What causes fluctuations in a sine wave?

Fluctuations in a sine wave are primarily caused by the presence of harmonics. Harmonics are integer multiples of the fundamental frequency and can introduce additional frequencies into the waveform. When harmonics are present, they can distort the original sine wave, causing it to deviate from its pure form. This distortion results in fluctuations in amplitude and shape of the waveform, which can be perceived as variations or irregularities in the signal.

In practical terms, when analyzing electrical systems or waveforms, harmonics can arise from non-linear loads, such as certain types of electronic devices that draw current in a non-uniform manner. As harmonics are superimposed on the fundamental frequency, they lead to the fluctuations that can affect the performance and efficiency of electrical systems.

Other options typically relate to specific changes in the characteristics of the sine wave but do not primarily cause fluctuations in it. For instance, phase shift refers to a temporal displacement in a wave and would not alter its amplitude but rather its timing. Voltage drop primarily concerns losses in a conductor over distance and does not imply a distortion of the sine wave itself. Frequency variation involves changes to the fundamental frequency, which could alter the waveform, but it is not specifically related to fluctuations in the sine wave.