AskDefine | Define often

Dictionary Definition

often adv
1 many times at short intervals; "we often met over a cup of coffee" [syn: frequently, oftentimes, oft, ofttimes] [ant: rarely, infrequently]
2 frequently or in great quantities; "I don't drink much"; "I don't travel much" [syn: much, a great deal]

User Contributed Dictionary

English

Etymology

From oft.

Pronunciation

  • (UK) /ˈɒfn/, /ˈɒftən/, /"Qfn/, /"Qft@n/
  • (US) /ˈɔːfn/, /ˈɔːftən/, /"O:fn/, /"O:ft@n/
  • Rhymes: -ɒfən
  • Hyphenation: of·ten

Translations

Frequently, many times

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

often in Afrikaans: Frekwensie
often in Arabic: تردد
often in Asturian: Frecuencia
often in Azerbaijani: Tezlik
often in Bengali: কম্পাঙ্ক
often in Min Nan: Pîn-lu̍t
often in Bosnian: Frekvencija
often in Bulgarian: Честота
often in Catalan: Freqüència
often in Czech: Frekvence
often in Danish: Frekvens
often in German: Frequenz
often in Estonian: Sagedus
often in Modern Greek (1453-): Συχνότητα
often in Spanish: Frecuencia
often in Esperanto: Frekvenco
often in Basque: Maiztasun
often in Persian: بسامد
often in French: Fréquence
often in Galician: Frecuencia
often in Korean: 진동수
often in Hindi: आवृत्ति
often in Croatian: Frekvencija
often in Ido: Frequeso
often in Indonesian: Frekuensi
often in Icelandic: Tíðni
often in Italian: Frequenza
often in Hebrew: תדירות
often in Latin: Frequentia
often in Latvian: Frekvence
often in Lithuanian: Dažnis
often in Hungarian: Frekvencia
often in Macedonian: Фреквенција
often in Malagasy: Hatetika
often in Malay (macrolanguage): Frekuensi
often in Mongolian: Давтамж
often in Dutch: Frequentie
often in Japanese: 周波数
often in Norwegian: Frekvens
often in Norwegian Nynorsk: Frekvens i fysikk
often in Polish: Częstotliwość
often in Portuguese: Frequência
often in Romanian: Frecvenţă
often in Russian: Частота
often in Simple English: Frequency
often in Slovak: Frekvencia (fyzika)
often in Slovenian: Frekvenca
often in Serbian: Фреквенција
often in Sundanese: Frékuénsi
often in Finnish: Taajuus
often in Swedish: Frekvens
often in Tamil: அதிர்வெண்
often in Thai: ความถี่
often in Vietnamese: Tần số
often in Cherokee: ᎠᏍᏓᏩᏛᏍᏙᏗ
often in Turkish: Frekans
often in Ukrainian: Частота
often in Urdu: تعدد
often in Samogitian: Tonkėnis
often in Chinese: 頻率

Synonyms, Antonyms and Related Words

again and again, commonly, continually, day after day, day by day, frequently, habitually, in many instances, many a time, many times, many times over, most often, much, not infrequently, not seldom, oft, often enough, oftentimes, ofttimes, ordinarily, over and over, recurrently, regularly, repeatedly, routinely, several times, time after time, time and again, times without number, unseldom, usually, whenever you wish, year after year
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