An electrical circuit is a closed loop formed by a power source, wires, a fuse, a load, and a switch. When the switch is turned on, the electrical circuit is complete and current flows from the negative terminal of the power source, through the wire to the load, to the positive terminal. Any device that consumes the energy flowing through a circuit and converts that energy into work is called a load. A light bulb is one example of a load. It consumes the electricity from a circuit and converts it into work — heat and light.

There are three types of circuits: series circuits, parallel circuits, and series-parallel circuits. A series circuit is the simplest because it has only one possible path that the electrical current may flow. If the electrical circuit is broken, none of the load devices will work. A parallel circuit has more than one path, so if one of the paths is broken, the other paths will continue to work. A series-parallel circuit attaches some of the loads to a series circuit and others to parallel circuits. If the series circuit breaks, none of the loads will function, but if one of the parallel circuits break, that parallel circuit and the series circuit will stop working, but the other parallel circuits will continue to work.

Many "laws" apply to electrical circuits, but Ohm's Law is probably the most well known. Ohm's Law states that an electrical circuit's current is directly proportional to its voltage and inversely proportional to its resistance. So, if voltage increases, for example, the current will also increase, and if resistance increases, current decreases. The formula for Ohm's Law is E = I x R, where E = voltage in volts, I = current in amperes, and R = resistance in ohms.

Source voltage is another important concept in electrical circuits. It refers to the amount of voltage that is applied to the circuit and is produced by the power source. Source voltage is affected by the amount of resistance within the electrical circuit and affects the amount of current. The current is affected by both voltage and resistance. Resistance is not affected by voltage or current, but it affects both voltage and current.