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Encyclopedia > Frequency

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. ...

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

## 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 (Î¼Ï‰Î½Î¿, meaning one), and chroma (Ï‡ÏÏ‰Î¼Î±, 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. ...

## 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 Period (time) 1 mHz (10-3) 1 Hz (100) 1 kHz (103) 1 MHz (106) 1 GHz (109) 1 THz (1012) 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): $omega=2pi f,$.
• 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[Ï‰(x âˆ’ Î±)] + C where A is the amplitude, Ï‰ is the angular frequency (2Ï€/P where P is the wavelength), Î± 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 (mâˆ’1). ... Look up vector in Wiktionary, the free dictionary. ...

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. ... 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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