In physics wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek letter lambda (λ). Examples of wave-like phenomena are light, water waves, and sound waves. The wavelength is related to the frequency by the formula: wavelength = wave speed / frequency. Wavelength is therefore inversely proportional to frequency. Higher frequencies have shorter wavelengths. Lower frequencies have longer wavelengths, assuming the speed of the wave is the same.

Wavelength of a sine wave.

In a wave, properties vary with position. For example, in a sound wave the air pressure oscillates, while in light and other electromagnetic radiation the strength of the electric and the magnetic field vary.

Visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm (430–750 THz). For other examples, see electromagnetic spectrum. The wavelengths of sound frequencies audible to the human ear (20 Hz–20 kHz) are between approximately 17 m and 17 mm, respectively. So the wavelengths in audible sound are much longer than those in visible light.

Speed=wavelengh×frequency

一个正弦波的波长。

在一个波，性质不同的位置。例如，在声波的空气压力振荡，而在光和其他电磁辐射的电场强度和磁场的变化。

可见光的范围从约700 nm，深红色，紫色，约400海里（430–750 THz）。其他的例子，看看电磁频谱。声音的频率，人耳可听的波长（20赫兹–20千赫）约17米和17毫米之间，分别。所以在声音的波长比可见光长。

速度=波长×频率