Assembling circuits that use direct (versus alternating) current requires only a few basic components. The simplest circuit uses three main components: a voltage source, wires to carry current and some sort of resistor. For this introductory lesson, the example circuit will use a battery, resistor, light-emitting diode (LED) and a solderless breadboard that replaces the wires.
The battery is the voltage source, which allows current to flow in the circuit. Ohm's law states that V=IR, where V is voltage in volts, I is current in amperes, and R is resistance measured in ohms. Thus, for a fixed voltage, if resistance increases, the current decreases.
Since voltage sources tend to be available in fixed sizes, such as 1.5 volt or 12 volt batteries, usually the resistance in the circuit is adjusted to obtain an appropriate voltage or current for the application. The resistance is adjusted using a component called a resistor. Resistors are available in an almost infinite variety of sizes and shapes to suit any requirement. In addition, some resistors provide a variable resistance for circuits such as those for dimming lights.
An LED is a special type of diode. Diodes are often used in circuits to ensure that current flows in the correct direction, which prevents damage to circuit components if something is connected wrong. LEDs are special types of diodes that emit light. They are widely used in electronic applications due to their small size and power requirements. Because LEDs only work in one direction, they have both a negative and a positive side that must be connected correctly to work.
The solderless breadboard is a handy device that can be used to quickly build circuits for practice or prototyping. The breadboard has dozens of small holes that connect individual circuit components together using underlying metal surfaces that replace wires and soldering. Most breadboards have two rows of holes on each long edge for attaching power sources and two sets of rows in the middle (with five holes per strip/row being typical) for connecting various devices.
To build a circuit with a breadboard, first build the circuit and then attach the power source. For example, try the following components: a 9 volt battery, a 470 ohm resistor, and an LED that requires about 2 volts to operate. Since the LED only needs 2 volts, the resistor will "step down" the voltage so the LED works correctly. Using the directions for the breadboard, connect one end of the resistor to the + side of the voltage source (without yet connecting the source) and one side to a middle row on the same strip. Connect the LED with the positive side to the same strip and the negative side to the - voltage row. Connect the + and - sides of the power source, and the LED should light.
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