- Materials can be separated into two categories based on how well they conduct electricity. Good conductive materials are called conductors. Materials with low conductivity are called insulators. Most metals are conductors. Rusts on metals, however, are insulators. Water is a conductor. Plastic and rubber are two kinds of insulators. Wood is usually an insulator, although it can conduct charges if they are large enough.
- It takes an electric field to get the electrons in a material to move. One way of measuring conductivity is by measuring the ratio of the strength of the electric current to the strength of the electric field producing it. If more current is produced by a smaller field in one material than in another, then that material is said to have more conductivity. This measure of conductivity is named "Siemens per meter."
- Another way of measuring conductivity is by "percent IACS." IACS stands for International Annealed Copper Standard. Copper is one of the best conductors, which is why wires are usually made of copper. Percent IACS is a description of a material's conductivity by comparing it with copper's conductivity. A material that is 50 percent IACS conducts half as well as copper.
- The conductivity of any material changes with the temperature of that material. Most measurements of conductivity are made at 20 degrees Celsius as a standard. As the temperature increases, the conductivity decreases. This is because hot atoms vibrate more and interfere with the movement of the electrons. At high enough temperatures some materials can stop functioning as conductors and become insulators.
- The measurement of electrical conductivity has many uses. It is of course useful for determining what materials to make electrical parts out of. It is used to determine the purity of water, as water's conductivity changes when it is impure. It can be used to check that metals have been properly heat-treated and also to sort materials by type automatically.
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