Hertz (Hz)

Hertz is the SI unit of frequency, defined as one cycle per second. It is named after physicist Heinrich Hertz and applies universally to periodic phenomena such as sound waves, electromagnetic radiation, and oscillating systems.

Frequency and Time Period

Frequency f is the reciprocal of the time period T of one complete cycle:

f = 1 / T

where:

• f: Frequency in hertz (Hz)

• T: Time period in seconds (s)

Frequency, Wavelength, and Wave Velocity

For wave-based systems, frequency relates to wavelength λ and wave velocity v by:

f = v / λ

where:

• v: Wave velocity in m/s (e.g., the speed of light c for EM waves)

• λ: Wavelength in meters (m)

SI Prefixes for Frequency

Frequency values are often expressed using SI prefixes:

• 1 kHz = 1,000 Hz

• 1 MHz = 1,000,000 Hz

• 1 GHz = 1,000,000,000 Hz

• 1 THz = 1,000,000,000,000 Hz

Examples in Practice

• Power grids: 50 Hz (Europe, Asia), 60 Hz (North America)

• Audio range: Human hearing spans roughly 20 Hz to 20,000 Hz

• Visible light: Frequencies range from approx. 430 THz to 750 THz

Applications

Hertz is fundamental in a wide range of fields:

• Telecommunications: Frequency bands define AM/FM, cellular, and satellite systems

• Computing: CPU clock rates measured in GHz

• Audio engineering: Frequency analysis for reproduction and tuning

• Power systems: Grid stability depends on frequency control

• Quantum physics: Atomic transition frequencies define modern timekeeping