a material that readily permits the passage of an electric current through it—that is, a material that has a high electrical conductivity, or low resistivity ρ. Good conductors are materials with ρ ≤ 10-6 ohm-cm. In contrast to conductors, insulators have high resistivities—from about 1014 to 1022 ohm-cm. Semiconductors occupy an intermediate position.
Electrical conductivity is determined by the concentration and mobility of the charge carriers. Conductors include metals, electrolytes, and plasmas. In metals, the charge carriers are quasi-free conduction electrons. In electrolytes, the current is produced by positive and negative ions. In a plasma, the current is carried by free electrons and positive and negative ions. At low temperatures, many metals and some semiconductors become superconductors.