What is an RLC circuit?

• A. A circuit that contains a resistor, inductor, and capacitor connected in either series or parallel.
• B. A circuit that contains only a capacitor.
• C. A circuit with a transformer and capacitor.
• D. A circuit containing an inductor and capacitor only.

Answer: (A)

An RLC circuit is a circuit that contains a resistor, an inductor, and a capacitor, connected in series or in parallel. The resistor provides energy loss and sets the overall damping, while the inductor and capacitor store energy in magnetic and electric fields and interact with each other as reactive elements. In a series configuration, the total impedance is Z = R + j(ωL − 1/ωC); at the resonant frequency ω0 = 1/√(LC) the reactive parts cancel, leaving the resistance as the main component of the impedance, so current is maximized. In a parallel configuration, the admittances add, and at resonance the circuit can present a very high impedance. These interactions make RLC circuits versatile for tuning and filtering, with common uses in band-pass, low-pass, or high-pass filters and in impedance matching.

The other options don’t fit because they omit one or more of the required components: a circuit with only a capacitor isn’t an RLC circuit; a transformer with a capacitor isn’t describing an RLC network; and a circuit with an inductor and capacitor only lacks the resistor, which makes it an LC (not RLC) circuit.