Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

If the conductor in an AC circuit is wound into a coil, what is the term for the opposition to supply voltage?

1. Capacitance

2. Resistance

3. Inductive reactance

4. Magnetic reactance

The correct answer is: Inductive reactance

When a conductor is wound into a coil in an AC circuit, it introduces a property known as inductive reactance. This occurs because the changing current in the coil generates a magnetic field that opposes any change in the current itself, a phenomenon described by Lenz's Law. Inductive reactance is specifically related to the frequency of the alternating current and the inductance of the coil, which is determined by factors such as the number of turns in the coil, the coil's geometry, and the core material used. As the frequency of the AC supply voltage increases, the inductive reactance also increases, resulting in more opposition to the flow of current. This opposition is in addition to any resistance in the circuit, but it's important to distinguish that while resistance is a measure of how much a conductor opposes direct current (DC), inductive reactance is a measure of how it behaves in an AC circuit. Both capacitance and magnetic reactance are different concepts related to capacitive components and the magnetic field effects from AC currents, respectively, and therefore do not correctly describe the opposition faced due to the inductive properties of a coil in an AC circuit.