<P> This SI unit is named after Heinrich Hertz . As with every International System of Units (SI) unit named for a person, the first letter of its symbol is upper case (Hz). However, when an SI unit is spelled out in English, it is treated as a common noun and should always begin with a lower case letter (hertz)--except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using title case . </P> <P> The hertz is named after the German physicist Heinrich Hertz (1857--1894), who made important scientific contributions to the study of electromagnetism . The name was established by the International Electrotechnical Commission (IEC) in 1930 . It was adopted by the General Conference on Weights and Measures (CGPM) (Conférence générale des poids et mesures) in 1960, replacing the previous name for the unit, cycles per second (cps), along with its related multiples, primarily kilocycles per second (kc / s) and megacycles per second (Mc / s), and occasionally kilomegacycles per second (kMc / s). The term cycles per second was largely replaced by hertz by the 1970s . One hobby magazine, Electronics Illustrated, declared their intention to stick with the traditional kc., Mc., etc. units . </P> <P> Sound is a traveling longitudinal wave which is an oscillation of pressure . Humans perceive frequency of sound waves as pitch . Each musical note corresponds to a particular frequency which can be measured in hertz . An infant's ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz; the average adult human can hear sounds between 20 Hz and 16,000 Hz . The range of ultrasound, infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtohertz into the terahertz range and beyond . </P> <P> Electromagnetic radiation is often described by its frequency--the number of oscillations of the perpendicular electric and magnetic fields per second--expressed in hertz . </P>

What does ghz measure in relation to sound