Sine Wave:

In its purest form, alternating current has a sinusoidal, or sine-wave, nature. The waveform in figure shown below is a sine wave. Any ac wave which consists of a single frequency has a perfect sine-wave shape. Any ideal sine-wave current holds one and only one component frequency.

In practice, a wave can be too close to a sine wave which it looks precisely like the sine function on an oscilloscope whenever in reality there are traces of other frequencies present. Imperfections are frequently too small to see. Utility ac in the United States has a nearly perfect sine-wave shape, with a frequency of 60 Hz. Though, there are small aberrations.

Figure: A sine wave. The period is the length of time needed for one cycle to be completed.