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Wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests, or troughs, or corresponding zero crossings as shown.

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats,<ref name=hecht> {{#invoke:citation/CS1|citation |CitationClass=book }}</ref> and the inverse of the spatial frequency. It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns.<ref name=Seaway> {{#invoke:citation/CS1|citation |CitationClass=book }}</ref><ref> {{#invoke:citation/CS1|citation |CitationClass=book }}</ref> Wavelength is commonly designated by the Greek letter lambda (λ). The concept can also be applied to periodic waves of non-sinusoidal shape.<ref name=hecht/><ref name=Flowers> {{#invoke:citation/CS1|citation |CitationClass=book }}</ref> The term wavelength is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.<ref> {{#invoke:citation/CS1|citation |CitationClass=book }}</ref>

Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to frequency of the wave: waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths.<ref> {{#invoke:citation/CS1|citation |CitationClass=book }}</ref>

Wavelength depends on the medium (for example, vacuum, air, or water) that a wave travels through.

Examples of wave-like phenomena are sound waves, light, and water waves. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric and the magnetic field vary. Water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary.

Wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in sinusoidal waves over deep water a particle near the water's surface moves in a circle of the same diameter as the wave height, unrelated to wavelength.<ref name=Pinet> {{#invoke:citation/CS1|citation |CitationClass=book }}</ref> The range of wavelengths or frequencies for wave phenomena is called a spectrum. The name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum.

Wavelength sections
Intro  Sinusoidal waves  More general waveforms  Interference and diffraction  Subwavelength  Angular wavelength  See also  References  External links  

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