Ohm between two points of a conductor when a constant potential difference of one volt, applied to these points, produces in the conductor a current of one ampere, the conductor not being the seat of any electromotive force. in which the following units appear: volt (V), ampere (A), siemens (S), watt (W), second (s), farad (F), joule (J), kilogram (kg), metre (m), and coulomb (C). In many cases the resistance of a conductor in ohms is approximately constant within a certain range of voltages, temperatures, and other parameters. These are called linear resistors. In other cases resistance varies (e.g., thermistors). A
Electrical conductor an otherwise-identical short copper wire. The resistance and conductance of a conductor of uniform cross section, therefore, can be computed as where formula_2 is the length of the conductor, measured in metres [m], "A" is the cross-section area of the conductor measured in square metres [m²], σ (sigma) is the electrical conductivity measured in siemens per meter (S·m), and ρ (rho) is the electrical resistivity (also called "specific electrical resistance") of the material, measured in ohm-metres (Ω·m). The resistivity and conductivity are proportionality constants, and therefore depend only on the material the wire is made of, not the geometry of