CREST
A
X
The crest.
Usually the Greek letter Lambda.
CREST
crest
A
X
The crest.
Usually the Greek letter Lambda.
The loudness of a sound (or intensity) corresponds to the sound wave's amplitude. The amplitude of a wave is the distance from the midpoint of the wave to a high-point (crest) or low-point (trough).
crest
The distance from crest to crest in a transverse wave is called a wavelength.
Wave Length
It's not an idiom. It means just what it says -- something is on the crest of a wave. The crest is the top of the wave.
In a wave, it is called the wave length.