Electronic devices are used as tools in many areas of advanced research. Shown here is a Scanning Electron Microscope which uses electrons to produce a highly magnified image on a computer screen.

A diode is an electronic component through which current passes in only one direction. Light-emitting diodes (LEDs) are semiconductors that produce light when current passes through them. They are used in many common devices, such as the tuning indicator on a radio. An arrangement of seven LEDs in the shape of an ‘8’ can be used to display any number from 0 to 9. This arrangement is often used on calculators and digital watches.

A vacuum tube amplifier circuit consists of a triode, load resister, batteries, and variable voltage source. The triode is an evacuated glass tube that consists of a cathode C, anode A, and grid G. Battery A heats the filament in the cathode so that electrons are free to move. Battery B maintains a potential difference between the cathode and anode and supplies the energy that the electrons gain when they flow from the cathode to the anode. This flow can be controlled by applying a negative voltage to the grid with Battery C. The higher the negative voltage on the grid, the fewer electrons flow from the cathode to the anode. Small changes in grid voltage from a radio or audio signal S can produce large variations in current flow from cathode to anode and throughout the rest of the circuit.

A close-up photograph of a smoke detector’s circuit board reveals its inner components, which include transistors, resistors, capacitors, diodes, and inductors. The rounded silver containers house the transistors that make the circuit work. Transistors are capable of serving many functions, such as amplifier, switch, and oscillator. Each transistor consists of a small piece of silicon that has been “doped,” or treated with impurity atoms, to create n-type and p-type semiconductors. Invented in 1940, transistors are a fundamental component in nearly all modern electronic devices.

An integrated circuit (IC) consists of many circuit elements such as transistors and resistors fabricated on a single piece of silicon or other semiconducting material. The tiny microprocessor shown here is the heart of the personal computer (PC). Such devices may contain several million transistors and be able to execute over 100 million instructions per second. The rows of leglike metal pins are used to connect the microprocessor to a circuit board.

This integrated circuit, an F-100 microprocessor, is only 0.6 cm square and is small enough to pass through the eye of a needle.

Integrated circuits (ICs) make the microcomputer possible; without them, individual circuits and their components would take up far too much space for a compact computer design. Also called a chip, the typical IC consists of elements such as resistors, capacitors, and transistors packed on a single piece of silicon. In smaller, more densely-packed ICs, circuit elements may be only a few atoms in size, which makes it possible to create sophisticated computers the size of notebooks. A typical computer circuit board features many integrated circuits connected together.

This illustration shows a simplified schematic diagram of an oscillator circuit. The tuned circuit contains an inductor coil L₁, a smaller inductor coil L₂, and a capacitor C.

Computers use digital logic to perform operations. Digital logic involves making successive “true” or “false” decisions, which may also be represented by 1 and 0, respectively. Logic circuits, which are at the heart of computer chips, are designed to make a series of these decisions via junctures called gates. Gates are designed and arranged to make different kinds of “decisions” about the input they receive. Individual input and output values are always either true or false and are relayed through the circuit in the form of different voltages. This circuit uses 4 NOR gates, each of which makes the decision “neither A nor B.” The NOR operation yields an output of 0 whenever one or more of the input values is 1. The table shows input values (A, B) and output value (F) for the NOR gate. A circuit map (bottom) shows the layout of a NOR gate and its components, indicating voltage values when the inputs are 0,0 and the output is 1.

Digital circuits operate in the binary number system, which means that all circuit variables must be either 1 or 0. The algebra used to solve problems and process information in digital systems is called Boolean algebra; it deals with logic, rather than calculating actual numeric values. Boolean algebra is based on the idea that logical propositions are either true or false, depending on the type of operation they describe and whether the variables are true or false. “True” corresponds to the digital value of 1, while “false” corresponds to 0. These diagrams show various electronic switches, called gates, each of which performs a specific Boolean operation. There are three basic Boolean operations, which may be used alone or in combination: logical multiplication (AND gate), logical addition (OR gate), and logical inversion (NOT gate). The accompanying tables, called truth tables, map all of the potential input combinations against yielded outputs.