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The QUALITY FACTOR Q of a series RLC resonant circuit measures
Athe resistance of the circuit
Bthe sharpness of resonance (selectivity)
Cthe maximum current
Dthe source voltage
Answer & Solution
Correct answer: B. the sharpness of resonance (selectivity)
1. Q (Quality factor): $Q = \dfrac{\omega_0 L}{R} = \dfrac{1}{\omega_0 R C} = \dfrac{f_0}{\Delta f}$.
2. HIGH Q: narrow, sharp resonance peak — good for selective filters/tuners.
3. LOW Q: broad, flat response — used in wide-band applications.
4. Bandwidth $\Delta f$ (between -3dB points) is INVERSELY proportional to Q.
5. Q also equals $2\pi$ times the ratio of energy stored to energy lost per cycle.
6. Other options misidentify Q.
_Source: Tony Kuphaldt, "Lessons in Electric Circuits — AC", Vol II, Ch 6 (Q factor in resonance)._
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