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In physics, and electronics, the henry (symbol: H) is the SI unit of inductance. Originally the symbol was actually an upside down T but due to the fact no such symbol existed in standard typesets, the symbol was changed to a H. 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.
units
A = ampere
V = volt
C = coulomb
J = joule
Wb = weber
kg = kilogram
m = meter
s = second
Ω = Ohm
SI multiples
| 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 electronics literature.
See also
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