What is the term for the combination of resistance and reactance that restricts the flow of alternating current?

The term for the combination of resistance and reactance that restricts the flow of alternating current is impedance. Impedance extends the concept of resistance to AC circuits, incorporating not only the actual resistance to current flow but also the effects of reactance, which stems from capacitors and inductors. This means that impedance reflects how much the circuit opposes the current flow in an AC system, taking into account both the resistive and reactive components.

Capacitance specifically refers to the ability of a component to store electrical energy in an electric field, which is not directly related to the overall opposition to current flow in AC circuits. Reactance, while a component of impedance, only accounts for the opposition due to capacitors and inductors, not the resistive component. Resistance alone measures the opposition to current in a DC circuit and does not provide a complete picture in the context of AC. Hence, the most comprehensive term that encompasses all of these factors together in AC circuits is impedance.