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

• NaOH ₄ - Caustic soda
• NH ₄ Cl - 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
• CuSO ₄ - 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