ARRL Technician Practice Exam

What is meant by the term impedance?

1. It is a measure of voltage in a circuit

2. It is a measure of the opposition to AC current flow in a circuit

3. It is a measure of energy consumption

4. It is a measure of current in a circuit

The correct answer is: It is a measure of the opposition to AC current flow in a circuit

Impedance is defined as the total opposition that a circuit offers to the flow of alternating current (AC). It combines both resistance (the opposition to current flow in a DC circuit) and reactance (the opposition caused by inductance and capacitance, which varies with frequency). The unit of impedance is ohms, similar to resistance, but it accounts not just for resistive elements but also for how a circuit stores energy through inductance and capacitance during AC conditions. The concept of impedance is crucial in AC circuit analysis, as it helps determine the current flow, voltage drops, and power consumption when alternating currents and voltages are present. Understanding impedance is essential for working with audio and radio frequency circuits, where effective signal transfer and circuit performance rely on managing these reactive components alongside pure resistance.