Which of the following describes a resonant or tuned circuit?

• A. An inductor and a resistor in series
• B. An inductor and a capacitor in series or parallel
• C. A capacitor and a diode in parallel
• D. Two resistors in series

Answer: (B)

A resonant or tuned circuit is characterized by the interaction between inductance and capacitance. This interaction allows the circuit to resonate at a specific frequency, known as the resonant frequency. In the case of an inductor and a capacitor connected either in series or parallel, they create a condition where the reactive effects of the inductor and capacitor counterbalance each other at a particular frequency. At this resonant frequency, the impedance of the circuit is minimized (in series) or maximized (in parallel), which can lead to efficient energy transfer or selective frequency filtering.

This is why an arrangement of an inductor and a capacitor forms the basis of tuned circuits used in various applications, including radio transmitters and receivers. In summary, the presence of both inductive and capacitive elements in a circuit allows for resonance, leading to distinct electrical behaviors not present in circuits composed solely of resistive elements.