They store your money. They monitor
your heartbeat. They carry the
sound of your voice into other people's homes. They bring airplanes
into land and guide cars safely to their destination—they even fire off
the airbags if we get into trouble. It's amazing to think just how many
things "they" actually do. "They" are electrons: tiny particles within atoms that march around defined paths known as
circuits carrying electrical energy. One of the greatest things people
learned to do in the 20th century was to use electrons to control
machines and process information. The electronics revolution, as this
is known, accelerated the computer
revolution and both these things have transformed many areas of our
lives. But how exactly do nanoscopically small particles, far too small
to see, achieve things that are so big and dramatic? Let's take a
closer look and find out!
Photo: The compact, electronic circuit board from a webcam.
This board contains several dozen separate electronic components, mostly small resistors and capacitors,
plus the large black microchip (bottom left) that does much of the work.
What's the difference between electricity and electronics?
If you've read our article about electricity,
you'll know it's a kind of energy—a very
versatile kind of energy that we can make in all sorts of ways and use
in many more. Electricity is all about making electromagnetic energy
flow around a circuit so that it will drive something like an electric motor or a heating element,
powering appliances such as electric cars,
kettles, toasters, and
Generally, electrical appliances need a great deal of energy to make
them work so they use quite large (and often quite dangerous) electric
currents. The 2500-watt heating element inside an electric kettle
operates on a current of about 10 amps. By contrast, electronic components use currents
likely to be measured in fractions of milliamps (which are thousandths of amps). In other words, a typical
electric appliance is likely to be using currents tens, hundreds, or thousands
of times bigger than a typical electronic one.
Electronics is a much more subtle kind of electricity in which tiny
electric currents (and, in theory, single electrons) are carefully
directed around much more complex circuits to process signals (such as
those that carry radio and
television programs) or store and process
information. Think of something like a microwave
oven and it's easy to see the difference between ordinary
electricity and electronics. In a microwave, electricity provides the
power that generates high-energy waves that cook your food; electronics
controls the electrical circuit that does the cooking.
Artwork: Microwave ovens are powered by electric cables (gray) that plug into the wall.
The cables supply electricity that powers high-current electrical circuits and low-current electronic ones.
The high-current electrical circuits power the magnetron (blue), the device that makes the waves that cook your food,
and rotate the turntable. The low-current electronic circuits (red) control these high-powered circuits,
and things like the numeric display unit.
Analog and digital electronics
There are two very different ways of storing information—known as
analog and digital. It sounds like quite an abstract idea, but it's
really very simple. Suppose you take an old-fashioned photograph of
someone with a film camera. The camera captures light streaming in
through the shutter at the front as a pattern of light
and dark areas on chemically treated plastic.
The scene you're
photographing is converted into a kind of instant, chemical painting—an
"analogy" of what you're looking at. That's why we say this is an analog
way of storing information. But if you take a photograph of exactly the
same scene with a digital camera,
the camera stores a very different record. Instead of saving a
recognizable pattern of light and dark, it converts the light and dark
areas into numbers and stores those instead. Storing a numerical, coded
version of something is known as digital.
Photo: Analog and digital electronics. The radio (back) is analog: it "soaks" up radio waves and turns them back into sound with electronic components like transistors and capacitors. The camera (front) is digital: it stores and processes photos as numbers.
Electronic equipment generally works on information in either analog
or digital format. In an old-fashioned transistor radio,
broadcast signals enter the radio's circuitry via the antenna sticking
out of the case. These are analog signals: they are radio waves,
traveling through the air from a distant radio transmitter, that
up and down in a pattern that corresponds exactly to the words and
music they carry. So loud rock music means bigger signals than quiet
classical music. The radio keeps the signals in analog form as it
receives them, boosts them, and turns them back into sounds you can
hear. But in a modern digital radio,
things happen in a different way. First, the signals travel in digital
format—as coded numbers. When they arrive at your radio, the numbers
are converted back into sound signals. It's a very different way of
processing information and it has both advantages and disadvantages.
