What is impedance?

Impedance is defined as the total opposition that a circuit offers to the flow of alternating current (AC). This concept extends beyond mere resistance to include both the resistance (the opposition to the flow of current) and reactance (the opposition due to capacitance and inductance). While resistance is a constant value, reactance can vary with frequency, making impedance a frequency-dependent measurement. In AC circuits, impedance is crucial for understanding how voltage, current, and phase relationships can interact.

The other concepts mentioned, such as the resistance against direct current flow, energy loss in a circuit, or voltage difference across a conductor, do not encapsulate the broader scope of impedance. Resistance pertains specifically to direct current (DC), while energy loss relates to power dissipation and is not a measure of opposition to current flow. The voltage difference across a conductor, on the other hand, describes a different electrical characteristic that involves potential difference rather than the broader opposition to current.