Conductors

Conductors and conductivity - Electrical conductivity of some common materials

  • Conductors are materials with loosely attached valence electrons - electrons can drift freely between the atoms
  • Insulators have structures where the electrons are bound to the atoms by ionic or covalent bonds - almost no current can flow
  • Semiconductors are insulating materials where the bonds can be broken with applied voltage - electrons can be released and moved from one vacated valence site to another.

Electrical Conductivity

Electrical conductivity or specific conductivity is the measure of a material's ability to conduct electric current. Conductivity is the reciprocal (inverse) of electrical resistivity.

Electrical conductivity is defined as the ratio of the current density to the electric field strength and can be expressed as

 σ = J / E                          (1)

where

σ = electrical conductivity (1/ohms m, 1/Ω m, siemens/m, S/m, mho/m)

J = current density (amps/m2)

E = electric field strength (volts/m)

One siemens - S - is equal to the reciprocal of one ohm and is also referred to as one mho.

Electrical Conductivity of some Common Materials

MaterialElectrical Conductivity
- σ -
(1/Ω m, S/m, mho/m)
Aluminum 37.7 106
Beryllium 31.3 106
Cadmium 13.8 106
Calcium 29.8 106
Chromium 7.74 106
Cobalt 17.2 106
Copper 59.6 106
Copper - annealed 58.0 106
Gallium 6.78 106
Gold 45.2 106
Iridium 19.7 106
Iron 9.93 106
Indium 11.6 106
Lithium 10.8 106
Magnesium 22.6 106
Molybdenum 18.7 106
Nickel 14.3 106
Niobium 6.93 106
Osmium 10.9 106
Palladium 9.5 106
Platinum 9.66 106
Potassium 13.9 106
Rhenium 5.42 106
Rhodium 21.1 106
Rubidium 7.79 106
Ruthenium 13.7 106
Silver 63 106
Sodium 21 106
Strontium 7.62 106
Tantalum 7.61 106
Technetium 6.7 106
Thallium 6.17 106
Thorium 6.53 106
Tin 9.17 106
Tungsten 18.9 106
Zinc 16.6 106
Water - Sea 4.5  - 5.5
Water - Drinking 0.0005 - 0.05
Water - Deionized 5.5 10-6
  • 1 S/m = 104 μS/cm

Electrical Resistivity

Conductivity is the reciprocal (inverse) of electrical resistivity. Electrical resistivity can be expressed as

ρ = 1 / σ   (2)

where 

ρ = electrical resistivity (ohm m2/m, ohm m)

Resistance of a Conductor

The resistance for a conductor can be expressed as

R = ρ l / A   (3)

where

R = resistance (ohms, Ω)

l = length of conductor (m)

A = cross sectional area of conductor (m2)

Example - Resistance of a Wire

The resistance of 1000 m copper wire gauge #10 with cross sectional area 5.26 mm2 can be calculated as

R = (1.724 x 10-8 ohm m2/m) (1000 m) / ((5.26 mm2) (10-6 m2/mm2)) 

   = 3.2 ohm

Related Topics

  • Electrical - Electrical units, amps and electrical wiring, wire gauge and AWG, electrical formulas and motors

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