frequency
, in
physics
, the 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
. 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 around
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.
Britannica Quiz
Physics and Natural Law
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 usually used to describe the angular frequency?that is, how much an object rotates or revolves in radians per unit time. 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
wavenumber
, the number of waves in a unit of distance, is sometimes used.