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Published online by Cambridge University Press: 30 November 2009
Electromagnetic radiation
Besides what is commonly called light, electromagnetic radiation includes radiation of longer (infrared, microwave) and shorter (ultraviolet, X-ray) wavelengths (see p. xvii). As the name implies electromagnetic (EM) radiation contains both electric field E and magnetic field B components. The use of the bold typeface indicates that these are vector quantities. The relationship between the electric and magnetic fields is best illustrated by considering plane-polarized radiation. Here the electric vector is confined to a single plane. Figure B.1 depicts such radiation of wavelength λ travelling with phase velocity c (the velocity at which the crests of the wave travel) in a vacuum (c = 2.998 × 108 m s-1) along the x-axis. The electric component of the radiation is in the form of an oscillating electric field and the magnetic component is an oscillating magnetic field. These fields are orthogonal and are also at right angles to the direction of propagation of the radiation. The plane of polarization is conventionally taken to be the plane containing the direction of the electric field. Unpolarized radiation, or radiation of an arbitrary polarization, can always be resolved into two orthogonally polarized waves. If the two electric field components possess a constant phase difference and equal amplitudes, the resultant EM wave is said to be circularly polarized.
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