单项选择题 The power factor is a measure of the phase difference between voltage and current and is expressed as the（） of the phase angle.

单项选择题 With a purely resistance load the voltage and current are in phase, giving a power factor of （）.

单项选择题 The alternating current generator supplying a load has a voltage drop resulted from the loadWhen the load has a lagging power factor this voltage drop （）.