View source for Electrical resistivity and conductivity

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'''Electrical resistivity''' (also called specific '''electrical resistance''' or '''volume resistivity''') is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows electric current. Resistivity is commonly represented by the Greek letter '''ρ''' (rho). The SI unit of electrical resistivity is the ohm-meter (Ω⋅m). For example, if a 1 m<sup>3</sup> solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is 1 Ω, then the resistivity of the material is 1 Ω⋅m.

'''Electrical conductivity''' or '''specific conductance''' is the reciprocal of electrical resistivity. It represents a material's ability to conduct electric current. It is commonly signified by the Greek letter '''σ''' (sigma), but '''κ''' (kappa) (especially in electrical engineering) and '''γ''' (gamma) are sometimes used. The SI unit of electrical conductivity is siemens per metre (S/m).

The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In classical (that is, non-superconducting) conductors, such as [[copper]] or [[silver]], this decrease is limited by impurities and other defects. Even near absolute zero, a real sample of a normal conductor shows some resistance. In materials displaying [[superconductivity]] however, the resistance drops abruptly to zero when the material is cooled below its critical temperature. In a normal conductor, the current is driven by a voltage gradient, whereas in a superconductor, there is no voltage gradient and the current is instead related to the phase gradient of the superconducting order parameter. A consequence of this is that an electric current flowing in a loop of superconducting wire can persist indefinitely with no power source.

==References==
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===Relevant Sciencemadness threads===
*[https://www.sciencemadness.org/whisper/viewthread.php?tid=1390 Conductivity of distilled water]
*[http://www.sciencemadness.org/talk/viewthread.php?tid=5064 Electrical Conductivity of Energetic Materials]
*[https://www.sciencemadness.org/whisper/viewthread.php?tid=66122 Building a Heating Element?]

[[Category:Concepts]]