# Electrical resistivity

**Electrical resistivity**(also known as

*specific electrical resistance*) is a measure indicating how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electrons.

The resistivity of a material is usually denoted by the lower-case Greek letter rho (ρ); and is given by , where *R* is the resistance of a uniform specimen of the material having a length *l* and a cross-section area *S*. The units of ρ are ohm metres. Its reciprocal quantity is electrical conductivity.

Resistivity can also be defined as , where *E* is the magnitude of the electric field and *J* is the magnitude of the current density.

In general, electrical resistivity of metals increases with temperature, while the resistivity of semiconductors decreases with temperature.

As the temperature of a metal is reduced, the resistance usually reduces until it reaches a constant value, known as the residual resistivity. This value depends not only on the type of metal, but on its purity and thermal history.

Some materials lose all electrical resistivity at sufficiently low temperatures, due to an effect known as superconductivity.

The table of resistivity for various materials (at 20 °C; 10^{-6} Ωm equals Ω·mm²/m):

Material | Resistivity (Ohm-metres) |

Silver | 0.0159 x 10^{-6} |

Copper | 0.017 x 10^{-6} |

Gold | 0.0244 x 10^{-6} |

Aluminum | 0.0282 x 10^{-6} |

Tungsten | 0.056 x 10^{-6} |

Iron | 0.1 x 10^{-6} |

Platinum | 0.11 x 10^{-6} |

Lead | 0.22 x 10^{-6} |

Nichrome (A nickel-chromium alloy commonly used in heating elements) | 1.50 x 10^{-6} |

Carbon | 35 x 10^{-6} |

Germanium | 0.46 |

Silicon | 640 |

Glass | 10^{10} to 10^{14} |

Hard rubber | approximately 10^{13} |

Sulfur | 10^{15} |

Quartz (fused) | 75 x 10^{16} |