Generally, most modern forms of electronic equipment (including computers, cell
phones, digital cameras, digital radios, hearing aids, and televisions) use
If you've ever looked down on a city from a skyscraper window,
you'll have marveled at all the tiny little buildings beneath you and
the streets linking them together in all sorts of intricate ways. Every
building has a function and the streets, which allow people to travel
from one part of a city to another or visit different buildings in
turn, make all the buildings work together. The collection of
buildings, the way they're arranged, and the many connections between
them is what makes a vibrant city so much more than the sum of its
The circuits inside pieces of electronic equipment are a bit like
cities too: they're packed with components
buildings) that do different jobs and the components are linked
together by cables or printed metal connections
streets). Unlike in a city, where virtually every building is unique
and even two supposedly identical homes or office blocks may be subtly
different, electronic circuits are built up from a small number of
standard components. But, just like LEGO®, you can put these
components together in an infinite number of different places so they
do an infinite number of different jobs.
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.
Photo: A typical resistor on the circuit board from a radio.
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).
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).
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.
Photo: A small capacitor in a transistor radio circuit.
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. (Thyristors are a little bit like transistors, but
work in a different way.)
Photo: A typical field-effect transistor (FET) on an electronic 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.
Electronic components have something very important in common.
Whatever job they do, they work by controlling the flow of electrons
through their structure in a very precise way. Most of these components
are made of solid pieces of partly conducting, partly insulating
materials called semiconductors (described
in more detail in our
article about transistors). Because electronics involves understanding
the precise mechanisms of how solids let electrons pass through them,
it's sometimes known as solid-state physics.
That's why you'll often see pieces of electronic equipment described as "solid-state."
Electronic circuits and circuit boards
The key to an electronic device is not just the components it
contains, but the way they are arranged in circuits. The simplest
possible circuit is a continuous loop connecting two components, like
two beads fastened on the same necklace. Analog electronic appliances
tend to have far simpler circuits than digital ones. A basic transistor
radio might have a few dozen different components and a circuit board
probably no bigger than the cover of a paperback book. But in something
like a computer, which uses digital technology, circuits are much more
dense and complex and include hundreds, thousands, or even millions of
pathways. Generally speaking, the more complex the circuit, the more
intricate the operations it can perform.
Photo: The electronic circuit board from inside a computer printer. Which electronic components
can you see here? I can make out some capacitors, diodes, and integrated circuits (the large black things, which are explained below).
If you've experimented with simple electronics, you'll know that the
easiest way to build a circuit is simply to connect components together
with short lengths of copper cable. But the more components you have to
connect, the harder this becomes. That's why electronics designers
usually opt for a more systematic way of arranging components on what's
called a circuit board. A basic circuit
board is simply a
rectangle of plastic with copper connecting tracks on one side and lots
of holes drilled through it. You can easily connect components together
by poking them through the holes and using the copper to link them
together, removing bits of copper as necessary, and adding extra wires
to make additional connections. This type of circuit board is often
Electronic equipment that you buy in stores takes this idea a step
further using circuit boards that are made automatically in factories.
The exact layout of the circuit is printed chemically onto a plastic
board, with all the copper tracks created automatically during the
manufacturing process. Components are then simply pushed through
pre-drilled holes and fastened into place with a kind of electrically
conducting adhesive known as solder. A circuit manufactured in this way
is known as a printed circuit board (PCB).
Photo: Soldering components into an electronic
circuit. The smoke you can see comes from the solder melting and turning to a vapor. The blue plastic rectangle I'm soldering onto here is a typical printed circuit board—and you see various components sticking up from it, including a bunch of resistors at the front and a large integrated circuit at the top.
