Childrens Illustrated Encyclopedia

183

SEMICONDUCTORS

Most electronic components

are made of materials such

as silicon, which are

called semiconductors.

Semiconductors control the

flow of current because they

contain a variable number of

charge carriers (particles that

carry electricity). In n-type

semiconductors, the charge

carriers are negatively

charged electrons; in p-type

semiconductors, the charge

carriers are positively charged

“holes”—regions where

electrons are absent.

Electronics

The semiconductor silicon

comes from sand, which is

a compound of silicon

and oxygen.

A diode is made

from the junction

between pieces

of n- and p-type

semiconductors.

CIRCUIT BOARD

An electronic device, such as a telephone,

contains an electronic circuit consisting of
several components joined together on a

circuit board. Every circuit is designed for
a particular task. The circuit in a radio,

for instance, picks up and amplifies
(boosts) radio waves so they can be

converted into sound.

MICROCHIPS

Microchips, or silicon chips, contain circuits consisting

of millions of microscopic components. These circuits

are squeezed onto the surface of a semiconductor less

than 1 in (25 mm) square.

TRANSISTOR

Transistors lie at the heart of most

electronic machines. They boost

current and voltage in amplifier

circuits, store information in

computers, and perform many

other tasks. Physicists William

Shockley, John Bardeen, and

Walter Brattain invented the

transistor in 1947.

ELECTRICITY is a source

of power that drives machines

and provides heat and light.

Electricity is also used to produce

signals that carry information and control devices.

Using electricity in this way is called electronics. We

are surrounded by thousands of electronic machines,

including computers, MP3 players, telephones, and

televisions. All these machines contain circuits through

which electric currents flow. Tiny electronic components

in the circuits control the flow of the current to produce

signals. For instance, a varying current may represent

sound in a telephone line, or a number in a computer.

The most important electronic component is the

transistor. A small radio receiver may contain a

dozen transistors; a computer contains millions

of transistors inside microchips.

If a battery is connected the

other way around, holes

and electrons cannot cross

the junctions so current

cannot flow.

A diode allows current to flow

through it in only one direction.

The current is carried by the

flow of holes and electrons.

CONTROLLING CURRENT

Electronic circuits do several basic jobs.

They may amplify current; they may

produce an oscillating current—one that

rapidly changes direction, essential for

generating radio waves; or

they may switch current on

and off.

Oscillation: Some circuits convert

a steady one-way current (direct

current, or DC) into a varying

alternating current (AC).

Amplification: An amplifier circuit

generates a strong AC current that is an

accurate copy of a weaker AC current.

Switching: In computers, electronic

circuits rapidly switch current on and

off in a code that represents data.

Find out more

Computers

Electricity

Radio

Technology

Television

Small “glue”

chip helps large

chips operate.

Resistor

controls

current.

Transistor

switches

current.

Copper track

(under green

insulation)

connects

components.

Quartz crystal

controls timing.

Electrolytic

capacitor

smooths

current.

Large chip

processes

information.

Voltage

regulator