# Frequency

frequenciesperiodperiodicperiodicityƒcyclicalordinary frequencycycleoscillation frequencywave period
Frequency is the number of occurrences of a repeating event per unit of time.wikipedia
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Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.
Radio waves have frequencies as high as 300 gigahertz (GHz) to as low as 30 hertz (Hz).

### Light

visible lightvisiblelight source
Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.
This wavelength means a frequency range of roughly 430–750 terahertz (THz).

### Angular frequency

angular speedangular frequenciesangular
It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. * Angular frequency, usually denoted by the Greek letter ω (omega), is defined as the rate of change of angular displacement, θ, (during rotation), or the rate of change of the phase of a sinusoidal waveform (notably in oscillations and waves), or as the rate of change of the argument to the sine function:
T is the period (measured in seconds),

In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter \nu or ν (nu) (see e.g. Planck's formula).
Radio is the technology of using radio waves to carry information, such as sound and images, by systematically modulating properties of electromagnetic energy waves transmitted through space, such as their amplitude, frequency, phase, or pulse width.

### Acoustics

acousticacousticianacoustical
In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter \nu or ν (nu) (see e.g. Planck's formula).
Frequencies above and below the audible range are called "ultrasonic" and "infrasonic", respectively.

### Planck constant

reduced Planck constantPlanck's constantreduced Planck's constant
In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter \nu or ν (nu) (see e.g. Planck's formula).
, that was proportional to the frequency of its associated electromagnetic wave.

### Cycle per second

kilocyclecycles per secondkilocycles
A previous name for this unit was cycles per second (cps).
The cycle per second was a once-common English name for the unit of frequency now known as the hertz (Hz).

### Vibration

vibrationsvibratevibrating
Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.
Note: angular frequency ω (ω=2 π f) with the units of radians per second is often used in equations because it simplifies the equations, but is normally converted to ordinary frequency (units of Hz or equivalently cycles per second) when stating the frequency of a system.

### Spatial frequency

spatial frequenciesspace frequencyfrequency
It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency.
to represent temporal frequency.

### Revolutions per minute

rpmr.p.m.RPMs
A traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm.
It is a unit of rotational speed or the frequency of rotation around a fixed axis.

### SI derived unit

derived unitderived unitsJ/kg
The SI derived unit of frequency is the hertz (Hz), named after the German physicist Heinrich Hertz.

### Rotation

rotatingrotatespin
For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time.
The speed of rotation is given by the angular frequency (rad/s) or frequency (turns per time), or period (seconds, days, etc.).

### Second

ssecmegasecond
One hertz means that an event repeats once per second.
The second is also part of several other units of measurement like meters per second for velocity, meters per second per second for acceleration, and per second for frequency.

### Nu (letter)

nuΝGreek letter nu
In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter \nu or ν (nu) (see e.g. Planck's formula).
The frequency of a wave in physics and other fields; sometimes also spatial frequency; wavenumber

### Phase (waves)

phasephase shiftout of phase
* Angular frequency, usually denoted by the Greek letter ω (omega), is defined as the rate of change of angular displacement, θ, (during rotation), or the rate of change of the phase of a sinusoidal waveform (notably in oscillations and waves), or as the rate of change of the argument to the sine function:
Phase can also be an expression of relative displacement between two corresponding features (for example, peaks or zero crossings) of two waveforms having the same frequency.

### Dispersion relation

dispersiondispersion relationsdispersive
For periodic waves in nondispersive media (that is, media in which the wave speed is independent of frequency), frequency has an inverse relationship to the wavelength, λ (lambda).
A dispersion relation relates the wavelength or wavenumber of a wave to its frequency.

### Wavelength

wavelengthsperiodsubwavelength
For periodic waves in nondispersive media (that is, media in which the wave speed is independent of frequency), frequency has an inverse relationship to the wavelength, λ (lambda).
Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to frequency of the wave: waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths.

### Wave

wavestravelling wavetraveling wave
For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. Even in dispersive media, the frequency f of a sinusoidal wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave:
The phase velocity is given in terms of the wavelength (lambda) and period as

### Sine wave

sinusoidalsinusoidsine
* Angular frequency, usually denoted by the Greek letter ω (omega), is defined as the rate of change of angular displacement, θ, (during rotation), or the rate of change of the phase of a sinusoidal waveform (notably in oscillations and waves), or as the rate of change of the argument to the sine function:
f = the ordinary frequency, the number of oscillations (cycles) that occur each second of time.

### Wind wave

waveswavewave dominated
As a matter of convenience, longer and slower waves, such as ocean surface waves, tend to be described by wave period rather than frequency.
Wave period (time interval between arrival of consecutive crests at a stationary point)

### International System of Units

SISI unitsSI unit
The SI unit for period is the second.

### Phase velocity

phase speedphase velocitiesphase
Even in dispersive media, the frequency f of a sinusoidal wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave:
This is the velocity at which the phase of any one frequency component of the wave travels.

### Frequency counter

digital frequency counterselectronic countersfrequency counters
Higher frequencies are usually measured with a frequency counter.
A frequency counter is an electronic instrument, or component of one, that is used for measuring frequency.

### Quartz clock

quartz watchquartzquartz movement
It uses digital logic to count the number of cycles during a time interval established by a precision quartz time base.
This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than mechanical clocks.

### Sound

audiosound wavesound waves
Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.
Humans can only hear sound waves as distinct pitches when the frequency lies between about 20 Hz and 20 kHz.