What is a resonant circuit and how does it respond to a specific frequency?

Resonance in a circuit happens when the reactance of the capacitor and the reactance of the inductor cancel each other out at a specific frequency, resulting in a condition where the impedance of the circuit becomes purely resistive. The impedance is the effective opposition to the flow of alternating current and is a combination of resistance, capacitance, and inductance.

The behavior of a resonant circuit can be understood through two main types: series resonant circuit and parallel resonant circuit.

Series Resonant Circuit:

In a series resonant circuit, the inductor (L) and capacitor (C) are connected in series with each other. At the resonant frequency, the reactance of the inductor becomes equal in magnitude but opposite in sign to the reactance of the capacitor. As a result, these reactances cancel each other out, leaving only the resistance (R) as the effective impedance. This leads to a peak in the current flowing through the circuit. The voltage across the components will also be in-phase, and the circuit exhibits minimal opposition to the flow of current.

Parallel Resonant Circuit:

In a parallel resonant circuit, the inductor (L) and capacitor (C) are connected in parallel with each other. At the resonant frequency, the reactance of the inductor and the reactance of the capacitor cancel each other out, leading to a low impedance path for current. As a result, the current flowing through the circuit becomes very high. The voltage across the components will be out of phase, and the circuit exhibits minimal voltage drop.

It's important to note that the resonant frequency is determined by the values of the inductance and capacitance in the circuit. If the frequency of the applied AC signal matches the resonant frequency, the circuit will respond with increased current or voltage amplitude. Frequencies significantly above or below the resonant frequency will result in higher impedance, causing a decrease in current or voltage response.

Resonant circuits have various applications in electronics, including in radio frequency (RF) filters, oscillators, antenna tuning, and impedance matching.