When alternating voltage and current rise and fall at the same time, what is the power factor?

The power factor is a measure of how effectively electrical power is being converted into useful work output and is defined as the cosine of the phase angle between voltage and current. When alternating voltage and current rise and fall together, they are in phase, meaning that their peaks and troughs occur simultaneously. In this scenario, the phase angle is zero degrees, and the cosine of zero degrees is one.

This condition reflects a power factor of unity, indicating that all the power supplied by the source is being effectively used to do work. In other words, the system is handling power efficiently without any reactive power issues, which is represented by a power factor of 1 (or unity).

In contexts where the voltage and current do not rise and fall together—such as in inductive or capacitive loads—the power factor would deter from unity, potentially resulting in phase differences that can lead to issues such as power loss or inefficiencies in energy transfer.