Q.How will you define Q-factor ?

Q-factor measures the sharpness of resonance in a series LCR circuit — the ratio of the voltage magnification across $L$ (or $C$) at resonance to the applied voltage, $Q=\omega_0 L/R$.

Definition

In a series LCR resonant circuit, the Quality factor (Q-factor) is defined as the ratio of the voltage developed across the inductor (or across the capacitor) at resonance to the applied (source) voltage:

$Q = \dfrac{\text{Voltage across } L\ (\text{or } C)\ \text{at resonance}}{\text{Applied voltage}}$

At resonance, the angular frequency is $\omega_0 = \dfrac{1}{\sqrt{LC}}$, and the Q-factor can be written as

$Q = \dfrac{\omega_0 L}{R} = \dfrac{1}{\omega_0 CR} = \dfrac{1}{R}\sqrt{\dfrac{L}{C}}$

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