NCEA Level 3 Electricity Practice Test 2025 – Comprehensive Exam Prep

Question: 1 / 400

What unit measures the impedance in an AC circuit?

Volts

Amperes

Ohms

Impedance in an AC circuit is measured in ohms. Impedance, represented by the symbol Z, is a complex quantity that combines resistance and reactance, and it quantifies how much a circuit opposes the flow of alternating current. The unit of impedance, the ohm, is essential for evaluating how much current will flow in relation to the voltage applied, following Ohm's law (V=IZ). Understanding impedance is crucial for analyzing AC circuits, as it determines not just the resistive aspect (like in DC circuits), but also how inductors and capacitors negatively or positively influence the total opposition to current flow at varying frequencies.

In contrast, volts measure electrical potential or voltage, amperes quantify current flow, and hertz represent frequency—none of which provide a measure of impedance specifically. Therefore, ohms is definitively the correct unit used to express impedance in AC circuits.

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