Wavelength: The Distance a Wave Travels in One Cycle

The term is wavelength (λ)—the spatial period of a wave: the distance between two consecutive corresponding points (crest to crest, trough to trough, or any identical phase points).

Fundamental Relationship

Wave speed (v) = frequency (f) × wavelength (λ). v = fλ. Higher frequency → shorter wavelength (at constant speed).

Across Wave Types

• Electromagnetic: Radio (km–m), microwave (cm), infrared (µm), visible (400–700 nm), UV, X-ray, gamma (pm).
• Sound (air): 20 Hz → 17 m; 20 kHz → 1.7 cm.
• Water waves: Tsunamis (100+ km), swell (100–200 m), chop (meters).
• Seismic: P-waves (km), S-waves (km).

Measurement

Direct (ruler, laser interferometry) or derived from v = fλ. In dispersive media, wavelength varies with frequency—dispersion relation.

Wavelength is the spatial fingerprint of a wave—defining its interactions with objects (diffraction, resonance, absorption) and its information-carrying capacity.