The flow of electrons in an electric currentThe flow of electrons in an electric current Electrons are tiny particles that are parts of atoms. An electric current is a flow of electrons. Electronics is the study of how electrons behave and how they can be controlled so that they can do useful jobs. Nearly all the machines we use in our everyday lives—computers, phones, TV remote controls, games consoles, calculators, radios, cars and so on—contain electronic circuits that make them work. Electronics are especially important in information technology and telecommunications.

A thermionic triode valve amplifies electric signals.A thermionic triode valve amplifies electric signals.

First electronic devices

The study of electronics began at the end of the 19th century, and had its first practical use in the early 20th century in the development of radio communications. The first electronic devices were called thermionic valves. These included the diode valve, which allowed current to flow through it one way but not the other, and the triode, in which a small current could be used to control a much larger current. The parts of thermionic valves, some of which glowed red hot, had to be enclosed in a glass tube with the air removed to create a vacuum.

Wafers of silicon on a conveyor beltWafers of silicon on a conveyor belt


In the 1950s valves were quickly replaced by more modern electronic components. They were called semiconductor devices because they rely on the properties of semiconductor materials. A semiconductor is a material that can act as both a good conductor of electricity and as an insulator—a material that does not conduct electricity at all. By far the most common semiconductor material is silicon. The flow of an electric current through silicon can be controlled by adding other chemicals to it, or by applying an electric or magnetic field to it, or by exposing it to light or heat. Semiconductor devices are much simpler, smaller and more reliable than valves.


Some electronic componentsSome electronic components


There are dozens of different electronic components, but the most common ones are resistors, capacitors, diodes and transistors. A resistor restricts the flow of current in a circuit. Capacitors store electric charge. Current can flow into them until they are full, and out of them until they are empty. A diode allows current to flow one way but not the other. A transistor can act as a switch or an amplifier. It has three connections. The current flowing between two connections is controlled by a tiny current flowing into the third.

Electronic devicesElectronic devices

Electronic circuits

An electronic circuit is made up of components linked together by wires around which an electric current flows. By combining different components and connecting them in different ways, it is possible to make electronic circuits to carry out almost any job. In an electronic circuit, the components of the circuit itself control the current. For example, in a security light, the electric current is turned on or off by an electronic device that detects whether it is dark and whether anybody is moving nearby.

Modern electronic circuits use integrated circuits, or microchips, in which microscopically small components and the connections between them are built into a wafer of semiconductor material, which is normally silicon.

Consultant: Chris Oxlade


  • 1904
    English engineer John Ambrose Fleming invents the thermionic valve, also known as the vacuum tube. It is a basic device used to alter electronic signal by controlling the flow of electrons.
  • 1907-8
    US engineer Lee De Forest invents the three-electrode vacuum tube, or triode.
  • 1950s
    Thermionic valves are quickly replaced by semiconductor devices.
  • 1958
    The first integrated circuit is built by Texas Instruments in the USA. From this point, the number of components that can fit on a chip increases rapidly.
  • 1971
    The first microprocessor, the Intel 4004, is produced. A microprocessor is the central processing unit (CPU), the main part of a computer, contained on a single chip.

In 1883, US inventor Thomas Edison observed the flow of electrons (not known at the time) from the heated element inside his new incandescent lamp to a cooler metal plate. It was a one-way flow: it did not work in reverse. This effect, called the Edison Effect, was put to use by John Fleming in his invention of the diode valve.

The Audion, the name its inventor Lee De Forest gave to the first triode, was used as a electronic component in early computers. It was also used in long-distance telephones, radio and radar. De Forest came up with his invention by accident: he wasn't sure how it worked.

In 2013 scientists succeeded in making a transistor-like device out of a DNA molecule, the chemical that contains all the body's genes—an "instruction manual" for how the body is built.

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