Magnetic field 'magnetic field' is used to describe as well as or in place of . There are many alternative names for both (see sidebar). In SI units, is measured in teslas (symbol: T) and correspondingly (magnetic flux) is measured in webers (symbol: Wb) so that a flux density of 1 Wb/m is 1 tesla. The SI unit of tesla is equivalent to (newton·second)/(coulomb·metre). In Gaussian-cgs units, is measured in gauss (symbol: G). (The conversion is 1 T = 10000 G.) One nanotesla is equivalent to 1 gamma (symbol: γ). The -field is measured in amperes per metre (A/m) in SI units,
Magnetic flux boundary ∂Σ and, secondly, as the change of magnetic flux through the open surface Σ. This equation is the principle behind an electrical generator. By way of contrast, Gauss's law for electric fields, another of Maxwell's equations, is where Note that the flux of E through a closed surface is "not" always zero; this indicates the presence of "electric monopoles", that is, free positive or negative charges. Magnetic flux In physics, specifically electromagnetism, the magnetic flux (often denoted or ) through a surface is the surface integral of the normal component of the magnetic field B passing through that surface.