 - For an oscillating or varying current, frequency is
the number of complete cycles per second in alternating current direction. The standard
unit of frequency is the hertz, abbreviated
Hz. If a current completes
one cycle per second, then the frequency is 1 Hz; 60 cycles per
second equals 60 Hz (the
standard alternating-current utility frequency in some countries).
Larger units of frequency include the
kilohertz (kHz)
representing thousands (1,000's) of cycles per second, the
megahertz (MHz)
representing millions (1,000,000's) of cycles per second, and
the gigahertz (GHz)
representing billions (1,000,000,000's) of cycles per
second. Occasionally the terahertz
(THz) is used; 1 THz = 1,000,000,000,000 cycles per
second. Note that these prefixes
represent specific powers of 10, in contrast to the prefixes for
multiples of bytes, which
represent specific powers of 2.
Computer clock speed is generally specified in
megahertz and, more recently, in gigahertz.
Frequency is important in wireless
communications, where the frequency of a signal is
mathematically related to the wavelength. If
f is the frequency
of an electromagnetic
field in free space as
measured in megahertz, and w is the wavelength as
measured in meters, then
w = 300/f
and conversely
f = 300/w
Also see the definitions of signal
and electromagnetic radiation spectrum.
| LAST UPDATED: |
27 Jul 2001
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