In wave propagation




For periodic waves in nondispersive media (that is, media in which the wave speed is independent of frequency), frequency has an inverse relationship to the wavelength, λ (lambda). Even in dispersive media, the frequency f of a sinusoidal wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave:

In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes:

When waves from a monochrome source travel from one medium to another, their frequency remains the same—only their wavelength and speed change.

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Definitions

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For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν {\displaystyle \nu } or ν (nu) (see e.g. Planck's formula). The relation between the frequency and the period, T {\displaystyle T} , of a repeating event or oscillation is given by f = 1 T . {\displaystyle f={\frac {1}{T}}.}
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Period versus frequency

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As a matter of convenience, longer and slower waves, such as ocean surface waves, tend to be described by wave period rather than frequency. Short and fast waves, like audio and radio, are usually described by their frequency instead of period. These commonly used conversions are listed below: Frequency 1 mHz (10−3 Hz) 1 Hz (100 Hz) 1 kHz (103 Hz) 1 MHz (106 Hz) 1 GHz (109 Hz) 1 THz (1012 Hz) Period 1 ks (103 s) 1 s (100 s) 1 ms (10−3 s) 1 µs (10−6 s) 1 ns (10−9 s) 1 ps (10−12 s)
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Examples

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Light edit Visible light is an electromagnetic wave, consisting of oscillating electric and magnetic fields traveling through space. The frequency of the wave determines its color: 4 × 1014 Hz is red light, 8 × 1014 Hz is violet light, and between these (in the range 4- 8 × 1014 Hz ) are all the other colors of the visible spectrum. An electromagnetic wave can have a frequency less than 4 × 1014 Hz , but it will be invisible to the human eye; such waves are called infrared (IR) radiation. At even lower frequency, the wave is called a microwave, and at still lower frequencies it is called a radio wave. Likewise, an electromagnetic wave can have a frequency higher than 8 × 1014 Hz , but it will be invisible to the human eye; such waves are called ultraviolet (UV) radiation. Even higher-frequency waves are called X-rays, and higher still are gamma rays. All of these waves, from the lowest-frequency radio waves to the highest-frequency gamma rays, are fundamentally the same, and they are...
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