Wind turbines

Wind turbines are like airplanes running on the spot—spinning round but going nowhere. They're serving a very useful purpose, however. There's energy locked in wind and these giant propellers can capture some of it and turn it instantly into electricity. Have you ever stopped to wonder how wind turbines work? Let's take a closer look!

Photo: Left: A small wind farm in Colorado, United States. These are relatively small turbines: each one produces about 700kW of energy (enough to supply 225 homes). The turbines are 79m (260ft) high (from the ground to the very top of the rotors) and the rotors themselves are 48.5m (159ft) in diameter. The top part of each turbine (called the nacelle) rotates on the tower beneath so the spinning blades are always facing directly into the wind. Photo by Warren Gretz courtesy of US Department of Energy/NREL (DoE/NREL).

How does a turbine generate electricity?

A turbine is a machine that spins around in a moving fluid (liquid or gas) and catches some of the energy passing by. All sorts of machines use turbines, from jet engines to hydroelectric power plants and from diesel railroad locomotives to windmills. Even a child's toy windmill is a simple form of turbine.

The huge rotor blades (propellers) on the front of a wind turbine are the "turbine" part. As wind passes by, the kinetic energy (energy of movement) it contains makes the blades spin around (usually quite slowly). The blades have a special curved shape so they capture as much energy from the wind as possible.

Although we talk about "wind turbines," the turbine is only one of the three main parts inside these giant machines. The second part is a gearbox whose gears convert the slow speed of the spinning blades into higher-speed rotary motion—turning the drive shaft quickly enough to power the electricity generator.

The generator is the third main part of a turbine and it's exactly like an enormous, scaled-up version of the dynamo on a bicycle. When you ride a bicycle, the dynamo touching the back wheel spins around and generates enough electricity to make a lamp light up. The same thing happens in a wind turbine, only the "dynamo" generator is driven by the turbine's rotor blades instead of by a bicycle wheel, and the "lamp" is a light in someone's home dozens of miles away. Read more in our main article about generators.

Photo: Head for heights! You can see just how big a wind turbine is compared to this engineer, who's standing right inside the nacelle (main unit) carrying out maintenance. Notice how the white blades at the front connect via an axle (gray—under the engineer's feet) to the gearbox and generator behind (blue). Photo by Lance Cheung courtesy of US Air Force.

How does a wind turbine work?

1. Wind (moving air that contains kinetic energy) blows toward the turbine's rotor blades.
2. The rotors spin around slowly, capturing some of the kinetic energy from the wind, and turning the central drive shaft that supports them.
3. The rotor blades can swivel on the hub at the front so they meet the wind at the best angle for harvesting energy.
4. Inside the nacelle (the main body of the turbine sitting on top of the tower and behind the blades), the gearbox converts the low-speed rotation of the drive shaft (about 16 revolutions per minute, rpm) into high-speed (1600 rpm) rotation fast enough to drive the generator efficiently.
5. The generator, immediately behind the gearbox, takes kinetic energy from the spinning drive shaft and turns it into electrical energy.
6. Anemometers (wind-speed monitors) and wind vanes on the back of the nacelle provide measurements about the wind speed and direction.
7. Using these measurements, the entire top part of the turbine (the rotors and nacelle) can be rotated by a yaw motor, mounted between the nacelle and the tower, so it faces directly into the oncoming wind and captures the maximum amount of energy. If the wind speed rises too much, brakes are applied to stop the rotors from turning (for safety reasons).
8. The electric current produced by the generator flows through a cable running down through the inside of the turbine tower.
9. A substation transforms the voltage of the electricity so it can be transmitted efficiently to nearby communities.
10. Homes enjoy clean, green energy.
11. Wind carries on blowing past the turbine, but with lower speed and lower energy (for reasons explained below) and more turbulence (since the turbine has disrupted its flow).

How turbines harvest maximum energy

If you've ever seen a wind turbine, you'll know that they are absolutely gigantic and mounted on incredibly high towers. The bigger the rotor blades, the more energy they can capture from the wind. The giant blades (typically 70 m or 230 feet in diameter, which is about 30 times the wingspan of an eagle) multiply the wind's force like a wheel and axle, so even a gentle breeze is enough to make the outer edges of the blades turn around. Although the blades rotate quite slowly, the inner axle and turbine rotate with greater force—enough to turn the generator and make electricity. (Wind turbines usually have anemometers—automatic speed measuring devices—built into them and brakes that lock the blades if the wind speed is too high.)

A typical wind turbines is 85 meters (280 feet) off the ground—that's like 50 tall adults standing on one another's shoulders! There's a good reason for this. If you've ever stood on a hill that's the tallest point for miles around, you'll know that wind travels much faster when it's clear of the buildings, trees, hills, and other obstructions at ground level. So if you put a turbine's rotor blades high in the air, they capture considerably more wind energy than they would lower down. And capturing energy is what wind turbines are all about.

Photo: This unusual Darrieus "egg-beater" wind turbine rotates about a vertical axis, unlike a normal propeller turbine. Its main advantage is that it can be mounted nearer to the ground, without a tower, which makes it cheaper and simpler to construct. Photo by courtesy of US Department of Energy.

