Define reactance in electrical systems.

Reactance in electrical systems refers specifically to the opposition that inductors and capacitors present to alternating current (AC). This opposition arises not from resistance (which affects both direct current and AC) but rather from the changing nature of AC.

When alternating current flows through a circuit with inductance or capacitance, reactance causes a phase difference between the voltage and current. Inductive reactance increases with frequency and affects how energy is stored and released in the magnetic field of an inductor. Capacitive reactance, on the other hand, decreases with increasing frequency, relating to how energy is stored in an electric field associated with a capacitor.

Understanding reactance is crucial for analyzing AC circuits, as it helps to determine how much power is actually converted to useful work versus how much is reactive power, which does not perform useful work but is essential for the operation of inductive and capacitive components. Thus, option B accurately captures the definition of reactance.