Henry (unit)

An inductor.

In physics, and electronics, the henry (symbol: H) is the SI unit of inductance. It is named after Joseph Henry (1797-1878), the American scientist who discovered electromagnetic induction independently of and at about the same time as Michael Faraday (1791-1867) in England. The magnetic permeability of the vacuum is 4π×10−7 H/m (henry per metre).

National Institute of Standards and Technology provides guidance for American users of SI to write the plural as henries.

Definition

If the rate of change of current in a circuit is one ampere per second and the resulting electromotive force is one volt, then the inductance of the circuit is one henry.

\mbox{H} = \dfrac{\mbox{m}^2 \cdot \mbox{kg}}{\mbox{s}^{2} \cdot \mbox{A}^2} = \dfrac{\mbox{Wb}}{\mbox{A}} = \dfrac{\mbox{V} \cdot \mbox{s}}{\mbox{A}} = \dfrac{\mbox{J/C} \cdot \mbox{s}}{\mbox{C/s}} = \dfrac{\mbox{J} \cdot \mbox{s}^2}{\mbox{C}^2} = \dfrac{\mbox{m}^2 \cdot \mbox{kg}}{\mbox{C}^2} = \Omega \cdot s

units
A = ampere
V = volt
C = coulomb
J = joule
Wb = weber
kg = kilogram
m = meter
s = second
Ω = ohm

See also

SI units
Base units
Ampere · Candela · Kelvin · Kilogram · Metre · Mole · Second
 SI base unit.svg
Derived units
Becquerel · Coulomb · degree Celsius · Farad · Gray · Henry · Hertz · Joule · Katal · Lumen · Lux · Newton · Ohm · Pascal · Radian · Siemens · Sievert · Steradian · Tesla · Volt · Watt · Weber
Accepted for use
with SI
Atomic mass unit · Astronomical unit · Day · Decibel · Degree of arc · Electronvolt · Hectare · Hour · Litre · Minute · Minute of arc · Neper · Second of arc · Tonne
Atomic units · Natural units
See also
SI prefixes · Systems of measurement · Conversion of units
Wikipedia book Book:International System of Units  · Category Category:SI base units