Hertz

For people who check facts

The hertz (symbol Hz) is the SI unit of frequency. It is named in honor of the German physicist Heinrich Rudolf Hertz who made some important contributions to science in the field of electromagnetism.

One hertz simply means "one (event) per second"; 100 Hz means "one hundred (events) per second", and so on. The unit may be applied to any periodic event – for example, a clock might be said to tick at 1 Hz. The reciprocal of frequency is time (period); a frequency of 1 Hz is equivalent to a period of 1 second, a frequency of 1 MHz to a period of 1 microsecond. In older writings, e.g. pre-WWII articles about radio transmissions and its electronics, the older but similar unit cycles per second (cps) is seen, along with related multiples kilocycles, megacycles, and so forth.

SI Multiples

1 kilohertz (symbol kHz) = 10³ Hz = 1,000 Hz

1 megahertz (symbol MHz) = 10⁶ Hz = 1,000,000 Hz

1 gigahertz (symbol GHz) = 10⁹ Hz = 1,000,000,000 Hz

1 terahertz (symbol THz) = 10¹² Hz = 1,000,000,000,000 Hz

1 petahertz (symbol PHz) = 10¹⁵ Hz = 1,000,000,000,000,000 Hz

1 exahertz (symbol EHz) = 10¹⁸ Hz = 1,000,000,000,000,000,000 Hz

Examples

50 or 60 Hz, electromagnetic – standard domestic AC electric power (220V or 110V voltage)
261.626 Hz, acoustic – the musical note middle C
440 Hz, acoustic – concert pitch (A above middle C), used for tuning musical instruments
104 kHz, transitions – the clock speed of the world's first commercial microprocessor, the Intel 4004 (1971)
1–8 MHz, transitions – clock speeds of early home/personal computers (mid-1970s to mid-1980s)
88–108 MHz, electromagnetic – FM radio broadcasts
2.2 GHz, transitions – clock speed of the Pentium 4 microprocessor (2002)
460 THz, electromagnetic – red light
30 PHz, electromagnetic – x-rays