If voltage and current rise and fall at different times, they are said to be what?

When voltage and current rise and fall at different times, they are described as being out of phase. This term indicates that the peaks and troughs of the voltage waveform do not align with those of the current waveform. In alternating current (AC) systems, phase relationships are critical in determining how effectively power is transferred.

If two signals are in phase, they reach their maximum and minimum values simultaneously, leading to maximum power transfer. Conversely, when voltage and current are out of phase, it can result in significant power loss and reduced efficiency in electrical systems. The phase difference can affect how devices operate, influencing factors such as the amount of reactive power in the circuit and the overall efficiency of power delivery.

Understanding phase relationships is fundamental to electrical engineering and AC circuit analysis, as they have important implications for the design and operation of electrical systems.