Summary

A conductor is a metallic element that contains fewer than four electrons in its outer shell. An insulator is a non-metallic substance that contains more than four electrons in the outer shell. Semiconductors are a group of materials that cannot be classified either as conductors or insulators; they have exactly four electrons in their outer shell. Current flow is measured by the number of free electrons passing a given point in an electrical circuit per second. Electrical pressure or charge differential is measured in volts, resistance in ohms and current in amperes. If a hydraulic circuit analogy is used to describe an electrical circuit, voltage is equivalent to fluid pressure, current to the flow in gpm, and resistance to flow restriction.

Capacitors are used to store electrons: this consists of conductor plates separated by a dielectric. Capacitance is measured in farads: capacitors are rated by voltage and by capacitance.