Flux surface surrounding a charge "q" is "q"/ε. In free space the electric displacement is given by the constitutive relation D = ε E, so for any bounding surface the D-field flux equals the charge "Q" within it. Here the expression "flux of" indicates a mathematical operation and, as can be seen, the result is not necessarily a "flow", since nothing actually flows along electric field lines. The magnetic flux density (magnetic field) having the unit Wb/m (Tesla) is denoted by B, and magnetic flux is defined analogously: with the same notation above. The quantity arises in Faraday's law of induction,
Conventional electrical unit not precisely the same as the SI definitions but very nearly equivalent). Conventional electrical units are based on defined values of the Josephson constant and the von Klitzing constant, which allow practical measurements of electromotive force and electrical resistance respectively. Conventional electrical units can be thought of as a scaled version of a system of natural units defined as having consequence: This is a more general (or less specific) version of either the particle physics "natural units" or the quantum chromodynamical system of units but that no unit mass is fixed. Like n.u. or QCD units, with conventional electrical units