How is impedance defined in an AC circuit?

Impedance in an AC circuit is a crucial concept that encompasses not just resistance but also the effects of inductance and capacitance. Specifically, impedance is defined as the combined effect of resistance (the opposition to current flow in the circuit) and reactance (which arises from inductors and capacitors). Reactance itself includes both inductive reactance, which opposes changes in current flow due to inductors, and capacitive reactance, which opposes changes in voltage due to capacitors.

This comprehensive definition reflects the nature of AC circuits, where both resistance and reactance impact the relationship between current and voltage. The impedance is usually represented as a complex number, allowing both the magnitude and phase angle to be expressed—this distinguishes it from mere resistance, which is a purely real value.

Understanding impedance is essential for analyzing AC circuitry because it directly affects how voltage and current behave with time-varying signals. In essence, it integrates all forms of opposition that the circuit presents to alternating current, thereby determining factors like power consumption and phase relationships between current and voltage.

The other options do not accurately capture this multi-faceted nature of impedance. While current and voltage, resistance, and their ratios are important in circuit analysis, they do not fully represent