Although PCBs are a great advance on hand-wired circuit boards,
they're still quite difficult to use when you need to connect hundreds,
thousands, or even millions of components together. The reason early
computers were so big, power hungry, slow, expensive, and unreliable is
because their components were wired together manually in this
old-fashioned way. In the late 1950s, however, engineers Jack Kilby and
Robert Noyce independently developed a way of creating electronic
components in miniature form on the surface of pieces of silicon. Using
these integrated circuits, it rapidly became
possible to squeeze hundreds, thousands, millions, and then hundreds of millions of
miniaturized components onto chips of silicon about the size of a
finger nail. That's how computers became smaller, cheaper, and much
more reliable from the 1960s onward.
Photo: Miniaturization. There's more computing power
in the processing chip resting on my finger here than you would have found in a room-sized
computer from the 1940s!
What is electronics used for?
Electronics is now so pervasive that it's almost easier to think of
things that don't use it than of things that do.
Entertainment was one of the first areas to benefit, with radio (and
later television) both critically
dependent on the arrival of
electronic components. Although the telephone
was invented before electronics was properly developed, modern
telephone systems, cellphone networks,
and the computers networks at
the heart of the Internet all benefit from
sophisticated, digital electronics.
Try to think of something you do that doesn't involve electronics
and you may struggle. Your car engine
probably has electronic circuits
in it—and what about the GPS satellite
navigation device that tells you where to go? Even the airbag in your
steering wheel is triggered by an electronic circuit that detects when
you need some extra protection.
Electronic equipment saves our lives in other ways too. Hospitals
are packed with all kinds of electronic gadgets, from heart-rate
monitors and ultrasound scanners to complex brain scanners and X-ray
machines. Hearing aids were among the first gadgets to benefit from the
development of tiny transistors in the mid-20th century, and
ever-smaller integrated circuits have allowed hearing aids to become
smaller and more powerful in the decades ever since.
Who'd have thought have electrons—just about the smallest things you
could ever imagine—would change people's lives in so many important
1874: Irish scientist George Johnstone Stoney
(1826–1911) suggests electricity must be "built" out of tiny electrical
charges. He coins the name "electron" about 20 years later.
1875: American scientist George R. Carey
builds a photoelectric cell that makes electricity when light shines on
1879: Englishman Sir William Crookes
(1832–1919) develops his cathode-ray tube (similar to an old-style,
"tube"-based television) to study
electrons (which were then known as "cathode rays").
1883: Prolific American inventor Thomas Edison
(1847–1931) discovers thermionic emission (also known as the Edison
effect), where electrons are given off by a heated filament.
1887: German physicist Heinrich Hertz
(1857–1894) finds out more about the photoelectric effect, the
connection between light and electricity that Carey had stumbled on the
1897: British physicist J.J. Thomson
(1856–1940) shows that cathode rays are negatively charged particles.
Thomson calls them "corpuscles," but they are soon renamed electrons.
1904: John Ambrose Fleming
(1849–1945), an English scientist, produces the Fleming valve (later
renamed the diode). It becomes an indispensable component in radios.
1906: American inventor Lee De Forest
(1873–1961), goes one better and develops an improved valve known as
the triode (or audion), greatly improving the design of radios. De
Forest is often credited as a father of modern radio.
1947: Americans John Bardeen
(1908–1991), Walter Brattain (1902–1987), and
William Shockley (1910–1989)
develop the transistor at Bell Laboratories. It revolutionizes electronics and digital
computers in the second half of the 20th century.
1958: Working independently, American engineers Jack Kilby (1923–2005) of Texas Instruments and
Robert Noyce (1927–1990) of Fairchild
Semiconductor (and later of Intel) develop integrated circuits.
1971: Marcian Edward (Ted) Hoff (1937–)
and Federico Faggin (1941–)
manage to squeeze all the key components of a computer onto
a single chip, producing the world's first general-purpose microprocessor, the Intel 4004.
1987: American scientists Theodore Fulton and Gerald Dolan of Bell Laboratories develop the first single-electron transistor.
2008: Hewlett-Packard researcher Stanley Williams builds the first working memristor, a new
kind of magnetic circuit component that works like a resistor with a memory, first imagined by American physicist Leon Chua almost four decades earlier (in 1971).
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