Electronics Engineering (ELEX) Board Practice Exam

In a series RLC circuit driven by an AC signal generator, what causes the current to undergo resonance?

1. Voltage amplitude

2. Supply frequency

3. Capacitance value

4. Inductance value

The correct answer is: Supply frequency

The phenomenon of resonance in a series RLC circuit is fundamentally linked to the supply frequency. When the frequency of the AC signal from the generator matches the natural frequency of the RLC circuit, resonance occurs. At this point, the inductive and capacitive reactances cancel each other out, resulting in a condition where the impedance of the circuit is minimized to just the resistance (R). This means that the circuit can draw maximum current from the voltage source. The frequency at which this occurs is determined by the values of the inductance (L) and capacitance (C) in the circuit, specifically calculated by the formula \( f_0 = \frac{1}{2\pi\sqrt{LC}} \). Thus, when the supply frequency aligns with this natural frequency, resonance is achieved, leading to a significant increase in current flow in the circuit. While the values of capacitance and inductance also play a role in determining the resonant frequency, it is ultimately the supply frequency that triggers the actual resonance phenomenon by matching this calculated frequency. Therefore, the supply frequency is crucial in causing resonance in a series RLC circuit.