The voltage across the resistor is in phase with the current. The voltage across the inductor leads the current by 90 degrees. The voltage across the capacitor lags the current by 90 degrees. The total voltage across the resistor, inductor and capacitor should be equal to the emf supplied by the generator. . From Figure 2 we can see that .
L depend on frequency.
At this frequency the circuit is said to be at resonance. At resonance the current is in phase with the generator voltage. If we measure voltage across the resistor, depending on frequency, we will obtain a resonance curve of the circuit as shown in Figure 3. If resistance is small and resonance is sharp, the quality factor is large. When the resistor is large, the quality is small.