# Resistivity, Conductivity and Temperature Coefficients for common Materials

## Resistivity, conductivity and temperature coefficients for some common materials as silver, gold, platinum, iron and more - Including a tutorial explanation of resistivity and conductivity

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The factor in the resistance which takes into account the nature of the material is the resistivity.

Resistivity is the

- resistance of a unit cube of the material measured between the opposite faces of the cube

Material | Resistivity Coefficient ^{2) }- ρ - (ohm m^{2}/m)( Ω m) | Temperature Coefficient ^{2)} (per degree C)(1/ ^{o}C) | Conductivity - σ - (1 /(Ω m)) |
---|---|---|---|

Aluminum | 2.65 x 10^{-8} | 3.8 x 10^{-3} | 3.77 x 10^{7} |

Animal fat | 14 x 10^{-2} | ||

Animal muscle | 0.35 | ||

Antimony | 41.8 x 10^{-8} | ||

Barium (0^{o}C) | 30.2 x 10^{-8} | ||

Beryllium | 4.0 x 10^{-8} | ||

Bismuth | 115 x 10^{-8} | ||

Brass - 58% Cu | 5.9 x 10^{-8} | 1.5 x 10^{-3} | |

Brass - 63% Cu | 7.1 x 10^{-8} | 1.5 x 10^{-3} | |

Cadmium | 7.4 x 10^{-8} | ||

Caesium (0^{o}C) | 18.8 x 10^{-8} | ||

Calcium (0^{o}C) | 3.11 x 10^{-8} | ||

Carbon (graphite)^{1)} | 3 - 60 x 10^{-5} | -4.8 x 10^{-4} | |

Cast iron | 100 x 10^{-8} | ||

Cerium (0^{o}C) | 73 x 10^{-8} | ||

Chromel (alloy of chromium and aluminum) | 0.58 x 10^{-3} | ||

Chromium | 13 x 10^{-8} | ||

Cobalt | 9 x 10^{-8} | ||

Constantan | 49 x 10^{-8} | 3 x 10^{-5} | 0.20 x 10^{7} |

Copper | 1.724 x 10^{-8} | 4.29 x 10^{-3} | 5.95 x 10^{7} |

Dysprosium (0^{o}C) | 89 x 10^{-8} | ||

Erbium (0^{o}C) | 81 x 10^{-8} | ||

Eureka | 0.1 x 10^{-3} | ||

Europium (0^{o}C) | 89 x 10^{-8} | ||

Gadolium | 126 x 10^{-8} | ||

Gallium (1.1K) | 13.6 x 10^{-8} | ||

Germanium^{1)} | 1 - 500 x 10^{-3} | -50 x 10^{-3} | |

Glass | 1 - 10000 x 10^{9} | 10^{-12} | |

Gold | 2.24 x 10^{-8} | ||

Graphite | 800 x 10^{-8} | -2.0 x 10^{-4} | |

Hafnium (0.35K) | 30.4 x 10^{-8} | ||

Holmium (0^{o}C) | 90 x 10^{-8} | ||

Indium (3.35K) | 8 x 10^{-8} | ||

Iridium | 5.3 x 10^{-8} | ||

Iron | 9.71 x 10^{-8} | 6.41 x 10^{-3} | 1.03 x 10^{7} |

Lanthanum (4.71K) | 54 x 10^{-8} | ||

Lead | 20.6 x 10^{-8} | 0.45 x 10^{7} | |

Lithium | 9.28 x 10^{-8} | ||

Lutetium | 54 x 10^{-8} | ||

Magnesium | 4.45 x 10^{-8} | ||

Manganese | 185 x 10^{-8} | 1.0 x 10^{-5} | |

Mercury | 98.4 x 10^{-8} | 8.9 x 10^{-3} | 0.10 x 10^{7} |

Mica (Glimmer) | 1 x 10^{13} | ||

Mild steel | 15 x 10^{-8} | 6.6 x 10^{-3} | |

Molybdenum | 5.2 x 10^{-8} | ||

Neodymium | 61 x 10^{-8} | ||

Nichrome (alloy of nickel and chromium) | 100 - 150 x 10^{-8} | 0.40 x 10^{-3} | |