Since the blades of a wind turbine are rotating, they must have kinetic energy, which they "steal" from the wind. Now it's a basic law of physics (known as theconservation of energy) that you can't make energy out of nothing, so the wind must actually slow down slightly when it passes around a wind turbine. That's not really a problem, because there's usually plenty more wind following on behind! It is a problem if you want to build a wind farm: unless you're in a really windy place, you have to make sure each turbine is a good distance from the ones around it so it's not affected by them.

Advantages and disadvantages of wind turbines

One of the drawbacks of wind turbines is that they don't generate anything like as much energy as a conventional power plant. Each turbine makes about 1 megawatt of power, which is enough to power 500 electric toasters running simultaneously—and enough to supply about 1000 homes. You'd need about 1000–2000 turbines to make as much power as a really sizable coal-fired power plantor a nuclear power station (either of which can generate enough power to run a million toasters at the same time). But on the plus side, wind turbines are clean and green: unlike coal stations, they don't make the carbon dioxide emissions that are causing global warming or the sulfur dioxide emissions that cause acid rain. And they don't have the security and pollution problems many people associate with nuclear power. Is wind the energy of the future? It just might be!

But what if the wind doesn't blow?

It's hard to imagine why anyone would object to clean and green wind turbines—especially when you compare them to dirty coal-fired plants and risky nuclear ones. Some people worry that because wind is very variable, we might suddenly lose all our electricity and find ourselves plunged into a "blackout" (a major power outage) if we rely on it too much.

The reality of wind is quite different. Wherever you live, your power comes from a complex grid (network) of highly interconnected power-generating units (ranging from giant power plants to individual wind turbines). Utility companies are highly adept at balancing power generated in many different places, in many different ways, to match the load (the total power demand) as it varies from hour to hour and day to day. The power from any one wind turbine will fluctuate as the wind rises and falls, but the total power produced by thousands of turbines, widely dispersed across an entire country, is much more regular and predictable. For a country like the UK, it's pretty much always windy somewhere. As Graham Sinden of Oxford University's Environmental Change Institute has shown, low wind speeds affect more than half the country for only 10 percent of the time; for 60 percent of the time, only 20 percent of the UK suffers from low wind speeds; and only for one hour per year is 90 percent of the UK suffering low speeds (Sinden 2007, figure 7). In other words, having many wind turbines spread across many different places guarantees a reasonably steady supply of wind energy virtually all year round.

While it's true that you might need 1000 wind turbines to produce as much power as a giant coal or nuclear plant, it's also true that if a single wind turbine fails or stops turning, it causes only 1/1000th (0.1 percent) of the disruption you get when a coal or nuclear plant fails (which happens more often than you might think). It's also worth bearing in mind that wind is extremely predictable several days in advance so it's easy for power planners to take account of its variability as they figure out how to make enough power to meet expected demands.

Opponents of wind power have even suggested that it might be counter-productive, because we'd still need to have backup coal or nuclear plants (or some way of storing wind-generated electricity) for those times when there's not enough wind blowing. That would certainly be true if we made all our energy from one, single mega-sized wind turbine—but we don't! In reality, even countries that have large supplies of wind energy have plenty of other sources of power too (Denmark, for example, makes 20 percent of its electricity—and meets 43 percent of its peak load—with wind); as long as wind power is making less than half of a country's total energy, the variability of the wind is not a problem.

Photo: You can put lots of turbines together to make a wind farm, but you need to space them out to harvest the energy effectively. Combining the output from many wind farms in many different areas produces a smoother and more predictable power supply. This wind farm is at one of the world's windiest places: Altamont Pass, California, United States. Photo by courtesy of US Department of Energy.

Micro-wind turbines

If small is beautiful, micro-wind turbines—tiny power generators perched on a roof or mast—should be the most attractive form of renewable energy by far. Some manufacturers have pushed the technology aggressively, hinting to consumers about big savings on electricity bills and major benefits for the environment. The reality is a little different: micro-turbines do indeed bring economic and environmental benefits if they're sited in reliably windy areas, but they're less helpful in towns and cities where buildings make "energy harvesting" more of a challenge. So are micro-wind turbines really worth the investment? How do they compare with their big brothers?

Photo: Micro power to the people! This small, mast-mounted Rutland Windcharger is designed to trickle-charge 12V and 24V batteries, such as those used in small boats, far from the grid. At a wind speed of 40–55 km/h (20–30 knots), it will produce a handsome 140–240 watts of power. At 20 km/h (10 knots), it produces a rather more modest 27 watts.

How micro-wind turbines compare

These figures are simply designed to give a rough comparison of the differences between large-scale and micro-wind turbines. Bear in mind that there's a huge variety of micro-turbines.

• Mounting:
  • Conventional: Mounted on a tower roughly 80–100m (260–344ft) high.
  • Micro: Mounted on roof or on a small, freestanding mast typically ~10m (30ft) high.
• Rotor diameter:
  • Conventional: Up to 90m (300ft).
  • Micro: ~1–4m (40 inches to 12ft).
• Energy production:
  • Conventional: 1–2 megawatts (1000–2000 kilowatts).
  • Micro: 400–40,000 watts (0.4–40 kilowatts).
• Operates in wind speeds:
  • Conventional: ~10–55mph (16–90 km/h).
  • Micro: ~10–40 mph (16–64 km/h).
• Cost:
  • Conventional: ~$2 million.
  • Micro: $500–30,000 (typically under $10,000).
• Provides power to:
  • Conventional: 500–1500 homes.
  • Micro: 1 home.

