Electrical Conductivity - Elements and other 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

• 1 S/m = 10⁴ μS/cm = mho/m

• 1 S/cm = 10^-2 S/m

• 1 1/Ω m = S/m = 3.28 1/Ω ft = 3.28 S/ft

Electrical Conductivity of Elements relative to Silver

Electrical Conductivity of Highly Purified Water

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

Resistivity and Conductivity Conversion

• grains/gal = 17.1 ppm CaCO₃

Electrical Conductivity of Aqueous Solutions

Electrical conductivity of aqueous solutions like

• NaOH₄ - Caustic soda
• NH₄Cl - Ammonium chloride, Sal ammoniac
• NaCl₂ - Common salt
• NaNO₃ - Sodium nitrate, Chilean saltpetre
• CaCl₂ - Calcium chloride
• ZnCl₂ - Zinc chloride
• NaHCO₃ - Sodium bicarconate, baking soda
• Na₂CO₃ - Sodium carbonate, soda ash
• CuSO₄ - Copper sulfate, blue vitriol

Temperature ^oC
K
^oF

Length m
km
in
ft
yards
miles
naut miles

Area m²
km²
in²
ft²
miles²
acres

Volume m³
liters
in³
ft³
us gal

Weight kg_f
N
lbf

Velocity m/s
km/h
ft/min
ft/s
mph
knots

Pressure Pa
bar
mm H₂O
kg/cm²
psi
inches H₂O

Flow m³/s
m³/h
US gpm
cfm