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Encyclopedia > Frequency
Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above. The horizontal axis represents time.
Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above. The horizontal axis represents time.

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. Frequency can refer to: Frequency, measurement of signal wave cycles Frequency, a 2000 film starring Jim Caviezel and Dennis Quaid FreQuency, a music video game FM4 Frequency Festival, an Austrian music festival In statistics, the (statistical) frequency of an event is the number of times the event occurred in the... Image File history File links Sine_waves_different_frequencies. ... Image File history File links Sine_waves_different_frequencies. ... Sinusoid redirects here. ... Measurement is the estimation of the magnitude of some attribute of an object, such as its length or weight, relative to a unit of measurement. ... This article is about the concept of time. ... A duration is an amount of time or a particular time interval. ... Cycle or Cycles may be: Look up cycle in Wiktionary, the free dictionary. ... The reciprocal function: y = 1/x. ...

Contents

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). Cycle or Cycles may be: Look up cycle in Wiktionary, the free dictionary. ... This article is about rotation as a movement of a physical body. ... Oscillation is the variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. ... Surface waves in water This article is about waves in the most general scientific sense. ... Cycle or Cycles may be: Look up cycle in Wiktionary, the free dictionary. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... Engineering is the discipline and profession of applying scientific knowledge and utilizing natural laws and physical resources in order to design and implement materials, structures, machines, devices, systems, and processes that realize a desired objective and meet specified criteria. ... For the book by Sir Isaac Newton, see Opticks. ... Acoustics is the interdisciplinary sciences that always deals with the study of sound, ultrasound and infrasound (all mechanical waves in gases, liquids, and solids). ...


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 [1]. 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. SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ... This article is about the SI unit of frequency. ... Heinrich Rudolf Hertz (February 22, 1857 - January 1, 1894) was the German physicist and mechanician for whom the hertz, an SI unit, is named. ... This article is about the unit of time. ... A once-common unit of frequency. ... Heart rate is the frequency of the cardiac cycle. ... For other uses, see Tempo (disambiguation). ... Beats per minute (bpm) is a unit typically used as either a measure of tempo in music, or a measure of ones heart rate. ... For other uses, see Revolutions per minute (disambiguation). ... This article is about the SI unit of frequency. ...


The period is usually denoted as T, and is the reciprocal of the frequency f: The reciprocal function: y = 1/x. ...

 T = frac{1}{f}.

The SI unit for period is the second (s). This article is about the unit of time. ...


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 — if N is the number of counted occurrences — a random error between zero and one count, so on average half a count, causing an biased underestimation of f by ½ f / (N + ½) in its expected value. In the first method, which is more accurate, 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. In statistics, the concepts of error and residual are easily confused with each other. ... Averages redirects here. ... In statistics, the term bias is used for two different concepts. ... In probability theory the expected value (or mathematical expectation) of a random variable is the sum of the probability of each possible outcome of the experiment multiplied by its payoff (value). Thus, it represents the average amount one expects as the outcome of the random trial when identical odds are...


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{1}{T}.

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_0pm Delta f. For other uses, see Laser (disambiguation). ... A tuning fork is a simple metal two-pronged fork with the tines formed from a U-shaped bar of elastic material (usually steel). ... It has been suggested that this article or section be merged with Function generator. ... In acoustics, a beat is an interference between two sounds of slightly different frequencies, perceived as periodic variations in volume whose rate is the difference between the two frequencies. ... A stroboscope , also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving or stationary. ...


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: For other uses, see Wavelength (disambiguation). ... The phase velocity of a wave is the rate at which the phase of the wave propagates in space. ... Surface waves in water This article is about waves in the most general scientific sense. ... In mathematics, especially in elementary arithmetic, division is an arithmetic operation which is the inverse of multiplication. ...

 f = frac{v}{lambda}.

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: A special case is generally an unexpected circumstance which may occur but should usually not. ... Look up Vacuum in Wiktionary, the free dictionary. ... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ...

 f = frac{c_0}{lambda}.

When waves from a monochromatic source travel from one medium to another, their frequency remains exactly the same — only their wavelength and speed change. A WAVES Photographer 3rd Class The WAVES were a World War II era division of the U.S. Navy that consisted entirely of women. ... A photograph of a sign in grayscale The same photograph in black and white Monochrome comes from the two Greek words mono (μωνο, meaning one), and chroma (χρωμα, meaning surface or the color of the skin). A monochromatic object has a single color. ... Free space is the most simple and elementary electromagnetic medium. ... For other uses, see Wavelength (disambiguation). ... This article does not cite any references or sources. ...