How to set up your own micro-wind turbine

If you want to build your own micro-wind turbine, what do you need? Apart from the turbine itself, you also typically need a piece of electrical equipment called aninverter (which converts the direct-current electricity produced by the turbine's generator into alternating current you can use in your home) and appropriate electrical cabling. Your turbine will also need either a connection into the grid supply or batteries to store the energy it produces.

Aside from the equipment, here are a few pointers worth bearing in mind:

• The best place to start is with a professional assessment of your site's wind potential, which involves a series of measurements with an anemometer. Remember that wind turbines generally work far better in open, rural areas than mounted on rooftops in cities.
• Don't assume it will automatically be windy enough to make the investment in a microturbine worthwhile: a recent UK study of microturbines by Encraft found a mixed picture, with good performance from the best-located turbines and the very worst performing model (embarrassingly) not even producing enough electricity to power its own electronics—in other words, using more electricity overall than it produced. Some contribution to the environment!
• Depending on where you live, you will almost certainly need planning consent for a wind turbine, so check that out carefully with your local authority first.
• Sound out your neighbors before you start spending any money: instead of turning your "local friends" into bitter enemies with your rooftop propeller, maybe you could persuade them to join you in a community green-energy venture?
• Remember that roof-mounted wind turbines could prove noisy and cause problems with vibration.
• Don't forget that there are all kinds of other energy technologies that might give a quicker and better return on your investment and make more difference to the planet. Energy efficiency measures (such as improved heat insulation) generally give the quickest payback for least cost and make the most difference in the short-term, and solar hot water systems work very well almost anywhere. Ground-source heat pumps are also worth a look.

Photo: Although micro-wind turbines on homes have proved controversial, they definitely have their place. Here's the Rutland Windhcharger from our top photo helping to charge the batteries in a go-anywhere, portable highway construction sign. It's getting help from the large flat solar panel mounted on top. This is a great example of how micro-wind turbines can be useful if you put them in the right place, at the right time.

Electricity

If you've ever sat watching a thunderstorm, with mighty lightning bolts darting down from the sky, you'll have some idea of the power of electricity. A bolt of lightning is a sudden, massive surge of electricity between the sky and the ground beneath. The energy in a single lightning bolt is enough to light 100 powerful lamps for a whole day or to make a couple of hundred thousand slices of toast!

Electricity is the most versatile energy source that we have; it is also one of the newest: homes and businesses have been using it for not much more than a hundred years. Electricity has played a vital part of our past. But it could play a different role in our future, with many more buildings generating their own renewable electric power using solar cells and wind turbines. Let's take a closer look at electricity and find out how it works!

What is electricity?

Electricity is a type of energy that can build up in one place or flow from one place to another. When electricity gathers in one place it is known as static electricity (the word static means something that does not move); electricity that moves from one place to another is called current electricity.

Static electricity

Static electricity often happens when you rub things together. If you rub a balloon against your jumper 20 or 30 times, you'll find the balloon sticks to you. This happens because rubbing the balloon gives it an electric charge (a small amount of electricity). The charge makes it stick to your jumper like a magnet

, because your jumper gains an opposite electric charge. So your jumper and the balloon attract one another like the opposite ends of two magnets.

Have you ever walked across a nylon rug or carpet and felt a slight tingling sensation? Then touched something metal, like a door knob or a faucet (tap), and felt a sharp pain in your hand? That is an example of an electric shock. When you walk across the rug, your feet are rubbing against it. Your body gradually builds up an electric charge, which is the tingling you can sense. When you touch metal, the charge runs instantly to Earth—and that's the shock you feel.

Lightning is also caused by static electricity. As rain clouds move through the sky, they rub against the air around them. This makes them build up a huge electric charge. Eventually, when the charge is big enough, it leaps to Earth as a bolt of lightning. You can often feel the tingling in the air when a storm is brewing nearby. This is the electricity in the air around you. Read more about this in our article on capacitors.

Photo: Lightning in South Lakewood, Colorado. Photo by Dave Parsons courtesy of US DOE/NREL (Department of Energy/National Renewable Energy Laboratory).

How static electricity works

Electricity is caused by electrons, the tiny particles that "orbit" around the edges of atoms, from which everything is made. Each electron has a small negative charge. An atom normally has an equal number of electrons and protons (positively charged particles in its nucleus or center), so atoms have no overall electrical charge. A piece of rubber is made from large collections of atoms called molecules. Since the atoms have no electrical charge, the molecules have no charge either—and nor does the rubber.

Suppose you rub a balloon on your jumper over and over again. As you move the balloon back and forward, you give it energy. The energy from your hand makes the balloon move. As it rubs against the wool in your jumper, some of the electrons in the rubber molecules are knocked free and gather on your body. This leaves the balloon with slightly too few electrons. Since electrons are negatively charged, having too few electrons makes the balloon slightly positively charged. Your jumper meanwhile gains these extra electrons and becomes negatively charged. Your jumper is negatively charged, and the balloon is positively charged. Opposite charges attract, so your jumper sticks to the balloon.

That's a very brief introduction to static electricity. You'll find much more about it (and why it's caused by something called triboelectricity) in our main article onstatic electricity.

Photo: A classic demonstration of static electricity you may have seen in your school. When this girl touches the metal ball of a Van de Graaff static electricity generator, she receives a huge static electric charge and her hair literally stands on end! Each strand of hair gets the same static charge and like charges repel, so her hairs push away from one another. Photo courtesy of Sandia National Laboratories/US Department of Energy.

