Final answer:
The portion of applied power in an AC circuit that produces a magnetic field is known as reactive power, which occurs when the current and voltage are out of phase due to energy storage in the circuit's magnetic or electric fields.
Step-by-step explanation:
The portion of the applied power in an AC circuit that produces a magnetic field is known as reactive power. Unlike active or real power, reactive power does not perform any actual work but is necessary to maintain the electric and magnetic fields in the circuit's inductors and capacitors. Reactive power can be thought of as the energy that is stored in the circuit and then released, rather than used immediately.
For example, in the case of an AC circuit connected to an inductor or a capacitor, reactive power is involved when the current and voltage are out of phase – with the voltage leading the current in an inductor (90° phase angle) and lagging in a capacitor. This phase difference is due to the energy being stored in the magnetic field of the inductor or the electric field of the capacitor.