All materials are either conductors or insulators; a material will either conduct electrical current, or impede its flow.

Not all conductors are equally capable of supporting current flow. Copper is a better conductor than nickel. Silver is a better conductor than copper. Gold is a better conductor than Silver. Carbon is a poor conductor.

Similarly, insulators are not perfect. Wood is an insulator if dry, but becomes a conductor when wet. The best insulators are glasses and ceramics. Plastics, such as epoxy, are generally good insulators.

There also are materials that are neither conductors nor insulators. Called “semiconductors,” they are used to make transistors. We will not discuss transistors here, but it is interesting that they are really only resistors that electronic circuits can control. This again shows that Ohms Law is fundamental to circuit design.