Current electricity

When electrons move, they carry electrical energy from one place to another. This is called current electricity or an electric current. A lightning bolt is one example of an electric current, although it does not last very long. Electric currents are also involved in powering all the electrical appliances that you use, from washing machines to flashlights and from telephones to MP3 players. These electric currents last much longer.

Have you heard of the terms potential energy and kinetic energy? Potential energy means energy that is stored somehow for use in the future. A car at the top of a hill has potential energy, because it has the potential (or ability) to roll down the hill in future. When it's rolling down the hill, its potential energy is gradually converted into kinetic energy (the energy something has because it's moving). You can read more about this in our article on energy.

Static electricity and current electricity are like potential energy and kinetic energy. When electricity gathers in one place, it has the potential to do something in the future. Electricity stored in a battery is an example of electrical potential energy. You can use the energy in the battery to power a flashlight, for example. When you switch on a flashlight, the battery inside begins to supply electrical energy to the lamp, making it give off light. All the time the light is switched on, energy is flowing from the battery to the lamp. Over time, the energy stored in the battery is gradually turned into light (and heat) in the lamp. This is why the battery runs flat.

Picture: A battery like this stores electrical potential energy in a chemical form. When the battery is flat, it means you've used up all the stored energy inside by converting it into other forms.

Electric circuits

For an electric current to happen, there must be a circuit. A circuit is a closed path or loop around which an electric current flows. A circuit is usually made by linking electrical components together with pieces of wire cable. Thus, in a flashlight, there is a simple circuit with a switch, a lamp, and a battery linked together by a few short pieces of copper wire. When you turn the switch on, electricity flows around the circuit. If there is a break anywhere in the circuit, electricity cannot flow. If one of the wires is broken, for example, the lamp will not light. Similarly, if the switch is turned off, no electricity can flow. This is why a switch is sometimes called a circuit breaker.

You don't always need wires to make a circuit, however. There is a circuit formed between a storm cloud and the Earth by the air in between. Normally air does not conduct electricity. However, if there is a big enough electrical charge in the cloud, it can create charged particles in the air called ions (atoms that have lost or gained some electrons). The ions work like an invisible cable linking the cloud above and the air below. Lightning flows through the air between the ions.

How electricity moves in a circuit

Materials such as copper metal that conduct electricity (allow it to flow freely) are called conductors. Materials that don't allow electricity to pass through them so readily, such as rubber and plastic, are called insulators. What makes copper a conductor and rubber an insulator?

A current of electricity is a steady flow of electrons. When electrons move from one place to another, round a circuit, they carry electrical energy from place to place like marching ants carrying leaves. Instead of carrying leaves, electrons carry a tiny amount of electric charge.

Electricity can travel through something when its structure allows electrons to move through it easily. Metals like copper have "free" electrons that are not bound tightly to their parent atoms. These electrons flow freely throughout the structure of copper and this is what enables an electric current to flow. In rubber, the electrons are more tightly bound. There are no "free" electrons and, as a result, electricity does not really flow through rubber at all. Conductors that let electricity flow freely are said to have a high conductance and a low resistance; insulators that do not allow electricity to flow are the opposite: they have a low conductance and a high resistance.

For electricity to flow, there has to be something to push the electrons along. This is called an electromotive force (EMF). A battery or power outlet creates the electromotive force that makes a current of electrons flow. An electromotive force is better known as a voltage.

Direct current and alternating current

Electricity can move around a circuit in two different ways. In the big picture up above, you can see electrons racing around a loop like race cars on a track, always going in the same direction. This type of electricity is called direct current (DC) and most toys and small gadgets have circuits that work this way.

The bigger appliances in your home use a different kind of electricity called alternating current (AC). Instead of always flowing the same way, the electrons constantly reverse direction—about 50–60 times every second. Although you might think that makes it impossible for energy to be carried round a circuit, it doesn't! Take the flashlight bulb in the circuit above. With direct current, new electrons keep streaming through the filament (a thin piece of wire inside the bulb), making it heat up and give off light. With alternating current, the same old electrons whiz back and forth in the filament. You can think of them running on the spot, heating up the filament so it still makes bright light we can see. So both types of current can make the lamp work even though they flow in different ways. Most other electric appliances can also work using either direct or alternating current, though some circuits do need AC to be changed to DC (or vice versa) to work correctly.

Artwork: Top: In a direct current (DC) circuit, electrons always flow in the same direction. Bottom: In an alternating current (AC) circuit, the electrons reverse direction many times each second.

Electromagnetism

Electricity and magnetism are closely related. You might have seen giant steel electromagnets working in a scrapyard. An electromagnet is a magnet that can be switched on and off with electricity. When the current flows, it works like a magnet; when the current stops, it goes back to being an ordinary, unmagnetized piece of steel. Scrapyard cranes pick up bits of metal junk by switching the magnet on. To release the junk, they switch the magnet off again.

Electromagnets show that electricity can make magnetism, but how do they work? When electricity flows through a wire, it creates an invisible pattern of magnetism all around it. If you put a compass needle near an electric cable, and switch the electricity on or off, you can see the needle move because of the magnetism the cable generates. The magnetism is caused by the changing electricity when you switch the current on or off.

