What is the greatest instantaneous value of AC called?

The greatest instantaneous value of alternating current (AC) is referred to as the amplitude. Amplitude represents the peak value, which is the highest point of the wave measured from the zero level to the maximum level. This value is important as it indicates the maximum extent of a cycle in a waveform and is crucial for understanding the strength and effectiveness of the AC signal in various applications, such as in power transmission and audio signals.

Frequency refers to how many cycles occur in one second, measured in hertz (Hz), and does not pertain to the magnitude of the wave. Phase indicates the position of a point in time on a waveform cycle and characterizes its displacement but does not measure height or strength. The period is the duration it takes for one complete cycle of the waveform to occur and is inversely related to frequency. Thus, none of these terms adequately describe the peak value of the waveform as amplitude does.