Henry is the unit used to measure inductance, the reaction of an electric current to changes in the magnetic field that surrounds it. If the flow of current in a circuit changes or alternates, the magnetic field around the circuit also changes. This changing magnetic field induces (creates) a voltage in the circuit that opposes the change in current. A circuit has 1 henry of inductance if a current change of 1 ampere per second induces an opposing voltage of 1 volt. The henry was named after the American physicist Joseph Henry. Its symbol is H.
See also Electric circuit ; Inductance .