This is how an electric motor works. An electric motor is a machine that turns electricity into mechanical energy. In other words, electric power makes the motor spin around—and the motor can drive machinery. In a clothes washing machine, an electric motor spins the drum; in an electric drill, an electric motor makes the drill bit spin at high speed and bite into the material you're drilling. An electric motor is a cylinder packed with magnets around its edge. In the middle, there's a core made of iron wire wrapped around many times. When electricity flows into the iron core, it creates magnetism. The magnetism created in the core pushes against the magnetism in the outer cylinder and makes the core of the motor spin around. Read more in our main article on electric motors.

Make an electromagnet

You can make a small electromagnet using a battery, some insulated (plastic-covered) copper wire, and a nail. Here are a couple of websites that tell you what to do step-by-step:

• How do I make an electromagnet?: Handy hints from Jefferson Lab.
• Science Projects: Make an electromagnet: from the California Energy Commission.

Picture: Why not make an electromagnet? All you need is a few common household items.

Making electricity

Just as electricity can make magnetism, so magnetism can make electricity. A dynamo is a bit like an electric motor inside. When you pedal your bicycle, the dynamo clipped to the wheel spins around. Inside the dynamo, there is a heavy core made from iron wire wrapped tightly around—much like the inside of a motor. The core spins freely inside some large fixed magnets. As you pedal, the core rotates inside these outer magnets and generates electricity. The electricity flows out from the dynamo and powers your bicycle lamp.

The electric generators used in power plants work in exactly the same way, only on a much bigger scale. Instead of being powered by someone's legs, pedaling furiously, these large generators are driven by steam. The steam is made by burning fuels or by nuclear reactions. Power plants can make enormous amounts of electricity, but they waste quite a lot of the energy they produce. The energy has to flow from the plant, where it is made, to the homes, offices, and factories where it is used down many miles of electric power cable. Delivering electricity this way can waste up to two thirds of the power originally produced!

Another problem with power plants is that they make electricity by burning "fossil fuels" such as coal, gas, or oil. This creates pollution and adds to the problem known as global warming (the way Earth is steadily heating up because of the energy people are using). Another problem with fossil fuels is that supplies are limited and they are steadily running out.

Photo: Making clean, renewable energy from the wind. Each of these turbines contains an electricity generator in the top section, just behind the spinning rotors.

There are other ways to make energy that are more efficient, less polluting, and do not contribute to global warming. These types of energy are called renewable, because they can last indefinitely. Examples of renewable energy include wind turbines and solar power. Unlike huge electric power plants, they are often much more efficient ways of making electricity. Because they can be sited closer to where the electricity is used, less energy is wasted transmitting power down the wires.

Wind turbines are effectively just electric generators with a propeller on the front. The wind turns the propeller, which spins the generator inside, and makes a study current of electricity.

Unlike virtually every other way of making electricity, solar cells (like the ones on calculators and digital watches) do not work using electricity generators and magnetism. When light falls on a solar cell, the material it is made from (silicon) captures the light's energy and turns it directly into electricity. Potentially, this means solar cells are an extremely efficient way to make electricity. A home with solar electric panels on the roof might be able to make most of its own electricity, for example.

Electricity and electronics

Electricity is about using relatively large currents of electrical energy to do useful jobs, like driving a washing machine or powering an electric drill.Electronics is a very different kind of electricity. It's a way of controlling things using incredibly tiny currents of electricity—sometimes even individual electrons! Suppose you have an electronic clothes washing machine. Large currents of electricity come from the power outlet (mains supply) to make the drum rotate and heat the water. Smaller currents of electricity operate the electronic components in the washing machine's programmer unit. These tiny currents control the bigger currents, making the drum rotate back and forth, starting and stopping the water supply, and so on. Read more in our main article on electronics.

Photo: A transistor (a typical electronic component) on a circuit board. Components like this run on electricity, just like clothes washing machines, but they use much smaller currents and voltages.

The power of electricity

Before the invention of electricity, people had to make energy wherever and whenever they needed it. Thus, they had to make wood or coal fires to heat their homes or cook food. The invention of electricity changed all that. It meant energy could be made in one place then supplied over long distances to wherever it was needed. People no longer had to worry about making energy for heating or cooking: all they had to do was plug in and switch on—and the energy was there as soon as they wanted it.

Another good thing about electricity is that it's like a common "language" that all modern appliances can "speak." You can run a car using the energy in gasoline, or you can cook food on a barbecue in your garden using charcoal, though you can't run your car on charcoal or cook food with gasoline. But electricity is quite different. You can cook with it, run cars on it, heat your home with it, and charge your cellphone with it. This is the great beauty and the power of electricity: it's energy for everyone, everywhere, and always.

Measuring electricity

We can measure electricity in a number of different ways, but a few measurements are particularly important.

Photo: You can use a digital multimeter like this to measure voltage, current, and resistance.

Voltage

The voltage is a kind of electrical force that makes electricity move through a wire and we measure it in volts. The bigger the voltage, the more current will tend to flow. So a 12-volt car battery will generally produce more current than a 1.5-volt flashlight battery.

Current

Voltage does not, itself, go anywhere: it's quite wrong to talk about voltage "flowing through" things. What moves through the wire in a circuit is electrical current: a steady flow of electrons, measured in amperes (or amps).

Power

Together, voltage and current give you electrical power. The bigger the voltage and the bigger the current, the more electrical power you have. We measure electric power in units called watts. Something that uses 1 watt uses 1 joule of energy each second.