Examples

For other uses, see Music (disambiguation). ... Acoustics is the interdisciplinary sciences that always deals with the study of sound, ultrasound and infrasound (all mechanical waves in gases, liquids, and solids). ... This article is about the use of the term note in music. ... In Western music, the expression middle C refers to the note C or Do located exactly between the two staves of the grand staff, quoted as C4 in note-octave notation (also known as scientific pitch notation). ... Pianoforte redirects here. ... A440 is the 440 Hz tone that serves as the standard for musical pitch. ... Image File history File links Media-440Hz. ... Pitch is the perceived fundamental frequency of a sound. ... For other uses, see Orchestra (disambiguation). ... For other uses, see Europe (disambiguation). ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... For other uses, see Asia (disambiguation). ... City lights viewed in a motion blurred exposure. ... Type F mains power plug & socket The term mains usually refers to the general purpose alternating current (AC) electrical power supply (as in “Ive connected the appliance to the mains”). The term is not usually used in the United States and Canada. ... This article is about the use of the term note in music. ... North American redirects here. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... City lights viewed in a motion blurred exposure. ... This article is about the use of the term note in music. ... A minor third is the smaller of two commonly occurring musical intervals compounded of two steps of the diatonic scale. ... Spectrum of mains hum at 60 Hz Electric hum, mains hum, or power line hum is an audible oscillation at the frequency of the mains alternating current, which is usually 50 or 60 hertz depending on the local electric utility configuration (see Mains electricity). ... Methods and media for sound recording are varied and have undergone significant changes between the first time sound was actually recorded for later playback until now. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ...

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: For the TV movie also known as The Ocean Waves, see I Can Hear the Sea. ... This article is about audible acoustic waves. ...

Frequency 1 mHz (10-3) 1 Hz (100) 1 kHz (103) 1 MHz (106) 1 GHz (109) 1 THz (1012)
Period (time) 1 ks (103) 1 s (100) 1 ms (10-3) 1 µs (10-6) 1 ns (10-9) 1 ps (10-12)

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=2pi 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.

It has been suggested that this article or section be merged into Angular velocity. ... This article is about a portion of a periodic process. ... A sine wave or sinusoid is a waveform whose graph is identical to the generalized sine function y = Asin[ω(x − α)] + C where A is the amplitude, ω is the angular frequency (2π/P where P is the wavelength), α is the phase shift, and C is the vertical offset. ... For the musical group, see Radian (band). ... In mathematics, physics, and engineering, spatial frequency is a characteristic of any structure that is periodic across position in space. ... Wavenumber in most physical sciences is a wave property inversely related to wavelength, having SI units of reciprocal meters (m−1). ... Look up vector in Wiktionary, the free dictionary. ...

See also

Electronics Portal

Image File history File links Nuvola_apps_ksim. ... Negative frequency is the rate of clockwise rotation in phase, where phase is defined as the arctangent of the imaginary and real parts of an electrical signal or mathematical function. ... Periodicity is the quality of occurring at regular intervals (e. ... A frequency converter is a power electronic device, which transforms DC voltage to AC voltage of desired frequency and magnitude. ... The frequency range is defined as the range of frequencies in which the device is allowed to operate. ... The frequency of letters in text has often been studied for use in cryptography, and frequency analysis in particular. ... Pitch is the perceived fundamental frequency of a sound. ... fdg--220. ...

References

  1. ^ Accidentally, 1 hertz is the approximate frequency of a human heart (Herz in German language)

This article is about the SI unit of frequency. ... German (called Deutsch in German; in German the term germanisch is equivalent to English Germanic), is a member of the western group of Germanic languages and is one of the worlds major languages. ...

External links

Look up frequency, often in Wiktionary, the free dictionary.
  • 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 14-16yrs on sound including frequency
  • A simple tutorial on how to build a frequency meter
  • Frequency - diracdelta.co.uk - javascript calculation.
Wikipedia does not have an article with this exact name. ... Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 151 languages. ...

  Results from FactBites:
 
frequency :: The Snowboarders Journal - Snowboard (280 words)
Snowboarding’s original coffee-table journal and true voice, frequency TSJ publishes four issues per year in limited editions.
Covering snowboarding's global travel, landscapes, and personalities, frequency is snowboarding's true voice.
Although Baker had been closed for a month and a half and temperatures were hitting 70 degrees in Bellingham this Sunday, I couldn’t get snowboarding off my mind.
frequency - a definition from Whatis.com (254 words)
For an oscillating or varying current, frequency is the number of complete cycles per second in alternating current direction.
The standard unit of frequency is the hertz, abbreviated Hz.
Frequency is important in wireless communications, where the frequency of a signal is mathematically related to the wavelength.
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