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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).
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.
SI multiples for henry (H)
This SI unit is named after Joseph Henry. As with all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (H). But when an SI unit is spelled out, it should always be written in lowercase (henry), unless it begins a sentence or is the name "degree Celsius".
— Based on The International System of Units, section 5.2.