How is impedance defined in AC circuits?

• A. As the resistance to direct current only
• B. As total opposition to current flow, combining resistance and reactance
• C. As the maximum current flow in a circuit
• D. As the average power consumed by the circuit

Answer: (B)

Impedance in AC circuits is defined as the total opposition to current flow, which includes both resistance and reactance. Resistance is the opposition to the flow of current that dissipates energy, while reactance arises from the inductive and capacitive elements of the circuit and is associated with the energy stored in these elements.

In an AC circuit, current and voltage can vary over time, leading to phase differences between them. Impedance not only considers the resistive aspect, which is purely owing to resistors, but also incorporates the effects of inductors and capacitors, which store energy and influence the phase of the current relative to the voltage. The mathematical representation of impedance combines these components, often expressed as a complex number, where the real part represents resistance and the imaginary part represents reactance.

The other choices do not encompass the full concept of impedance in AC circuits. Resistance to direct current only describes a component of the circuit, while maximum current flow pertains to circuit capacity rather than opposition. Average power consumed relates to energy usage over time but does not define impedance itself.