Current density Current density In electromagnetism, current density is the electric current per unit area of cross section. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the charges at this point. In SI units, the electric current density is measured in amperes per square metre. Assume that "A" (SI unit: m) is a small surface centred at a given point "M" and orthogonal to the motion of the charges at "M". If "I" (SI unit: A) is the
History of the metric system the Treaty of the Metre was extended to cover electrical units with the CGPM merging its work with that of the IEC. The twentieth century history of measurement is marked by five periods: the 1901 definition of the coherent MKS system; the intervening 50 years of coexistence of the MKS, cgs and common systems of measures; the 1948 "Practical system of units" prototype of the SI; the introduction of the SI in 1960; and the evolution of the SI in the latter half century. The need for an orthogonal electromagnetic unit to resolve the difficulties of defining such units in