What is defined as the distance between two nearest points on a wave that are in the same phase?

Wavelength is defined as the distance between two nearest points on a wave that are in the same phase. This means that if you were to look at two consecutive peaks (crests) or troughs of a wave, the distance between these points would represent the wavelength.

In wave mechanics, understanding the wavelength is essential because it is a fundamental characteristic of the wave that relates to its frequency and speed. Wavelength plays a critical role in determining how energy is transmitted through different mediums and is key in various applications, such as telecommunications and acoustics.

The other terms mentioned do not describe this specific distance. For instance, a wave crest refers to the highest point of the wave, amplitude describes the height of the wave from the equilibrium position to the crest or trough, and wave speed refers to how fast the wave is traveling through a medium. Each of these terms captures different aspects of wave behavior, but it is specifically the wavelength that defines the distance between points in the same phase.