The electric power in a circuit is equal to the voltage × the current (in other words: watts = volts × amps). So if you have a 100-watt (100 W) light and you know your electricity supply is rated as 120 volts (typical household voltage in the United States), the current flowing must be 100/120 = 0.8 amps. If you're in Europe, your household voltage is more likely 230 volts. So if you use the same 100-watt light, the current flowing is 100/230 = 0.4 amps. The light burns just as brightly in both countries and uses the same amount of power in each case; in Europe it uses a higher voltage and lower current; in the States, there's a lower voltage and higher current. (One quick note: 120 volts and 230 volts are the "nominal" or standard household voltages—the voltages you're supposed to have, in theory. In practice, your home might have more or less voltage than this, for all sorts of reasons, but mainly because of how far you are from your local power plant or power supply.)

Energy

Power is a measurement of how much energy you're using each second. To find out the total amount of energy an electric appliance uses, you have to multiply the power it uses per second by the total number of seconds you use it for. The result you get is measured in units of power × time, often converted into a standard unit called the kilowatt hour (kWh). If you used an electric toaster rated at 1000 watts (1 kilowatt) for a whole hour, you'd use 1 kilowatt hour of energy; you'd use the same amount of energy burning a 2000 watt toaster for 0.5 hours or a 100-watt lamp for 10 hours. See how it works?

Electricity meters (like the one shown in the photo above, from my house) show the total number of kilowatt hours of electricity you've used. 1 kilowatt hour is equal to 3.6 million joules (J) of energy (or 3.6 megajoules if you prefer).

You can measure your energy consumption automatically with an energy monitor.

A brief history of electricity

Picture: Nikola Tesla (1856–1943) pioneered the alternating current power system most of us use today. Even so, his rival, Thomas Edison (1846–1931), is still popularly remembered as the inventor who gave the world electric power. Photograph by Sarony; engraving by T. Johnson, c.1906, courtesy of US Library of Congress.

• 600 BCE: Greek philosopher Thales of Miletus (c.624–546 BCE) discovered static electricity.
• 1600 CE: English scientist William Gilbert (1544–1603) was the first person to use the word "electricity." He believed electricity was caused by a moving fluid called humor.
• 1733: French scientist Charles du Fay (1698–1739) found that there were two different kinds of static electric charge.
• 1752: American printer, journalist, scientist, and statesman Benjamin Franklin (1706–1790) carried out further experiments and named the two kinds of electric charge "positive" and "negative."
• 1780: Italian biologist Luigi Galvani (1737–1798) touched two pieces of metal to a dead frog's leg and made it jump. This led him to believe electricity is made inside animals' bodies.
• 1785: French scientist Charles Augustin de Coulomb (1736–1806) explored the mysteries of electric fields: the electrically active areas around electric charges.
• 1800: One of Galvani's friends, an Italian physics professor named Alessandro Volta (1745–1827), realized "animal electricity" was made by the metals Galvani had used. After further research, he found out how to make electricity by joining different metals together and invented batteries.
• 1827: German physicist Georg Ohm (1789–1854) found some materials carry electricity better than others and developed the idea of resistance.
• 1820: Danish physicist Hans Christian Oersted (1777–1851) put a compass near an electric cable and discovered that electricity can make magnetism.
• 1821: A French physicist called Andre-Marie Ampère (1775–1836) put two electric cables near to one another, wired them up to a power source, and watched them push one another apart. This showed electricity and magnetism can work together to make a force.
• 1821: Michael Faraday (1791–1867), an English chemist and physicist, developed the first, primitive electric motor.
• 1830s: American physicist Joseph Henry (1797–1879) and British inventor William Sturgeon (1783–1850) independently made the first practical electromagnets and electric motors.
• 1831: Building on his earlier discoveries, Michael Faraday invented the electric generator.
• 1840: Scottish physicist James Prescott Joule (1818–1889) proved that electricity is a kind of energy.
• 1870s: Belgian engineer Zénobe Gramme (1826–1901) made the first large-scale electric generators.
• 1873: James Clerk Maxwell (1831–1879), another British physicist, set out a detailed theory of electromagnetism (how electricity and magnetism work together).
• 1881: The world's first experimental electric power plant opened in Godalming, England.
• 1882: Thomas Edison (1846–1931) built the first large-scale electric power plants in the USA.
• 1890s: Edison's former employee Nikola Tesla (1856–1943) promoted alternating current (AC) electricity, a rival to the direct current (DC) system promoted by Edison. Edison and Tesla battled for supremacy and, although Edison is remembered as the pioneer of electric power, it was Tesla's AC system that ultimately triumphed.

Stepper motors

R

each out and touch the tip of your finger to the tip of your nose. No problem! Try it again with your eyes closed and it's still simple: you never miss. Even in clumsy people like me, the brain mostly has control of the body. In athletes, artists, ballet dancers, and surgeons, "control" means absolute precision. Now imagine trying to build a robot with the same degree of mechanical excellence, using gears, wheels, and levers to accomplish what the body does with muscle and bone. It's a much taller order, which makes the human body seem even more impressive. One of the big difficulties of making well-behaved robots is that simple electric motors are impossible to move precisely. That's why a lot of robots swap ordinary motors for what are called stepper motors (or, sometimes, stepping motors), which can turn through "steps"—well-defined angles—under precise electronic control. What are they are how do they work? Let's take a closer look!

