Definition and historical origin of the Hertz unit

Hertz (Hz) is a derived unit of frequency in the SI system. The unit is named after Professor Heinrich Rudolf Hertz, who studied electromagnetic waves.

The name "hertz" was adopted by the CGPM (Conférence générale des poids et mesures) in 1960, replacing the previous name of this unit – cycles per second, along with the corresponding multiples (kilocycles, megacycles, and so on). In common usage, hertz gradually replaced the name cycles per second after 1970.

Hertz in Sound and Light

The hertz unit indicates how many regular events occur in one second. One hertz means one occurrence per second, 100 Hz means one hundred times per second, and so forth.

In relation to sound, the frequency of sound waves determines the pitch. The higher the frequency, the higher the perceived tone. The frequency of sound waves is measured in Hz and typically ranges from 20 Hz to 20,000 Hz.

In relation to light, frequency is used to describe the color of light. The visible spectrum of light consists of different waves with various frequencies corresponding to different colors. For example, red light has a lower frequency than blue light. The frequency of light waves is measured in terahertz (THz), gigahertz (GHz), or megahertz (MHz), and typically ranges from 400 THz to 800 THz for the visible light spectrum.