In contrast to the constant one-way flow of direct current, alternating current changes direction many times each second. Electricity is delivered from power stations to customers as AC because it provides a more efficient way to transport electricity over long distances.

Current is the rate of flow of electrons per unit time and is measured in amperes (A). A coulomb (C) is the quantity of electricity conveyed in one second by a current of one ampere.

An inductor is coiled wire that stores electric energy in the form of magnetic energy and resists changes in the electric current flowing through it. If current is increasing, the inductor produces a voltage that slows the increase and, if current is decreasing, the magnetic energy in the coil opposes the decrease to keep the current flowing longer. In contrast to capacitors, inductors allow DC to pass easily but resist the flow of AC.

Ohm's law specifies the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit: V = IR.

A closed circuit is a complete loop or path that electricity follows. It consists of a source of voltage, a load, and connective conductors. If the circuit is interrupted, if a wire is disconnected or cut for example, it becomes an open circuit and no electricity will flow.