Henries

The henry (symbol H) is the SI unit of inductance. Inductance is a property of an electrical circuit that causes an electromotive force to be induced in proportion to the rate of change of current. The defining relation for an inductor with inductance L is ε = −L di/dt, where ε is the induced emf and di/dt is the rate of change of current.

By definition, 1 henry is the inductance of a circuit in which a current changing at 1 ampere per second induces an emf of 1 volt. In base units, 1 H equals 1 kilogram meter squared per second squared per ampere squared (kg·m^2·s^-2·A^-2). The unit is named after Joseph Henry, an American physicist who contributed to the study of electromagnetism in the 19th century. The name was adopted into the metric system as part of the International System of Units.

In practical terms, inductors with inductances ranging from microhenries to henries are used in a wide array of technologies, including filtering, energy storage, and impedance matching in radio frequency circuits and power supplies. The value of inductance depends on the geometry of the conductor, the number of turns in a coil, and the magnetic properties of surrounding materials. Common prefixes (millihenry, microhenry, nanohenry) allow convenient expression of practical values across electronic applications.

The henry is a derived SI unit, closely related to other electrical units through electromagnetic relationships, and is fundamental to the design and analysis of circuits involving time-varying currents.