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| Interactive Tool © phet.colorado.edu |
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Resistivity is a characteristic of a material that varies from one material to another in the same way as they are likely to have different colours, textures & densities. As with calculating the density of a material it is important that the quantity is known in order to make a reliable comparison between materials. In measuring the resistivity of a material it is taken across opposite sides of a cube of the material that has sides of 1m.
This 1m cube of the material is in effect a 1m long conductor that has a CSA of 1m² As 1m equals 1000mm a CSA of 1m² is equal to 1,000,000mm²
The following table shows the resistivity values of a number of commonly used conductors.
| Material | Resistivity (Ρm) at 20 degrees celsius |
|---|---|
| Silver | 16.4×10−9 |
| Copper | 17.5×10−9 |
| Aluminiium | 28.5×10−9 |
| Brass | 75×10−9 |
| Iron | 100×10−9 |
From the above table we can see that the resistivity (resistance across opposite sides of a 1m cube) of copper is 0.0000000175Ω or 0.0175µΩm.
Note that the readings above are very very low values. This is because the length is very short and the CSA is very large compared to conductors we use in the industry.