Hz

Hertz (symbol Hz) is the derived SI unit of frequency, defined as one cycle per second. It measures how often a periodic event repeats in time. The unit is named after Heinrich Rudolf Hertz, who demonstrated the existence of electromagnetic waves in the late 19th century. In SI, 1 Hz equals 1 s^-1, reflecting the rate of repeating phenomena such as vibrations, electrical signals, or electromagnetic waves.

Frequency is commonly expressed with metric prefixes: kilohertz (kHz) for thousands of cycles per second, megahertz (MHz) for millions, and gigahertz (GHz) for billions. For very high frequencies, terahertz (THz) is used. In many contexts, the wavelength associated with a frequency f is given by λ = c/f in vacuum, where c is the speed of light; higher frequencies correspond to shorter wavelengths.

In addition to frequency, engineers often use angular frequency ω, measured in radians per second, related to f by ω = 2πf. This distinction is important in wave theory and signal processing, where sinusoidal signals are frequently described by both f and ω.

Hz is applied across disciplines: audio signals are described in hertz (from a few Hz to tens of kHz), radio and microwave communications use MHz to GHz, and optical frequencies reach the terahertz and beyond. The unit provides a concise way to specify the rate of cycles, oscillations, or repeating events in science and technology.