When might a capacitor be used in a motor circuit?

In motor circuits, a capacitor is primarily used to improve power factor, which is the correct answer. The power factor represents the ratio of real power flowing to the load to the apparent power in the circuit. In inductive loads, such as motors, power factor tends to be low because these devices draw reactive power. When capacitors are added to the circuit, they provide leading reactive power, which can counteract the lagging reactive power produced by the inductive load. This helps to align the current and voltage waveforms more closely, thereby improving the overall power factor of the system, reducing energy losses, and enhancing system efficiency.

The other options, while they address potential functions of other components or circuit configurations, do not accurately reflect the primary function of a capacitor in this context. Reducing current draw typically relates more to the motor's design or the use of variable frequency drives. Limiting voltage spikes is often managed with surge protectors or snubber circuits rather than capacitors alone. Synchronizing phases generally applies to specific applications involving multiple motors or systems running in parallel, which requires more complex controls beyond just the addition of a capacitor.