Table of Contents
What Is Wavelength?
Wavelength is the distance between successive crests (or troughs) of a wave. It is inversely proportional to frequency: higher frequency means shorter wavelength. For electromagnetic waves in vacuum, the speed is always the speed of light (299,792,458 m/s), making wavelength and frequency directly interchangeable.
Wavelength determines many physical properties: the color of visible light, the pitch of sound, the penetrating power of radiation, and the antenna size needed for radio reception. It is measured in meters, but nanometers (nm) are common for light, and angstroms for X-rays.
The Wave Equation
Where λ is wavelength (m), v is wave speed (m/s), and f is frequency (Hz). For light in vacuum, v = c = 299,792,458 m/s. For sound in air at 20°C, v = 343 m/s.
Electromagnetic Spectrum Wavelengths
| Type | Wavelength Range | Frequency Range |
|---|---|---|
| Radio | 1 mm - 100 km | 3 kHz - 300 GHz |
| Microwave | 1 mm - 1 m | 300 MHz - 300 GHz |
| Infrared | 700 nm - 1 mm | 300 GHz - 430 THz |
| Visible Light | 380 - 700 nm | 430 - 790 THz |
| Ultraviolet | 10 - 380 nm | 790 THz - 30 PHz |
| X-rays | 0.01 - 10 nm | 30 PHz - 30 EHz |
Types of Waves
- Electromagnetic: Travel at the speed of light in vacuum; include radio, light, and X-rays.
- Sound: Mechanical waves; speed depends on medium (343 m/s in air, 1480 m/s in water).
- Water waves: Surface waves with speed dependent on depth and wavelength.
- Seismic: Travel through Earth; P-waves at 5-8 km/s, S-waves at 3-4.5 km/s.
Frequently Asked Questions
What is the wavelength of visible light?
Visible light ranges from about 380 nm (violet) to 700 nm (red). Green light, to which human eyes are most sensitive, is around 555 nm. Each color corresponds to a specific wavelength range.
Does wavelength change in different media?
Yes. When light enters a denser medium like glass or water, it slows down, and its wavelength decreases proportionally. Frequency remains constant. This is why light bends (refracts) at interfaces between media.
How is wavelength related to energy?
For photons, energy E = hc/λ, where h is Planck's constant. Shorter wavelength means higher energy. This is why UV light causes sunburn but visible light does not, and why gamma rays are dangerous.