyzika)
frequency in Slovenian: Frekvenca
frequency in Serbian: Фреквенција
frequency in Sundanese: Frékuénsi
frequency in Finnish: Taajuus
frequency in Swedish: Frekvens
frequency in Tamil: அதிர்வெண்
frequency in Thai: ความถี่
frequency in Vietnamese: Tần số
frequency in Cherokee: ᎠᏍᏓᏩᏛᏍᏙᏗ
frequency in Turkish: Frekans
frequency in Ukrainian: Частота
frequency in Urdu: تعدد
frequency in Samogitian: Tonkėnis
frequency in Chinese: 頻率
Synonyms, Antonyms and Related Words
AF,
CPS, EHF, HF, Hz, MF, RF, SHF, UHF, VHF, VLF, amplitude, antinode, audio frequency,
carrier frequency, crest,
cycles, de Broglie wave,
diffraction,
electromagnetic radiation, electromagnetic wave, extremely high
frequency, fluctuation, frequency band,
frequency spectrum, fundamental, fundamental
tone, guided wave, harmonic, harmonic motion,
hertz, high frequency, in
phase, interference, intermediate
frequency, intonation, kilocycles, kilohertz, libration, light, longitudinal wave, low
frequency, lower frequencies, mechanical wave, medium frequency,
megacycles, megahertz, monotone, monotony, node, nutation, oscillation, out of phase,
overtone, partial, partial tone, pendulation, period, periodic wave, periodicity, pitch, radio frequency, radio
wave, ray, reinforcement, resonance, resonance
frequency, seismic wave, shock wave, sound wave, spark frequency,
spectrum, superhigh
frequency, surface wave, tidal wave, tone, tonelessness, transverse
wave, trough, ultrahigh
frequency, upper frequencies, vacillation, very high
frequency, very low frequency, vibrancy, vibratility, vibration, wave, wave equation, wave motion,
wave number, wavelength, wavering