How is "frequency" defined in electrical systems?

Frequency in electrical systems is defined as the number of cycles per second of alternating current (AC), which is measured in hertz (Hz). This definition highlights how often the AC waveform completes one full cycle - from one peak to the next - within a second.

Understanding frequency is crucial because it determines how electrical devices operate and interact with the power supply. For instance, in many countries, the standard power line frequency is either 50 Hz or 60 Hz, which affects the efficiency and performance of various appliances and machinery.

The other choices do not accurately reflect the definition of frequency. The power produced per cycle is related to energy transfer but does not convey the concept of frequency. The number of cycles per day does not provide a measure of temporal frequency, as it lacks the critical time aspect of how many cycles occur in one second. Lastly, the change in voltage over time relates to the concept of voltage dynamic behavior but does not define frequency itself.