Amplitude relates to which aspect of a sound wave?

Amplitude specifically refers to the maximum extent of a vibration or oscillation, which directly correlates to the loudness of a sound wave. In the context of sound waves, greater amplitude means a more significant displacement from the rest position, leading to louder sounds. Conversely, lower amplitude results in quieter sounds. This relationship is crucial because it explains how we perceive sound intensity; a sound wave with a higher amplitude will be heard as louder than one with a lower amplitude.

While frequency relates to the pitch of the sound, wavelength pertains to the distance between consecutive crest or trough points in a wave, and wave speed refers to how quickly the wave travels through a medium, these concepts do not directly define how loud a sound is perceived, which is entirely tied to amplitude. Thus, the correct association of amplitude is indeed with the magnitude of loudness in sound waves.