Electronic components

These are some of the most important components you’ll encounter:


These are the simplest components in any circuit. Their job is to restrict the flow of electrons and reduce the current or voltage flowing by converting electrical energy into heat. Resistors come in many different shapes and sizes. Variable resistors (also known as potentiometers) have a dial control on them so they change the amount of resistance when you turn them. Volume controls in audio equipment use variable resistors like these.

Read more in our main article about resistors

Photo: A typical resistor on the circuit board from a radio.

Typical wirewound resistor


The electronic equivalents of one-way streets, diodes allow an electric current to flow through them in only one direction. They are also known as rectifiers. Diodes can be used to change alternating currents (ones flowing back and forth round a circuit, constantly swapping direction) into direct currents (ones that always flow in the same direction).

Read more in our main article about diodes.

Photo: Diodes look similar to resistors but work in a different way and do a completely different job. Unlike a resistor, which can be inserted into a circuit either way around, a diode has to be wired in the right direction (corresponding to the arrow on this circuit board).

Typical diode


These relatively simple components consist of two pieces of conducting material (such as metal) separated by a non-conducting (insulating) material called a dielectric. They are often used as timing devices, but they can transform electrical currents in other ways too. In a radio, one of the most important jobs, tuning into the station you want to listen to, is done by a capacitor.

Read more in our main article about capacitors.

Photo: A small capacitor in a transistor radio circuit.

Small mica capacitor


Easily the most important components in computers, transistors can switch tiny electric currents on and off or amplify them (transform small electric currents into much larger ones). Transistors that work as switches act as the memories in computers, while transistors working as amplifiers boost the volume of sounds in hearing aids. When transistors are connected together, they make devices called logic gates that can carry out very basic forms of decision making.

Read more in our main article about transistors.

Photo: A typical field-effect transistor (FET) on an electronic circuit board.

A FET transistor on a printed circuit board.

Opto-electronic (optical electronic) components

There are various components that can turn light into electricity or vice-versa. Photocells (also known as photoelectric cells) generate tiny electric currents when light falls on them and they’re used as “magic eye” beams in various types of sensing equipment, including some kinds of smoke detector. Light-emitting diodes (LEDs) work in the opposite way, converting small electric currents into light. LEDs are typically used on the instrument panels of stereo equipment. Liquid crystal displays (LCDs), such as those used in flatscreen LCD televisions and laptop computers, are more sophisticated examples of opto-electronics.

Photo: An LED mounted in an electronic circuit. This is one of the LEDs that makes red light inside an optical computer mouse.

LED in closeup

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