The measure between two crests of a wave is called the "wavelength." Wavelength is a fundamental property of a wave and is defined as the distance between two consecutive points that are in phase, meaning they have the same displacement and are moving in the same direction. In the case of a typical sinusoidal wave (like a sound wave or a water wave), the wavelength is the distance between two adjacent crests or two adjacent troughs.
In symbols, the wavelength is represented by the Greek letter lambda (λ). The relationship between wavelength (λ), wave speed (v), and frequency (f) is given by the wave equation:
v = λ * f
where: v = wave speed (in meters per second, m/s) λ = wavelength (in meters, m) f = frequency (in hertz, Hz)
In this equation, the wave speed is the speed at which the wave propagates through a medium (e.g., the speed of sound in air or the speed of light in a vacuum), and frequency represents the number of oscillations (cycles) of the wave per unit time.
As a simple example, if a sound wave has a frequency of 440 Hz (common pitch for the musical note A4) and the wave speed is approximately 343 meters per second (speed of sound in air at room temperature), we can find the wavelength:
v = 343 m/s (speed of sound in air) f = 440 Hz (frequency of the sound wave)
λ = v / f λ = 343 m/s / 440 Hz ≈ 0.779 meters
So, in this example, the wavelength of the sound wave is approximately 0.779 meters, or 779 millimeters, which is the distance between two adjacent crests of the wave.