Noun

Singular frequency

Plural frequencies

frequency (plural frequencies)

1. (uncountable) The rate of occurrence of anything; the relationship between incidence and time period.
   • With growing confidence, the Viking’s raids increased in frequency.
   • The frequency of bus service has been improved from 15 to 12 minutes.
2. (uncountable) The property of occurring often rather than infrequently.
   • The FAQ addresses questions that come up with some frequency.
   • The frequency of the visits was what annoyed him.
3. (countable) The quotient of the number of times n a periodic phenomenon occurs over the time t in which it occurs: f = n / t.
   • The frequency of the musical note A above middle C is 440 oscillations per second.
   • The frequency of a wave is its velocity v divided by its wavelength λ: f = v / λ.
   • Broadcasting live at a frequency of 98.3 megahertz, we’re your rock alternative!
   • The frequency for electric power in the Americas is generally 60 Hz rather than 50.

Frequency is 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.

Definitions and units

For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles 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).

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.

A traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated RPM. 60 RPM equals one hertz.

The period is usually denoted as T, and is the reciprocal of the frequency f:

The SI unit for period is the second.

Measurement