A periodic but non-sinusoidal wave will produce what kind of spectrum?

A periodic but non-sinusoidal wave is characterized by its repetition over time, but unlike a sinusoidal wave, it does not have a simple smooth waveform. Instead, it can have sharp edges, varying amplitudes, or different shapes, leading to the generation of multiple frequency components when analyzed in the frequency domain.

When performing a Fourier analysis on a periodic non-sinusoidal wave, the result reveals a harmonic spectrum, which consists of the fundamental frequency and its integer multiples—these are referred to as harmonics. This occurs because non-sinusoidal waveforms introduce additional frequency components that are based on integer multiples of the fundamental frequency due to the non-linear nature of their shapes.

Thus, the presence of harmonics in the spectrum is a direct result of this complex waveform, making it the correct choice in this context. The presence of harmonics provides insight into how the waveform interacts with the physical system being observed, and helps in characterizing the different modes of vibration present.