Photo: A typical DC stepper motor. Note that there are multiple leads coming out of it (unlike with a simple DC motor, which has only two leads). Photo courtesy of MakerBot Industries published on Flickr under a Creative Commons Licence.

What's wrong with ordinary electric motors?

An ordinary electric motor is based on a simple bit of magnet science we all learn at school: unlike poles attract, like poles repel. Here's how a basic motor works. You take a ring-shaped magnet, put a coil of wire inside it, and feed electricity through the wire. The wire becomes a temporary magnet powered by electricity—an electromagnet, in other words—and the magnetic field it creates repels the field from the permanent magnet that surrounds it. By switching the current on and off with a clever little device called a commutator, and some electrical contacts called brushes, you can make the wire rotate in the same direction indefinitely. Feed electricity (electrical energy) into it and you get motion (mechanical energy) back out. That's the essence of an ordinary motor that uses DC (direct current) electricity. If you're less than sure how a motor like this works, you might want to check out our introductory article about electric motors.

Photo: The powerful electric motor from an old lawn mower. The slots at the front are part of the commutator, which is an ingenious device that reverses the electric current and keeps the rotor (the rotating, central part of the motor) spinning in the same direction.

We can also make motors that work using AC (alternating current) instead of DC. Although they're engineered in a radically different way, they're still based on "like poles repel, unlike poles attract": the electricity that powers the motor creates magnetic attraction and repulsion, and a force that makes the motor spin. You'll find more about AC motors—which are also called induction motors—in our article on AC induction motors.

Whether they're powered by DC or AC, ordinary motors are the hidden electric muscles that power modern life: you'll find them in all kinds of gadgets and gizmos in the world around you, from food blenders and refrigerators to vacuum cleaners and electric trains. But in all these machines, the rotors of their motors spin continuously. When you vacuum a carpet or commute to work by subway, the motors that are working for you turn around an arbitrary number of times: there's no precise control over how many times they rotate and what angle they spin through—and it really doesn't matter.

Now suppose you want to make an electric-powered robot arm that turns through an exact angle (an exact number of degrees) so it can successfully grab a cup ofcoffee off your desk. You could fit an electric motor onto a wooden or plastic lever to make it turn when you switch on the power, and you could flick the power on very briefly so the arm sweeps through a certain angle and then stops. The trouble is, there's no way of knowing how much of an angle the motor (or the arm) will move: it depends on everything from the power of the motor and the electric current driving it to the weight of the arm and even which way the wind is blowing. A motor that moves in such an arbitrary way is no use whatever in robotics: your coffee will surely end up on the floor! That's where a stepper motor comes in: it's a special kind of DC motor designed so you can make it rotate through a precise angle, instead of spinning round by a random amount.

Photo: Motor mouth: This "emotional" robot has a face that can show different expressions. The various parts are operated by stepper motors, precisely controlled by electronic circuits.

What exactly is a stepper motor?

Stepper motors are different from ordinary DC motors in at least four important ways.

The first difference you notice is that they have no brushes or commutator (the parts of a DC motor that reverse the electrical current and keep the rotor—the rotating part of a motor—constantly turning in the same direction). In other words, stepper motors are examples of what we call brushless motors. (You'll also find brushless motors in many electric vehicles, hidden away in the wheel hubs; used in that way, they're called hub motors.)

The second major difference is in what rotates. Remember that in a basic DC motor, there is an outer permanent magnet or magnets that stays static, known as the stator, and an inner coil or coils of wire that rotates inside it, which is the rotor. In a brushless hub-motor, the coils of wire are static in the center and the permanent magnets spin around them on the outside. A stepper motor is different again. This time, the permanent magnets are on the inside and rotate (making up the rotor), while the coils are on the outside and stay static (making up the stator).

The third big difference between an ordinary DC motor and a stepper motor is in the design of the stator and the rotor. Instead of one large magnet on the outside (the stator) and one large coil rotating inside it (the rotor), a stepper motor has an inner magnet effectively divided up into many separate sections, which look like teeth on a gear wheel. The outer coils have corresponding teeth that provide magnetic impulses, attracting, repelling, and making the teeth of the inner wheel rotate by small steps. This will become clear in a moment when we look at some pictures.

The final difference is that a stepper motor can stay still, in a certain position, once it's rotated through a particular angle. That's obviously crucially important if you want a motor to power something like a robot arm, which might have to rotate a certain amount and then remain in precisely that spot while another part of the robot does something else. This feature is sometimes called holding torque(torque is the rotary force something has, so "holding torque" simply means a stepping motor's ability to stay still).

Photo: The philosophy of steps: we think of steps as a way to climb up, but they're also a way to break a fixed distance into equal-sized pieces so we get more control over our movements. We can think of them as turning vague, variable, analogamounts of distance into specific, discrete, digital chunks.

How does a stepper motor work?

The basic construction

I'm going to simplify stepper motors here to illustrate the simple, central idea: the (inside) rotor of a stepper motor turns by small, discrete amounts (steps) because the (outside) stator applies magnetic impulses that pull and push it around.

The rotor

The rotor itself is made from two discs, a little like gears, one of which is a magnetic north pole (red) and the other is a south pole (blue). When we put the two discs back to back, we get north and south pole teeth alternating around the edge. If you find that hard to picture, imagine your left hand is a magnetic north pole and is colored red, while your right hand is a magnetic south pole and colored blue. If you put one hand on top of the other so the fingers of one hand alternate with the fingers of the other, then look down, you'll see alternating north and south pole "teeth" (the fingers) around the edge. That's effectively what we have in the rotor of a stepper motor.

