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

Which of the following is NOT considered a factor in determining impedance in an AC circuit?

1. Resistance

2. Reactance

3. Frequency

4. Voltage

The correct answer is: Frequency

In an AC circuit, impedance is a measure of how much the circuit resists the flow of electric current and is determined by both resistance and reactance. While resistance refers to the opposition to current flow from resistors, reactance stems from inductors and capacitors and reflects the opposition that they provide based on the frequency of the AC signal. The key factors influencing impedance are resistance, which is constant, and reactance, which varies with the frequency of the AC signal. Frequency plays a critical role since the reactance of inductors and capacitors changes with different frequencies. Higher frequencies may increase inductive reactance and decrease capacitive reactance, thereby affecting the total impedance experienced in the circuit. Voltage, while crucial for circuit operation, does not directly influence the impedance itself. Instead, it is a result of the relationship between current and impedance. Therefore, since voltage does not factor into the calculation of impedance like resistance, reactance, and frequency do, it is correct to state that voltage is not a determining factor in the impedance of an AC circuit.