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In a sine wave, the wavelength is the distance between peaks:
The x axis represents distance, and I would be some varying quantity (for instance air pressure for a sound wave or strength of the electric or magnetic field for light), at a given point in time as a function of x.
Wavelength λ has an inverse relationship to frequency f, the number of peaks to pass a point in a given time. The wavelength is equal to the speed of the wave divided by the frequency of the wave. When dealing with electromagnetic radiation in a vacuum, this speed is the speed of light c, for signals (waves) in air, this is the speed of sound in air. The relationship is given by:
where:
For radio waves this relationship is approximated with the formula: wavelength (in metres) = 300 / frequency (in megahertz).
When light waves (and other electromagnetic waves) enter a medium, their wavelength is multiplied by a factor equal to the refractive indexThe refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. For a non-magnetic material, the square of the refractive index is the material's dielectric const n of the medium, but the frequency of the wave is unchanged. The wavelength of the wave in the medium, λ' is given by:
where λ0 is the vacuum wavelength of the wave. Wavelengths of electromagnetic radiation, no matter what medium they are travelling through, are usually quoted in terms of the vacuum wavelength, although this is not always explicitly stated.
Louis-Victor de Broglie discovered that all particles with momentumIn physics, momentum is a physical quantity related to the velocity and mass of an object. Momentum is the Noether charge of translational invariance. As such, even fields as well as other things can have momentum, not just particles. However, in curved s have a wavelength, called the de Broglie wavelength. For a relativisticSpecial relativity (SR or the special theory of relativity is the physical theory published in 1905 by Albert Einstein. It replaced Newtonian notions of space and time, and incorporated electromagnetism as represented by Maxwell's equations. The theory is particle, this wavelength is given bywhere h is the Planck constant, p is the particle's momentum, m is the particle's mass, and v is the particle's velocity.
The greater the energy, the larger the frequency and the shorter (smaller) the wavelength. Given the relationship between wavelength and frequency, it follows that short wavelengths are more energetic than long wavelengths.
See also: frequency, period, amplitude
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