Final answer:
In an AC circuit, a large lead or lag results in a low power factor, while a zero lead or lag, as seen at resonance, results in a unity power factor.
Step-by-step explanation:
When talking about power factor, when the lead or lag is large, the power factor is low and when the lead or lag is zero, the power factor is unity (or 1). The phase angle between the voltage and current in an AC circuit determines the power factor. At resonance, the current and power factor are both higher, and the power delivered is significantly greater than at other frequencies. If the voltage is lagging the current, a capacitor is typically added to correct the power factor. To achieve a power factor of unity, the reactance of an inductor can be adjusted accordingly.