10.3: Conductivity of Some Common Materials
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The values below are conductivity \(\sigma\) for a few materials that are commonly encountered in electrical engineering applications, and for which conductivity emerges as a consideration.
Note that materials in some applications are described instead in terms of resistivity , which is simply the reciprocal of conductivity.
Conductivity may vary significantly as a function of frequency. The values below are representative of frequencies from a few kHz to a few GHz. Conductivity also varies as a function of temperature. In applications where precise values are required, primary references accounting for frequency and temperature should be consulted. The values presented here are gathered from a variety of references, including those indicated in “Additional References” at the end of this section.
Free Space (vacuum): \(\sigma\triangleq 0\).
| Material | \(\sigma\) (S/m) |
|---|---|
| Copper | \(5.8\times 10^7\) |
| Gold | \(4.4\times 10^7\) |
| Aluminum | \(3.7\times 10^7\) |
| Iron | \(1.0\times 10^7\) |
| Platinum | \(0.9\times 10^7\) |
| Carbon | \(1.3\times 10^5\) |
| Silicon | \(4.4\times 10^{-4}\) |
Water exhibits \(\sigma\) ranging from about \(6~\mu\)S/m for highly distilled water (thus, a very poor conductor) to about \(5\) S/m for seawater (thus, a relatively good conductor), varying also with temperature and pressure. Tap water is typically in the range 5–50 mS/m, depending on the level of impurities present.
Soil typically exhibits \(\sigma\) in the range \(10^{-4}\) S/m for dry soil to about \(10^{-1}\) S/m for wet soil, varying also due to chemical composition.
Non-conductors . Most other materials that are not well-described as conductors or semiconductors and are dry exhibit \(\sigma < 10^{-12}\) S/m. Most materials that are considered to be insulators , including air and common dielectrics, exhibit \(\sigma < 10^{-15}\) S/m, often by several orders of magnitude.