Photo: A stepper motor's rotor is made from two discs placed together so we get a series of alternating north and south poles. I've simulated the idea by coloring my hands and putting them on top of one another so the fingers alternate when viewed from above.

The stator

Around the edge of the rotor, we have the stator: in this example, four electromagnets that can be switched on and off individually. Generally the electromagnets in a stepper motor work in pairs, with each opposing pair of magnets switching on together to make a north pole at the same time, followed by the magnets at right angles, which also work together. I prefer to draw it a slightly different way, which I think is simpler and easier to understand. Exactly what switches on when depends on how many rotor teeth (steps) there are and how many electromagnet coils surround them: the geometry and alignment of a stepper motor has to be just right to make the rotor turn.

How it rotates

1. The right electromagnet is energized and becomes a north pole (red) and the left electromagnet becomes a south pole (blue). This pulls the rotor around by one step so a blue tooth on the rotor snaps toward the right electromagnet and a red tooth snaps toward the left electromagnet.
2. Now the bottom electromagnet becomes a north pole, the top magnet becomes a south pole, and the two horizontal magnets are switched off. Again, the teeth of the rotor are pulled around by one step.
3. The vertical magnets are now switched off and the horizontal magnets are switched on again, but with the opposite polarity (pattern of magnetism) that they had before. The teeth of the rotor advance by one more step.
4. Finally, the vertical magnets are switched on again, in the opposite polarity to before, and the horizontal magnets are switched off. The rotor mores around one more step. The whole cycle then repeats.

Remember that a stepper motor isn't really designed to keep spinning around and around: by sending as many or as few impulses to the outer electromagnets as necessary, we can make the rotor turn through a certain number of steps (and, therefore, by a precise angle). We can make it rotate the opposite way by reversing the electric current.

Types of stepper motors

This is just a simple overview of stepper motors and I won't go into details about all the numerous different varieties you'll find. A couple of technical terms that are worth knowing crop up often in the literature (and in web pages) about stepper motors, often without any explanation.

Poles

The motor I've illustrated here has a rotor magnet divided into lots of alternating north and south poles, so this design is known as a multi-pole motor. The more poles, the shorter the distance the motor rotates on each step and the more precisely it can be controlled.

Phases

In a motor, a "phase" usually means one or two opposing electromagnets that operate alternately (out of sync with one another or out of phase, if you prefer). The motor I've illustrated up above has two phases (two pairs of electromagnets, so four electromagnets in total, arranged at 90 degrees). In a three-phase stepper motor, you might have three electromagnets arranged at an angle of 120 degrees (so three individual electromagnets, although a three-phase motor could also have three pairs arranged 60 degrees apart). A four-phase motor has eight electromagnets arranged in four pairs, with each one separated from the next by 45 degrees.

Advantages and disadvantages of stepper motors

The reason for using a stepper motor is to achieve precise control: you can make it move through a defined angle. But there are drawbacks too. Stepper motors can sometimes be quite jerky, because they start and stop each step with a sudden impulse, which isn't always what you want if you're trying to build a precision machine. An alternative to using a stepper motor is to use a servo motor: a motor with a built-in feedback mechanism. Typically, a servo motor has what's called an optical encoder attached to its rotor. In plain English, that's a black-and-white patterned disc that moves in front of something like a photoelectric cell. As the disc turns, the cell detects the black and white pattern and an electronic circuit figures out from this exactly how much the disc has rotated. Using this feedback, the motor can be controlled more smoothly (and typically much more precisely) than a simple stepper motor. Servo motors are much more sophisticated in design than stepper motors and tend to be more expensive, which is why steppers are often used instead.

Photo: Inside an inkjet printer, a very common application of stepper motors. You can see two stepper motors here: the top one moves the ink cartridge and print head from left to right by turning the black and brown belt, while the bottom one spins the white gears, which turn the paper rollers and make the paper feed through.

Electronics

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. Theelectronics 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 from a webcam.

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 lamps. Generally, electrical appliances need a great deal of energy to make them work so they use quite large (and often quite dangerous) electric currents.

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.

Photo: The 2500-watt heating element inside this 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.

Analog and digital electronics

Photo: Digital technology: Large digital clocks like this are quick and easy for runners to read. Photo by Jhi L. Scott courtesy of US Navy.

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.

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 vibrate 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 digital electronics.

Electronic components

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 individual parts.

The circuits inside pieces of electronic equipment are a bit like cities too: they're packed with components (similar to buildings) that do different jobs and the components are linked together by cables or printed metal connections (similar to 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:

Resistors

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.

Diodes

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).

Capacitors

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.

Transistors

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.)

Read more in our main article about transistors.

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

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 separate pathways. Generally speaking, the more complex the circuit, the more intricate the operations it can perform.

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 called "breadboard".

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!

Electronics around us

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-raymachines. 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 ways?

A brief history of electronics

• 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 it.
• 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 previous decade.
• 1897: British physicist J.J. Thomson (1856–1940) shows that cathode rays are negatively charged particles. 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.
• 1987: American scientists Theodore Fulton and Gerald Dolan of Bell Laboratories develop the first single-electron transistor.