Resistivity is a property of a type of material.
It is the general property of a material to resist the flow of electric current.
Its symbol is ρ rho and it is measured in Ωm.
The resistance of a material depends on its dimensions and the material from which it is made.
| Resistance = | resistivity x length
cross-section area |
Resistivity varies with temperature for metals and semiconductors.
The negative temperature coefficient for semiconductors shows that resistivity falls as the temperature increases.
| material | number density at 20°C / m-3 | number density at 50°C / m-3 |
| copper | 8.42 × 1028 | 8.27 × 1028 |
| aluminium | 18.2× 1028 | 17.9× 1028 |
| silicon | 8.49 × 1015 | 7.42 × 1016 |
| germanium | 1.56× 1019 | 6.82 × 1019 |
For metals there is a slight decrease in n due to thermal expansion but this is not significant compared to the increase in collisions.