# frequency

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frequency
/free"kweuhn see/, n., pl. frequencies.
1. Also, frequence. the state or fact of being frequent; frequent occurrence: We are alarmed by the frequency of fires in the neighborhood.
2. rate of occurrence: The doctor has increased the frequency of his visits.
3. Physics.
a. the number of periods or regularly occurring events of any given kind in unit of time, usually in one second.
b. the number of cycles or completed alternations per unit time of a wave or oscillation. Symbol: F; Abbr.: freq.
4. Math. the number of times a value recurs in a unit change of the independent variable of a given function.
5. Statistics. the number of items occurring in a given category. Cf. relative frequency.
[1545-55; < L frequentia assembly, multitude, crowd. See FREQUENT, -CY]
Syn. 1. regularity, repetition, recurrence.

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Number of waves that pass a fixed point per unit time; also, the number of cycles or vibrations undergone in unit time by a body in periodic motion.

Frequency f is the reciprocal of the time T taken to complete one cycle (the period), or 1/T. The frequency with which earth rotates is once per 24 hours. Frequency is usually expressed in units called hertz (Hz). One hertz is equal to one cycle per second; one kilohertz (kHz) is 1,000 Hz, and one megahertz (MHz) is 1,000,000 Hz. The musical pitch A above middle C (the A string of a violin) has been widely standardized as 440 Hz.

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in physics, number of waves that pass a fixed point in unit time; also the number of cycles or vibrations undergone during one unit of time by a body in periodic motion (q.v.). A body in periodic motion is said to have undergone one cycle or one vibration after passing through a series of events or positions and returning to its original state. See also angular velocity; simple harmonic motion.

If the period, or time interval, required to complete one cycle or vibration is 1/2 second, the frequency is 2 per second; if the period is 1/100 of an hour, the frequency is 100 per hour. In general, the frequency is the reciprocal of the period, or time interval—i.e., frequency = 1/period = 1/(time interval). The frequency with which the Moon revolves about the Earth is slightly more than 12 cycles per year; the frequency of the A string of a violin is 440 vibrations or cycles per second.

The symbols most often used for frequency are f and the Greek letters nu (ν) and omega (ω). Nu is used more often when specifying electromagnetic waves, such as light, X rays, and gamma rays; omega is mostly used by electrical engineers in referring to alternating current. Usually frequency is expressed in the hertz unit, named in honour of the 19th-century German physicist Heinrich Rudolf Hertz, one hertz being equal to one cycle per second, abbreviated Hz; one kilohertz (kHz) is 1,000 Hz, and one megahertz (MHz) is 1,000,000 Hz.

In spectroscopy another unit of frequency, the wave number (q.v.), is sometimes used.

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Universalium. 2010.

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