Resonant frequency is where:

• A. Phase is −180°
• B. First peak in magnitude occurs
• C. Bandwidth is max
• D. Gain margin is zero

Answer: (B)

Resonant frequency refers to the specific frequency at which a system naturally oscillates with the greatest amplitude. This phenomenon occurs due to the constructive interference of signals at that particular frequency, resulting in a significant increase in output. In practical terms, for many electronic circuits, particularly in the context of resonant circuits, the resonant frequency is the point where the reactive components (inductance and capacitance) balance each other out, leading to peak voltage and current responses.

At resonant frequency, the circuit exhibits its first peak in magnitude, which can be observed in the frequency response of filters or oscillators. This peak is a clear indicator that energy is being transferred efficiently through the circuit at this frequency, maximizing its output.

Understanding resonance is crucial for designing circuits that require specific frequency responses, such as oscillators and filters used in audio and communication applications. The phenomenon is fundamentally tied to how energy is stored and transferred in reactive components, thus making the first peak in magnitude the key characteristic of resonant frequency.