Resistance, Alternating-Current

(or effective resistance), a quantity characterizing the opposition presented to alternating current by a circuit or part of a circuit owing to the irreversible conversion of electrical energy into other forms of energy, primarily heat. Measured in ohms, AC resistance is equal to the ratio of the active power dissipated in the part of the circuit in question to the square of the effective current in the part. In parts of a circuit that contain conductors of large cross section, the AC resistance is greater than the resistance for direct current because of the skin effect and eddy-current and hysteresis losses in the magnetic field.