Conductors
Conductors and conductivity  Electrical conductivity of some common materials
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 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/m^{2})
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
Material  Electrical Conductivity  σ  (1/Ω m, S/m, mho/m) 

Aluminum  37.7 10^{6} 
Beryllium  31.3 10^{6} 
Cadmium  13.8 10^{6} 
Calcium  29.8 10^{6} 
Chromium  7.74 10^{6} 
Cobalt  17.2 10^{6} 
Copper  59.6 10^{6} 
Copper  annealed  58.0 10^{6} 
Gallium  6.78 10^{6} 
Gold  45.2 10^{6} 
Iridium  19.7 10^{6} 
Iron  9.93 10^{6} 
Indium  11.6 10^{6} 
Lithium  10.8 10^{6} 
Magnesium  22.6 10^{6} 
Molybdenum  18.7 10^{6} 
Nickel  14.3 10^{6} 
Niobium  6.93 10^{6} 
Osmium  10.9 10^{6} 
Palladium  9.5 10^{6} 
Platinum  9.66 10^{6} 
Potassium  13.9 10^{6} 
Rhenium  5.42 10^{6} 
Rhodium  21.1 10^{6} 
Rubidium  7.79 10^{6} 
Ruthenium  13.7 10^{6} 
Silver  63 10^{6} 
Sodium  21 10^{6} 
Strontium  7.62 10^{6} 
Tantalum  7.61 10^{6} 
Technetium  6.7 10^{6} 
Thallium  6.17 10^{6} 
Thorium  6.53 10^{6} 
Tin  9.17 10^{6} 
Tungsten  18.9 10^{6} 
Zinc  16.6 10^{6} 
Water  Sea  4.5  5.5 
Water  Drinking  0.0005  0.05 
Water  Deionized  5.5 10^{6} 

1 S/m = 10^{4} 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 m^{2}/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 (m^{2})
Example  Resistance of a Wire
The resistance of 1000 m copper wire gauge #10 with cross sectional area 5.26 mm^{2} can be calculated as
R = (1.724 x 10^{8} ohm m^{2}/m) (1000 m) / ((5.26 mm^{2}) (10^{6} m^{2}/mm^{2}))
= 3.2 ohm
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