Final answer:
When an alternating voltage and current rise and fall at the same time, they are said to be "in phase" and the power factor is 1.
Step-by-step explanation:
The power factor is defined as the amount by which the power delivered in the circuit is less than the theoretical maximum of the circuit due to voltage and current being out of phase. When an alternating voltage and the current that causes it to flow rise and fall at the same time, the two are said to be "in phase" and the power factor is 1.
For example, in a purely resistive circuit, where the impedance equals the resistance, the voltage and current are in phase with each other. This means that the power factor is 1, indicating maximum power delivery to the circuit.
In engineering applications, a high power factor near 1 is desirable as it indicates efficient power delivery.