Electric current electrons into the conduction band. The current-carrying electrons in the conduction band are known as "free electrons", though they are often simply called "electrons" if that is clear in context. Current density is a measure of the density of an electric current. It is defined as a vector whose magnitude is the electric current per cross-sectional area. In SI units, the current density is measured in amperes per square metre. where "formula_6" is current in the conductor, formula_7 is the current density, and formula_8 is the differential cross-sectional area vector. The current density (current per unit area) "formula_7" in materials
Electrical resistivity and conductivity is the driving consideration. Electrical resistivity and conductivity Electrical resistivity (also known as specific electrical resistance, or volume resistivity) is a fundamental property of a material that quantifies how strongly that material opposes the flow of electric current. A low resistivity indicates a material that readily allows the flow of electric current. Resistivity is commonly represented by the Greek letter "ρ" (rho). The SI unit of electrical resistivity is the ohm-metre (Ω⋅m). As an example, if a solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is 1 Ω, then the resistivity