Electromagnetic waves are energy transported through space in the form of periodic disturbances of electric and magnetic fields. All electromagnetic waves travel through
space at the same speed, c = 2.99792458 x 108 m/s, commonly known as the
speed of light. An electromagnetic wave is characterized by a frequency
and a wavelength. These two quantities are related to the speed of light by the
speed of light = frequency x wavelength
The frequency (and hence, the wavelength) of an electromagnetic wave depends on its
source. There is a wide range of frequency encountered in our physical world, ranging from
the low frequency of the electric waves generated by the power transmission lines to the
very high frequency of the gamma rays originating from the atomic nuclei. This wide
frequency range of electromagnetic waves constitute the Electromagnetic
The Electromagnetic Spectrum
The electromagnetic spectrum can be divided into several wavelength (frequency) regions, among which only a narrow band from about 400 to 700 nm is visible to the human eyes. Note that there is no sharp boundary between these regions. The boundaries shown in the above figures are approximate and there are overlaps between two adjacent regions.
Wavelength units: 1 mm = 1000 µm; 1 µm = 1000 nm.
According to quantum physics, the energy of an electromagnetic wave is quantized, i.e. it can only exist in discrete amount. The basic unit of energy for an electromagnetic wave is called a photon. The energy E of a photon is proportional to the wave frequency f,
E = h f
where the constant of proportionality h is the Planck's Constant,
h = 6.626 x 10-34 J s.
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