What is the definition of impedance in an AC circuit?

Impedance in an AC circuit is defined as the total opposition to the flow of alternating current. This concept extends beyond just resistance, as it incorporates both resistance and reactance, which accounts for the effects of inductors and capacitors in the circuit. Reactance can vary with frequency, making impedance frequency-dependent. Thus, impedance is a comprehensive measure that represents how much the circuit resists the flow of AC, combining the resistive elements with the reactive elements into a single value typically expressed in ohms.

The other options focus on different aspects of electrical concepts. The ratio of voltage to current describes the concept of resistance but does not encompass reactance, which is a critical part of impedance in AC circuits. The resistance of the conducting path is only one component of impedance; it neglects the effects of reactive components that impact AC flow. Lastly, the phase difference between voltage and current relates to how AC voltage and current can be out of sync but is not a direct measure of the opposition to current flow itself. Thus, understanding impedance as the total opposition to AC flow provides a clearer picture of how these elements work together in an AC circuit.