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188 Science and Technology

FIND OUT MORE. Circuits 184–185 • Elements 160–161 • Sound 176–177 • Telecommunications 192–193

Electronic circuits operate nearly every modern machine

• microwave ovens, cars, and computers. In an

electronic circuit, an electric signal carries information.

Signals are controlled and changed by components

made from materials called. SEMICONDUCTORS.

A semiconductor is a material that

conducts electricity less well than a metal,

but better than an insulator, and can act

as both a conductor and an insulator. The

chemical elements silicon and germanium

are the most important semiconductors for

making electronic components.

HOW DOES A SEMICONDUCTOR

CONDUCT ELECTRICITY?

The current in a semiconductor is carried by positive

holes and by negative electrons. A hole is an empty

space left in the orbit of an atom when an electron

has escaped. Holes move through a semiconductor in

the opposite direction to electrons, hopping from atom

to atom.

WHAT ARE ELECTRONIC COMPONENTS?

Electronic circuits use components (parts) to control

electric signals. These include resistors, capacitors,

diodes, and transistors. Resistors control how much

current flows through them, capacitors store electric

charges and release them when necessary, and diodes

let current pass through in only one direction.

WHAT IS AN ELECTRIC SIGNAL?

A signal is a current or voltage change that carries

information. Changes can represent instructions,

numbers, sounds, or pictures in the form of a code.

A digital signal is either on or off. An analogue signal

is continuously flowing electricity, which increases

and decreases to represent the information.

WHAT IS A TRANSISTOR?

Transistors are electronic components that can

change and control electronic signals. A transistor

can work as a switch – turning a signal on or off,

or as an amplifier – increasing the current or voltage

in a circuit.

4 RADIO

This colourful X-ray picture shows the electronic components of a radio

through its casing. The radio receives radio waves from a radio station,

translates them into an electric current, and then turns them into

sounds, which are produced by its loudspeaker.

Electronics

SEMICONDUCTORS

Connecting

wires

Volume

control

Loudspeaker

gives out sound

Microchip

Capacitors store

high voltages

Printed circuit board

electronics