Electrical conductivity
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Electrical conductivity is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current. The conductivity σ is defined as the ratio of the current density <math>\mathbf{J}</math> to the electric field strength <math>\mathbf{E}</math>:
- <math>\mathbf{J} = \sigma \mathbf{E}</math>.
It is also possible to have materials in which the conductivity is anisotropic, in which case σ is a 3×3 matrix (or more technically a rank-2 tensor) which is generally symmetric.
Conductivity is the reciprocal (inverse) of electrical resistivity, and has the SI units of siemens per metre (S·m-1). It is commonly represented by the Greek letter σ, but κ or γ are also occasionally used.
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Classification of materials by conductivity
Scientists often divide materials into three classes based upon their respective conductivities:
- A conductor such as a metal has high conductivity.
- An insulator like glass or a vacuum has low conductivity.
- The conductivity of a semiconductor is generally intermediate, but varies widely under different conditions, such as exposure of the material to electric fields or certain frequencies of light.
Some typical electrical conductivities
| Electrical Conductivity (S·m-1) | Temperature(°C) | Notes | |
|---|---|---|---|
| Silver | 63.01 × 106 | 20 | Highest electrical conductivity of any metal |
| Copper | 59.6 × 106 | 20 | |
| Aluminium | 37.8 × 106 | 20 | |
| Sea water | 5 | ||
| Drinking water | 0.0005 – 0.05 | ||
| Ultra pure water | 5.5 × 10-6 |
Complex conductivity
To analyse the conductivity of materials exposed to alternating electric fields, it is necessary to treat conductivity as a complex number (or as a matrix of complex numbers, in the case of anisotropic materials mentioned above) called the admittivity. This method is used in applications such as electrical impedance tomography, a type of industrial and medical imaging. Admittivity is the sum of a real component called the conductivity and an imaginary component called the susceptivity. [1]
See also
- electrical conduction for a discussion of the physical origin of electrical conductivity.
- electrical resistance
- electrical resistivity is the inverse of electric conductivity
- SI electromagnetism unitsbg:Специфична електропроводимост
ca:Conductivitat elèctrica cs:Elektrická vodivost da:Elektrisk ledningsevne de:Elektrische Leitfähigkeit es:Conductancia eléctrica fa:رسانایی fi:Sähkönjohtavuus fr:Conductivité électrique he:מוליכות חשמלית it:Conduttività elettrica nl:Elektrische geleidbaarheid pl:Konduktywność pt:Condutividade elétrica ro:Conductibilitate electrică ru:Электрическая проводимость sl:Električna prevodnost sv:Konduktivitet sr:Специфична електрична проводљивост