Henry (unit)

Henry
An inductor composed of a wire wound around a magnetic core used to confine and guide the induced magnetic field.
Unit system	SI derived unit
Unit of	Inductance
Symbol	H
Named after	Joseph Henry
In SI base units:	kg⋅m2⋅s−2⋅A−2

The henry (symbol H) is the SI derived unit of electrical inductance. The unit 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 vacuum is 4π × 10⁻⁷ H⋅m⁻¹ (henry per metre).

The inductance of an electric circuit is one henry when an electric current that is changing at one ampere per second results in an electromotive force of one volt across the inductor:

where v(t) denotes the resulting voltage across the circuit, i(t) is the current through the circuit, and L is the inductance of the circuit.

The henry is a derived unit based on four of the seven base units of the International System of Units: kilogram (kg), meter (m), second (s), and ampere (A). Expressed in combinations of SI units, the henry is:

where
Wb = weber,
T = tesla,
J = joule,
m = meter,
s = second,
A = ampere,
V = volt,
C = coulomb,
F = farad,
Hz = hertz,
Ω = ohm