Perfect Conductor

A perfect conductor is an electrical conductor with no resistivity. The concept is used to model systems in which the electrical resistance or resistivity is negligible compared to other effects. One such model is ideal magnetohydrodynamics, the study of perfectly conductive fluids. Another example is electrical circuit diagrams, which carry the implicit assumption that the wires connecting the components have no resistance.

All known materials that are perfectly conductive also happen to be superconductors. The latter, in addition to having no electrical resistance, exhibit quantum effects such as the Meissner effect and quantization of magnetic flux through closed loops. The property of perfect conductance, together with the law of electromagnetic induction, requires that the magnetic field inside a perfect conductor remain fixed, but according to classical electrodynamics it could have a nonzero, eternal value. In real superconductors, all magnetic flux is expelled during the phase transition to superconductivity, and the magnetic field is zero within the bulk of the superconductor (the Meissner effect).

A perfect conductor without the special quantum properties of real superconductors is known as a classical superconductor, but that phrase is ambiguous as it is also used in some communities to distinguish between conventional superconductors and high-temperature superconductors. No such materials are known to exist, though the concept is a useful idealization of the low-resistivity case in many systems.