ARRL Technician Practice Exam

What is a simple resonant or tuned circuit?

1. A circuit with multiple resistors

2. An inductor and a capacitor connected in series or parallel

3. A capacitor and a diode in series

4. A single resistor connected to a voltage source

The correct answer is: An inductor and a capacitor connected in series or parallel

A simple resonant or tuned circuit primarily consists of an inductor and a capacitor connected together, either in series or parallel. This configuration is fundamental to creating a circuit that can select or "tune" into specific frequencies. When the inductor and capacitor are combined, they form what is known as an LC circuit. The resonance occurs at a particular frequency, which is determined by the values of the inductor and capacitor. At this resonant frequency, the reactance of the inductor and the reactance of the capacitor are equal in magnitude but opposite in phase, allowing the circuit to increase the amplitude of the electrical signal at that frequency significantly. This property makes tuned circuits essential in various applications like radio transmitters and receivers, where selecting and amplifying specific frequencies is crucial. Other options do not constitute a simple resonant or tuned circuit. The presence of multiple resistors does not inherently create resonance, while a capacitor in series with a diode or a single resistor connected to a voltage source does not involve the necessary inductance to achieve resonance. Hence, the combination of an inductor and a capacitor is the defining characteristic of a resonant or tuned circuit.