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Electromagnetic radiation with a wavelength between 380 nm and 760 nm (400–790 terahertz) is detected by the human eye and perceived as visible light. Other wavelengths, especially near infrared (longer than 760 nm) and ultraviolet (shorter than 380 nm) are also sometimes referred to as light, especially when the visibility to humans is not ...
For example, a wavenumber in inverse centimeters can be converted to a frequency expressed in the unit gigahertz by multiplying by 29.979 2458 cm/ns (the speed of light, in centimeters per nanosecond); [5] conversely, an electromagnetic wave at 29.9792458 GHz has a wavelength of 1 cm in free space.
The phase velocity at which electrical signals travel along a transmission line or other cable depends on the construction of the line. Therefore, the wavelength corresponding to a given frequency varies in different types of lines, thus at a given frequency different conductors of the same physical length can have different electrical lengths.
Spatial frequency is a reciprocal length, which can thus be used as a measure of energy, usually of a particle. For example, the reciprocal centimetre, cm −1, is an energy unit equal to the energy of a photon with a wavelength of 1 cm. That energy amounts to approximately 1.24 × 10 −4 eV or 1.986 × 10 −23 J.
ISO 31-6 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to light and related electromagnetic radiations. It is superseded by ISO 80000-7. ISO 31-6 was initially published in 1980, and amended in 1985. It received a revision in 1992, which was amended in 1998.
10 cm = 1.0 dm – wavelength of the highest UHF radio frequency, 3 GHz; 12 cm = 1.2 dm – wavelength of the 2.45 GHz ISM radio band; 21 cm = 2.1 dm – wavelength of the 1.4 GHz hydrogen emission line, a hyperfine transition of the hydrogen atom; 100 cm = 10 dm – wavelength of the lowest UHF radio frequency, 300 MHz
For example, with one point per wavelength of a HeNe reference laser at 0.633 μm (15 800 cm −1) the shortest wavelength would be 1.266 μm (7900 cm −1). Because of aliasing , any energy at shorter wavelengths would be interpreted as coming from longer wavelengths and so has to be minimized optically or electronically.
The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling), is a unit of length in the International System of Units (SI), equal to one billionth (short scale) or one thousand million (long scale) of a meter (0.000000001 m) and to 1000 picometres.