Electrical Impedance

Opposition that a circuit presents to electric current. It includes both resistance and reactance. Resistance arises from collisions of the current-carrying charged particles with the internal structure of the conductor.

Reactance is an additional opposition to the movement of electric charge that arises from the changing electric and magnetic fields in circuits carrying alternating current. Impedance in circuits carrying steady direct currents is simply resistance. The magnitude of the impedance &math.Z; of a circuit is equal to the maximum value of the potential difference, or voltage &math.V;, across the circuit, divided by the maximum value of the current &math.I; through the circuit, or simply &math.Z; = &math.V;/&math.I;. The unit of impedance is the ohm.