What does a wave's amplitude indicate?

A wave's amplitude is a measure of the maximum displacement of points on a wave from its rest position. In the context of waves, particularly those that carry energy, such as sound waves or electromagnetic waves, the amplitude is directly related to the energy transported by the wave. Higher amplitude means that the wave carries more energy, while lower amplitude signifies that the energy is less. This principle is evident in various wave phenomena; for example, louder sounds correspond to greater amplitudes of sound waves.

The other options refer to different characteristics of waves: frequency indicates how many wave cycles occur in a unit of time, speed refers to how fast the wave travels through a medium, and wavelength is the distance between consecutive points of the same phase in the wave, such as crest to crest. Each of these characteristics is distinct from amplitude and represent different aspects of wave behavior.