Nickel | 6.85 x 10^{-8} | 6.41 x 10^{-3} | |

Nickeline | 50 x 10^{-8} | 2.3 x 10^{-4} | |

Niobium (Columbium) | 13 x 10^{-8} | ||

Osmium | 9 x 10^{-8} | ||

Palladium | 10.5 x 10^{-8} | ||

Phosphorus | 1 x 10^{12} | ||

Platinum | 10.5 x 10^{-8} | 3.93 x 10^{-3} | 0.943 x 10^{7} |

Plutonium | 141.4 x 10^{-8} | ||

Polonium | 40 x 10^{-8} | ||

Potassium | 7.01 x 10^{-8} | ||

Praseodymium | 65 x 10^{-8} | ||

Promethium | 50 x 10^{-8} | ||

Protactinium (1.4K) | 17.7 x 10^{-8} | ||

Quartz (fused) | 7.5 x 10^{17} | ||

Rhenium (1.7K) | 17.2 x 10^{-8} | ||

Rhodium | 4.6 x 10^{-8} | ||

Rubber - hard | 1 - 100 x 10^{13} | ||

Rubidium | 11.5 x 10^{-8} | ||

Ruthenium (0.49K) | 11.5 x 10^{-8} | ||

Samarium | 91.4 x 10^{-8} | ||

Scandium | 50.5 x 10^{-8} | ||

Selenium | 12.0 x 10^{-8} | ||

Silicon^{1)} | 0.1-60 | -70 x 10^{-3} | |

Silver | 1.59 x 10^{-8} | 6.1 x 10^{-3} | 6.29 x 10^{7} |

Sodium | 4.2 x 10^{-8} | ||

Soil, typical ground | 10^{-2} - 10^{-4} | ||

Solder | 15 x 10^{-8} | ||

Stainless steel | 10^{6} | ||

Strontium | 12.3 x 10^{-8} | ||

Sulfur | 1 x 10^{17} | ||

Tantalum | 12.4 x 10^{-8} | ||

Terbium | 113 x 10^{-8} | ||

Thallium (2.37K) | 15 x 10^{-8} | ||

Thorium | 18 x 10^{-8} | ||

Thulium | 67 x 10^{-8} | ||

Tin | 11.0 x 10^{-8} | 4.2 x 10^{-3} | |

Titanium | 43 x 10^{-8} | ||

Tungsten | 5.65 x 10^{-8} | 4.5 x 10^{-3} | 1.79 x 10^{7} |

Uranium | 30 x 10^{-8} | ||

Vanadium | 25 x 10^{-8} | ||

Water, distilled | 10^{-4} | ||

Water, fresh | 10^{-2} | ||

Water, salt | 4 | ||

Ytterbium | 27.7 x 10^{-8} | ||

Yttrium | 55 x 10^{-8} | ||

Zinc | 5.92 x 10^{-8} | 3.7 x 10^{-3} | |

Zirconium (0.55K) | 38.8 x 10^{-8} |

^{1)} Note! - the resistivity depends strongly on the presence of impurities in the material.

^{2}^{)} Note! - the resistivity depends strongly on the temperature of the material. The table above is based on 20^{o}C reference.

### Electrical Resistance in a Wire

The electrical resistance of a wire is greater for a longer wire and less for a wire of larger cross sectional area. The resistance depend on the material of which it is made and can be expressed as:

R = ρ L / A(1)

where

R= resistance (ohm,Ω)

ρ= resistivity coefficient (ohm m, Ω m)

L= length of wire (m)

A= cross sectional area of wire (m^{2})

The factor in the resistance which takes into account the nature of the material is the resistivity. Since it is temperature dependent, it can be used to calculate the resistance of a wire of given geometry at different temperatures.

The inverse of resistivity is called conductivity and can be expressed as:

σ = 1 / ρ(2)

where

σ= conductivity (1 / Ω m)

#### Example - Resistance in an Aluminum Cable

Resistance of an aluminum cable with length *10 m* and cross sectional area of *3 mm ^{2}* can be calculated as

*R = (2.65 10 ^{-8} Ω m) (10 m) / ((3 mm^{2}) (10^{-6} m^{2}/mm^{2}))*

* = 0.09 Ω*

### Resistance

The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current which flows through it:

R = V / I(3)

where

R= resistance (ohm)

V= voltage (V)

I= current (A)

### Ohm's Law

If the resistance is constant over a considerable range of voltage, then Ohm's law,

I = V / R(4)

can be used to predict the behavior of the material.

### Resistance and Temperature

For most materials the electrical resistance increases with temperature. Change in resistance can be expressed as

dR / R_{s}= α dT(5)

where

dR= change in resistance (ohm)

R_{s}= standard resistance according reference tables (ohm)

α= temperature coefficient of resistance ()^{o}C^{-1}

dT= change in temperature from reference temperature (^{o}C, K)

(5) can be modified to:

*dR = α dT R _{s} (5b)*

The "temperature coefficient of resistance" - *α** *- of a material is the increase in the resistance of a *1 Ω* resistor of that material when the temperature is increased *1 ^{o}C*.

#### Example - Resistance of a Copper wire in Hot Weather

A copper wire with resistance *0.5 Ω* at normal operating temperature *20 ^{o}C* is in hot sunny weather heated to

*80*. The temperature coefficient for copper is

^{o}C*4.29 x 10*and the change in resistance can be calculated as

^{-3}(1/^{o}C)*dR = ( 4.29 x 10^{-3} 1/^{o}C) ((80 ^{o}C) - (20 ^{o}C)) (0.5 kΩ)*

* = 0.13 (kΩ)*

The resulting resistance for the copper wire in hot weather will be

*R = (0.5 kΩ) + (0.13 kΩ) *

* = 0.63 (kΩ) *

* = 630 (Ω)*

#### Example - Resistance of a Carbon resistor when Temperature is changed

A carbon resistor with resistance *1 kΩ* at temperature *20 ^{o}C* is heated to

*120*. The temperature coefficient for carbon is negative

^{o}C*-4.8 x 10*- the resistance is reduced with increasing temperature.

^{-4}(1/^{o}C)The change in resistance can be calculated as

*dR = ( -4.8 x 10^{-4} 1/^{o}C) ((120 ^{o}C) - (20 ^{o}C)) (1 kΩ)*

* = - 0.048 (kΩ)*

The resulting resistance for the resistor will be

*R = (1 kΩ) - (0.048 kΩ) *

* = 0.952 (kΩ) *

* = 952 (Ω)*

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