Which of the following is NOT a characteristic of sine waves?

The choice indicating that frequency is constant for all sine waves accurately identifies a fundamental characteristic of sine waves. Sine waves are continuous and periodic signals characterized by a specific frequency that dictates how often the wave cycles occur within a given time frame. Each sine wave can have a different frequency, depending on the context or application, which means it is not correct to generalize that frequency is constant across all sine waves.

In fact, sine waves can represent various frequencies—high, low, or anything in between—depending on the electrical system or the specific parameters at play. Understanding this variability in frequency is crucial when analyzing waveforms in electrical engineering, as it relates to many practical applications, including signal processing and alternating current (AC) power systems.

The other characteristics, such as voltage peaking at 90°, the voltage being zero at certain points, and voltage being expressible in various forms, are accurate representations of how sine waves behave, reinforcing that the statement regarding constant frequency is the most accurate choice for what is not a characteristic applicable to all sine waves.