Learning about simple circuits is fundamental to understanding electricity and electronics. Complex circuits can be taken apart and understood as combinations of simple circuits. Computer designers, electricians and radio engineers all need to know the ideas behind simple circuits.
A simple electrical circuit consists of three main elements: a current source wiring, and an electrical load. The current source provides power, wiring carries power to the load, and the load uses the power. Electricity flows in a continuous loop from source to load and back again.
The source of electricity may be a battery, a direct current (DC) power supply, or alternating current (AC) from the power grid. In a simple circuit, the source has two connections, a current source and a return path.
Wiring conducts electricity from the source to the load and back again. Wiring is made of copper or aluminum, and is usually insulated to prevent shocks and short-circuits.
An electrical load consumes electrical energy and does something useful. A load can be a motor, a light bulb, a television or a toaster, for example. The load might not use all the energy the source can provide, but it cannot use more energy than the source provides.
A brief mathematical relationship governs simple circuits. Ohm's Law says, the voltage across a load equals the current through the load times its resistance. If you know any two of these three elements--voltage, current or resistance--the third can be easily determined.