In power factor calculations, what would happen if voltage and current are in phase?

When voltage and current are in phase, it means that the peaks of the voltage wave coincide with the peaks of the current wave, and similarly for the troughs. This situation indicates that all the power supplied by the source is being used effectively by the load without any reactive power component, which occurs in purely resistive circuits.

In such a case, the power factor, which is defined as the cosine of the phase angle between voltage and current, will equal one. This is because in-phase conditions correspond to a phase angle of zero degrees, and the cosine of zero degrees is one. A power factor of one signifies that the circuit is operating at maximum efficiency, with no phase shift resulting in wasted energy. Thus, when voltage and current are in phase, the power factor indeed equals one, reflecting an efficient transfer of real power.

A power factor of less than one indicates some degree of reactive power in the system, while a power factor greater than one is not physically possible in conventional AC systems. Saying the power factor becomes irrelevant doesn't accurately capture the importance of knowing whether the system operates efficiently under varying loads.