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Conductors and Insulators
To conduct an electric current is the same as to transmit electrons. All substances have some ability to transmit electrons but they differ greatly in the ease with which electrons pass through them. For instance, a copper wire conducts electricity readily; glass seems to conduct so little current that it is hardly measurable. Substances through which currents easily pass are known to be conductors. Those substances that strongly resist the flow of current are termed insulators. An insulator is also called a dielectric. It has very few free charges that are able to move under the influence of the electric field.
There is, however, no sharp distinction between conductors and insulators (dielectrics). Under ordinary conditions there is no perfect conductor and no perfect dielectrics. For instance, paper though a poor conductor is by no means a perfect insulator. All substances conduct a little electricity — even such materials as porcelain, rub-ber, paper, and glass, which are considered as good insula¬tors. However, the insulators have so few electrons that can move about freely that, in practice, they don’t allow a current to flow through them.
Almost all metals are good conductors of electricity but silver is believed to be the best conductor of all. Copper comes next; it is followed by aluminum. Copper is our most commonly used conductor. In addition to its high con¬ductivity, copper is abundant, easily mined and processed.
Some liquids also conduct electric currents. They even prove to be good conductors of electricity.
Most gases conduct current under proper conditions of pressure and temperature. They are not as good electrical conductors as metals.
