Electrons traveling through circuits can play your favorite songs, turn your television on and off, or capture digital photos of your friends. When gadgets use electrons in this way, we say they are electronic - they use electricity in a way that's more precise and finely controlled than the kind that powers simple home appliances. Electronics is the secret power behind calculators, computers, robots, and the Internet.
It takes quite a lot of electricity (large electrical currents) to boil water or heat a home. Electronics uses carefully controlled electric currents thousands or millions of times smaller, and sometimes just individual electrons, to do useful things.
Electronics uses complex circuits, but these circuits only need tiny currents. Because they don't consume much energy, many electronic appliances can be battery-powered.
We can use electronics to switch things on and off. When you press a button on a TV remote control, an electronic circuit detects what you want and sends an invisible beam to the TV set. The TV detects this and another circuit responds.
Electronic circuits can boost tiny electric currents into bigger ones. An electric guitar uses electromagnets to convert the movement of the strings into electric currents. These are boosted in an electronic amplifier, which powers a loudspeaker.
The electronic circuits in computers digest information. When you type, electronic circuits decode the keys you press, understand what you are typing, and work out where to display the letters.
In cell phones, electronic circuits convert our speech or text into a form that can be beamed through the air using invisible radio waves. They can also convert radio waves from other phones back into spoken words or text messages.
An electronic circuit is made of building blocks called components. A transistor radio might have a few dozen components, while the processor and memory chips in a computer could have billions. Four components are particularly important and appear in almost every single circuit: resistors, capacitors, diodes, and transistors.
Resistors reduce an electric current so it's less powerful. Some have a fixed size, while others vary. The volume on a TV set is a variable resistor. As you move it, its resistance rises or falls, altering the current, and making the sound quieter or louder.
Capacitors store electricity in a sandwich of metal foil separated by air or plastic. It takes a precise time for them to charge up, so they are often used in circuits that work as timers. Capacitors are also used to detect key punches on cell phone and tablet touchscreens.
A diode is the electronic version of a one-way street: a current can only flow along it in one direction. Diodes are often used to convert electricity that flows in both directions (alternating current) into electricity that flows only one way (direct current).
Transistors can switch electric currents on and off or convert small currents into bigger ones. Most transistors are used in computers. A powerful computer chip contains a billion or more transistors.
Electronic components such as transistors are about as big as a pea, so a computer with a billion of them would be enormous. It would also be difficult to make, unreliable, and power hungry. In 1958, two US engineers named Jack Kilby and Robert Noyce found ways of shrinking electronic components and their connections into a tiny space. This idea became known as an integrated circuit, or chip.
Printed circuit boards
Electronic circuits are often made in the millions for cell phones or TVs. To save money and reduce mistakes, machines wire components into readymade printed circuit boards (PCBs). Each is unique to a particular device. The circuit is made from metal connections (tracks) that crisscross the board, linking the components. There are no moving parts, so PCBs are very reliable.
Inside a circuit board: A circuit board is made from interconnected chips. Each chip has an integrated circuit inside it, containing millions or billions of components.
Chips are intricate and have to be made in ultraclean, dust-free conditions. Many chips are made at once on the surface of a thin wafer sliced from a crystal of silicon (a chemical element found in sand).
Engineers are constantly finding new ways to add more components into chips. The power of computers (number of transistors on a chip) has doubled roughly every two years since the first single-chip computer appeared in 1971. This is called Moore's law, named after Gordon Moore (1929-), a founder of the Intel chip company.
Most of the gadgets we rely on every day use digital technology: they convert information into numbers (digits) and process the numbers instead of the original information. Digital cameras turn pictures of the world into patterns of numbers (digital photos), and cell phones send and receive calls not as sounds but as long strings of numbers. Gadgets like these use integrated circuits to convert, store, and process information in digital form - a technology known as digital electronics.
Analog and digital
Ordinary information, like the sound waves made by a guitar, is called analog information. If you use an oscilloscope (an electronic graph-drawing machine) to draw these sound waves, they look exactly like the sounds you can hear - the waves rise and fall as the sound rises and falls. Digital technology converts this analog information into numbers through a process called sampling.
To convert music into a digital MP3 file, sound waves have to be turned into numbers. The size of the waves is sampled (measured) at different times and its value recorded, making a string of numbers. The more often the wave is sampled, the better the result.
Computers process digital information with circuits called logic gates. These compare two numbers (0 or 1) and produce a third based on the result. The main types are AND, OR, and NOT.
This compares the two numbers and switches on if both the numbers are the same.
This switches on if either of the two numbers is a 1. If both numbers are 0, it switches off.
This reverses (inverts) whatever goes into it. A 0 becomes a 1, and vice versa.
Calculators: Calculators use logic gate circuits to add and subtract numbers. Dividing is done by subtracting repeatedly; multiplying is done by adding a number over and over again.
Memory: Computers store information as well as process it. This happens in memories made from transistors. To store a word, a computer converts it into a pattern of zeros and ones called binary code. Each zero or one is stored by its own transistor, switched on or off.