Henry (unit)

Henry (unit)
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Henry_(unit)".

content

This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (October 2007)

An inductor.

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.

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

units A = amp V = volt C = coulomb J = Joule Wb = weber

SI multiples

SI multiples for henry (H)

Submultiples			Multiples
Value	Symbol	Name	Value	Symbol	Name
10^–1 H	dH	decihenry	10¹ H	daH	decahenry
10^–2 H	cH	centihenry	10² H	hH	hectohenry
10^–3 H	mH	millihenry	10³ H	kH	kilohenry
10^–6 H	µH	microhenry	10⁶ H	MH	megahenry
10^–9 H	nH	nanohenry	10⁹ H	GH	gigahenry
10^–12 H	pH	picohenry	10¹² H	TH	terahenry
10^–15 H	fH	femtohenry	10¹⁵ H	PH	petahenry
10^–18 H	aH	attohenry	10¹⁸ H	EH	exahenry
10^–21 H	zH	zeptohenry	10²¹ H	ZH	zettahenry
10^–24 H	yH	yoctohenry	10²⁴ H	YH	yottahenry

This SI unit is named after Joseph Henry. As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is uppercase (H). When an SI unit is spelled out in English, it should always begin with a lowercase letter (henry), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase.

— Based on The International System of Units, section 5.2.

Since the Greek letter μ caused printing difficulties, the notation uH can be found as a substitute for μH in the electronics literature.

Definition

SI multiples

See also