In a parallel resonant circuit, how does the Q-factor influence the bandwidth around resonance?

• A. Higher Q yields wider bandwidth
• B. Lower Q yields narrower bandwidth
• C. Higher Q yields a narrower bandwidth; Δf ≈ f0 / Q
• D. Q has no effect on bandwidth

Answer: (C)

In a resonant circuit, the Q-factor tells us how sharp the resonance is and how much energy is stored relative to what's lost each cycle. The bandwidth around resonance is tied to this sharpness: a high Q means the circuit responds strongly only in a very narrow frequency range near the resonant frequency. The relationship is Δf ≈ f0 / Q, so increasing Q reduces the bandwidth and makes the resonance narrower. Conversely, lowering Q broadens the peak and widens the bandwidth. This is why a parallel resonant circuit with a higher Q has a narrower bandwidth around the resonance.