Electromagnetic radiation and B fields in EMR are in-phase (see math section below). An important aspect of light's nature is its frequency. The frequency of a wave is its rate of oscillation and is measured in hertz, the SI unit of frequency, where one hertz is equal to one oscillation per second. Light usually has multiple frequencies that sum to form the resultant wave. Different frequencies undergo different angles of refraction, a phenomenon known as dispersion. A wave consists of successive troughs and crests, and the distance between two adjacent crests or troughs is called the wavelength. Waves of the electromagnetic spectrum
Madelung constant Madelung constant allows for the calculation of the electric potential "V" of all ions of the lattice felt by the ion at position "r" where "r" =|"r" - "r"| is the distance between the "i"th and the "j"th ion. In addition, If the distances "r" are normalized to the nearest neighbor distance "r" the potential may be written with formula_3 being the (dimensionless) Madelung constant of the "i"th ion The electrostatic energy of the ion at site formula_5 then is the product of its charge with the potential acting at its site There occur as many Madelung constants formula_3 in