AskDefine | Define frequency

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

Etymology

From frequens + -t- + -ia.

Pronunciation

  • /ˈfriːkwənsi/
  • /"fri:kw@nsi/

Noun

  1. 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.
  2. 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.
  3. 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
property of occurring often rather than infrequently
  • Dutch: regelmaat
  • German: Häufigkeit
  • Hungarian: gyakoriság
  • Malay: kekerapan
number of occurrences divided by time
  • Bulgarian: честота
  • Chinese:
    Mandarin: (pín)
  • 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 two-way 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

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

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.

References

frequency in Afrikaans: Frekwensie
frequency in Arabic: تردد
frequency in Asturian: Frecuencia
frequency in Azerbaijani: Tezlik
frequency in Bengali: কম্পাঙ্ক
frequency in Min Nan: Pîn-lu̍t
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
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