Frequency: Difference between revisions
imported>Milton Beychok m (Copy edits) |
imported>Mark Widmer (Added value of speed of sound in air. Cleaned up language regarding photons and Planck's constant. Added list of typical frequency values.) |
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'''Frequency''' is a property of an [[oscillation]], [[vibration]], or other regularly-repeating (cyclic) phenomenon. The frequency of such a phenomenon is the number of repetitions (cycles) in a unit of [[time]]. In the [[SI]] system of units, frequency is measured in [[Hertz]] ('''Hz'''), the number of repetitions in one [[second]]. | '''Frequency''' is a property of an [[oscillation]], [[Vibrational spectrum|vibration]], or other regularly-repeating (cyclic) phenomenon. The frequency of such a phenomenon is the number of repetitions (cycles) in a unit of [[time]]. In the [[SI]] system of units, frequency is measured in [[Hertz]] ('''Hz'''), the number of repetitions in one [[second]]. | ||
Frequency ( '''''f''''' ) is the reciprocal of the period ( '''''T''''' ), which is the time interval over which the phenomenon repeats: | |||
:<math> | :<math>{f} = \frac{1}{T} \,\!</math> | ||
In electromagnetic radiation, the [[energy]] of | For a wave propagating through space, frequency ( '''''f''''' ) is inversely proportional to [[wavelength]] ( '''''λ''''' ), which is a length measurement: | ||
:<math>\lambda = \frac{c}{f} \,\!</math>, where '''''c''''' is the speed of propagation of the wave. | |||
For [[electromagnetic radiation]] in a vacuum, '''''c''''' = 299 792 458 m/s, the [[speed of light]]. For sound in air at 20 Celsius and atmospheric pressure, '''''c''''' = 343 m/s. | |||
In electromagnetic radiation, the [[energy]] ( '''''E''''' ) of a single photon is proportional to the frequency: | |||
:<math>E=hf \,\!</math> , where '''''h''''' = 6.626 x 10<sup>-34</sup> J•s ([[Planck's constant]]) | :<math>E=hf \,\!</math> , where '''''h''''' = 6.626 x 10<sup>-34</sup> J•s ([[Planck's constant]]) | ||
For waves encountered in everyday life, typical frequencies are 20 to 20,000 Hz for audible sound, 1 MHz for AM radio waves, 100 MHz for FM radio waves, and 430 to 750 THz for visible light. | |||
Non-wave phenomena can also be periodic and have an associated frequency. Household electricity is typically either 50 or 60 Hz, depending on location. A car engine running at a modest 1000 rpm has a 17 Hz frequency. Earth's once-per-day rotation corresponds to about 1 milliHz, and its once-per-year revolution about the Sun corresponds to about 3 nanoHz. | |||
Latest revision as of 20:29, 21 July 2020
Frequency is a property of an oscillation, vibration, or other regularly-repeating (cyclic) phenomenon. The frequency of such a phenomenon is the number of repetitions (cycles) in a unit of time. In the SI system of units, frequency is measured in Hertz (Hz), the number of repetitions in one second.
Frequency ( f ) is the reciprocal of the period ( T ), which is the time interval over which the phenomenon repeats:
For a wave propagating through space, frequency ( f ) is inversely proportional to wavelength ( λ ), which is a length measurement:
- , where c is the speed of propagation of the wave.
For electromagnetic radiation in a vacuum, c = 299 792 458 m/s, the speed of light. For sound in air at 20 Celsius and atmospheric pressure, c = 343 m/s.
In electromagnetic radiation, the energy ( E ) of a single photon is proportional to the frequency:
- , where h = 6.626 x 10-34 J•s (Planck's constant)
For waves encountered in everyday life, typical frequencies are 20 to 20,000 Hz for audible sound, 1 MHz for AM radio waves, 100 MHz for FM radio waves, and 430 to 750 THz for visible light.
Non-wave phenomena can also be periodic and have an associated frequency. Household electricity is typically either 50 or 60 Hz, depending on location. A car engine running at a modest 1000 rpm has a 17 Hz frequency. Earth's once-per-day rotation corresponds to about 1 milliHz, and its once-per-year revolution about the Sun corresponds to about 3 nanoHz.