How is "resonance" defined in an electrical circuit?

Resonance in an electrical circuit is defined as a condition for maximum current at a specific frequency. This phenomenon occurs in circuits that contain inductance and capacitance, where the inductive and capacitive reactances are equal but opposite in phase, resulting in a significant increase in current flow at that particular frequency.

When the frequency of the applied voltage matches the natural frequency of the circuit, the reactance of the inductor and capacitor cancels each other out, effectively minimizing the overall impedance of the circuit. This leads to an increase in current, assuming the circuit is driven by a voltage source, which is why the correct answer emphasizes the importance of frequency in achieving resonance.

In contrast, conditions like maximum resistance or constant voltage do not accurately describe the resonance effect, nor does decreased impedance alone reflect the current maximization associated with resonance. Thus, understanding how resonance specifically ties to maximum current at an exact frequency is crucial for analyzing and designing resonant circuits effectively.