ARRL Technician Practice Exam

What does the term impedance refer to in an electrical circuit?

1. The total opposition to current flow

2. The measure of voltage

3. The rate of current flow

4. The capacity to store charge

The correct answer is: The total opposition to current flow

Impedance refers to the total opposition that a circuit presents to the flow of alternating current (AC) at a given frequency. This opposition is not just resistance; it also incorporates the effects of capacitive and inductive reactance. In essence, impedance is a complex quantity represented as a combination of resistance (the opposition to current flow that generates heat) and reactance (which includes the effects of inductors and capacitors that store and release energy). Measuring impedance is crucial in various applications, particularly in radio and audio systems, as it affects how signals are transmitted and how efficiently power is used. Understanding impedance helps in designing circuits that perform optimally by ensuring that components match in terms of impedance. The other options relate to different electrical concepts: voltage is a measure of electric potential difference; current flow is quantified as the rate at which charge is flowing, essentially describing the movement of electrons; and the capacity to store charge refers to capacitance, which is related to how much electric charge a capacitor can hold. Each of these plays a role in electrical circuits, but only impedance specifically addresses the total opposition to current flow in the context of AC circuits.