Frequency
From HvWiki
Frequency (Hz) is the number of times a repeated event occurs per unit of time.
The frequency of an event is also the number of times the event occurred in an experiment.
See Frequency under units.
Often textbooks talk of angular frequency, usually designated ω. This the number of radians an oscillator cycles through every second. Since the usual frequency is just cycles per second, and there are two π radians per cycle, this means simply, ω = 2πf. Strictly, angular frequency is not measured in Hertz, but s − 1.
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Examples of Frequency
Musical Frequency
Higher pitched sounds are actually higher frequency mechanical vibrations. Middle C on a piano is commonly defined as 512Hz. Going up or down an octave doubles or halves the frequency. Thus C above middle C is 1024Hz and C below middle C is 256Hz.
AC Electrical Frequency
When electrical engineers talk of frequency, they are generally referring to the rate at which the voltage of a circuit changes. A voltage that is zero, then positive, then zero, then negative and back to zero again in exactly one second is a 1Hz voltage.
Mains power is typically 50Hz (as in Australia) or 60Hz (as in the US).
Many electrical devices work in different ways at different frequencies. A transformer is generally designed to work at a particular frequency, although it can usually be run at a slightly higher frequency. A capacitor has a lower reactance at higher frequency, while an inductor's reactance goes up with frequency.
Radio Frequency
Really this is not distinct from the above but it is used commonly enough in its own context. Radio stations and other sources of radio waves produce signals modulated ("encoded") on a radio wave, called a carrier, of a specified freqency.
Colour
In a rainbow, the colours near red are lower frequency forms of electromagnetic radiation than those near blue. The spectrum extends out further each way to invisible forms of EMR. This is usually called the electromagnetic spectrum.
