Chapter 11: Circuits and Electronics 389

VOCABULARYelectronic p. 389binary code p. 390digital p. 390analog p. 392computer p. 393

BEFORE, you learned

• Charge flows in a closed loop• Circuits are designed for

specific purposes• Electrical appliances use circuits

NOW, you will learn

• How information can be coded• How computer circuits use

digital information• How computers work

KEY CONCEPT

Electronic technologyis based on circuits.

EXPLORE Codes

How can information be coded?

PROCEDURE

Write the numbers 1 to 26 in your note-book. Below each number, write a letter ofthe alphabet. This will serve as your key.

On a separate piece of paper, write thename of the street you live on using numbers instead of words. For each letterof the word, use the number that is directlyabove it on your key.

Exchange messages with a partner and useyour key to decode your partner’s information.

WHAT DO YOU THINK?• How can information be coded?• Under what types of circumstances would information need to be coded?

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MATERIALS• notebook• small piece of

paper

Electronics use coded information.A code is a system of symbols used to send a message. Language is acode, for example. The symbols used in written language are lines andshapes. The words on this page represent meanings coded into the formof letters. As you read, your brain decodes the lines and shapes thatmake up each word, and you understand the message that is encoded.

An device is a device that uses electric current to represent coded information. In electronics, the signals are variationsin the current. Examples of electronic devices include computers,calculators, CD players, game systems, and more.

check your reading Describe the signals used in electronic devices.

electronicRESOURCE CENTERCLASSZONE.COM

Find out more aboutelectronics.

Sunshine StateSTANDARDSSC.H.3.3.4: The studentknows that technologi-cal design shouldrequire taking intoaccount constraintssuch as natural laws,the properties of thematerials used, andeconomic, political,social, ethical, and aesthetic values.

Binary CodeThe English alphabet contains only 26 letters, yet there is no limit tothe number of messages that can be expressed with it. That is becausethe message is conveyed not only by the letters that are chosen butalso by the order in which they are placed.

Many electronic devices use a coding system with only two choices, as compared with the 26 in the alphabet. A coding system

consisting of two choices is a As with alanguage, complex messages can be sent using binarycode. In electronics, the two choices are whether anelectric current is on or off. Switches in electronic circuits turn the current on and off. The result is a message represented in pulses of current.

It may be hard to imagine how something as com-plex as a computer game can be expressed with pulses ofcurrent. But it is a matter of breaking down informationinto smaller and smaller steps. You may have played thegame 20 questions. In that game, you receive a messageby asking someone only yes-or-no questions. The playeranswering the questions conveys the message only inyes’s and no’s, a binary code.

The diagram on the left shows how a decision-makingprocess can be written in simple steps. The diagram issimilar to a computer program, which tells a computerwhat to do. Each step of the process has been brokendown into a binary question. If you determine exactlywhat you mean by cold and hot, then anyone using thisprogram—or even a computer—would arrive at thesame conclusion for a given set of conditions.

check your reading How can a process be broken down into simple steps?

Digital InformationYou can think of the yes-or-no choices in a binary system as being represented by the numbers 0 and 1. Information that is represented asnumbers, or digits, is called information. In electronics, a circuitthat is off is represented by 0, and a circuit that is on is represented by 1.

Digital information is represented in long streams of digits. Each 0 or 1 is also known as a bit, which is short for binary digit. A groupof 8 bits is known as a byte. You might have heard the term gigabyte inreference to the amount of information that can be stored on a com-puter. One gigabyte is equal to about 1 billion bytes. That’s 8 billion 0s and 1s!

digital

binary code.

390 Unit 3: Electricity and Magnetism

Should I wear ajacket?

Is it raining?

Is it cold outside?

Is it hot outside?

Wear a lightjacket.

Wear a raincoat.

Wear a warm coat.

Wear no jacket.

no

yes

yes

yes

no

no

How can you save a drawing in 1s and 0s?PROCEDURE

Draw a 10-square by 10-square grid on a piece of graph paper.

Fill in some of the squares of the grid to draw a picture or pattern. Look atthe example shown, but draw your own picture.

Starting in the upper left-hand corner of your grid, write 0 for every blanksquare and 1 for every filled-in square. Write a continuous series of 1s and 0sfor all rows.

Exchange coded information with a partner who has not seen your picture. Draw a new grid in your notebook and fill it in using your partner’s information.

WHAT DO YOU THINK?• How were you able to reproduce your partner’s picture?

• How is this activity similar to saving an image on a computer?

CHALLENGE Suppose you used three colored markers in your drawing—red, yellow, and green. How could you represent your color drawing using only 1s and 0s?

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Digital InformationDigital InformationSKILLMaking models

MATERIALS• graph paper• plain paper

TIME30 minutes

Chapter 11: Circuits and Electronics 391

Computers, digital cameras, CD players, DVD players, andother devices use digital information. Digital information isused in electronic devices more and more. There are at leasttwo reasons for this:

• Digital information can be copied many times withoutlosing its quality. The 1s are always copied as 1s, and the0s are always copied as 0s.

• Digital information can be processed, or worked with, oncomputers.

For example, a photograph taken on a digital camera can beinput to a computer in the form of digital information. Oncethe photograph is on a computer, the user can modify it, copyit, store it, and send it.

Many portable devices such as game systems and MP3players can also be used with computers. Because computersand the devices use the same type of information, computerscan be used to add games, music, and other programs to thedevices. The photograph at right of a watch shows an example of a portable device that uses digital information.

check your reading Why is digital information often used in electronic devices?

This watch also functionsas an MP3 player—it canstore songs as digital files.

Analog to DigitalSome electronic devices use a system of coding electric current thatdiffers from the digital code. Those electronics use analog information.

information is information that is represented in a continuousbut varying form.

For example, a microphone records sound waves as analog infor-mation. The analog signal that is produced varies in strength as thesound wave varies in strength, as shown below. In order for the signalto be burned onto a CD, it is converted into digital information.

The sound waves are recorded in the microphone as an analogelectrical signal.

The signal is sent through a computer circuit that measures,or samples, each part of the wave. The signal is sampled manythousands of times every second.

Each measurement of the wave is converted into a stream of digits.Microscopic pits representing the stream of digits are burned ontothe CD. A stereo converts the signal from digital back to analogform, making it possible for people to hear what was recorded.

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Analog

392 Unit 3: Electricity and Magnetism

0000

1011

0000

1101

0001

0000

0001

0100

0001

0110

0001

0101

0001

0011

0001

0000

0000

1101

0000

1011

0000

1010

0000

1011

Sound is recorded as an analog signal and convertedto digital information for storage on a CD.

Analog and Digital Signals

analogsignal

digitalsignal

CD burner

pit

The sound waveis recorded as ananalog signal.

1Each part of the analogsignal is converted into aset of binary digits.

2The stream of digits isburned onto the CD. Thepits represent a stream of 1s,and the areas between thepits represent a stream of 0s.

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surfaceof CD

What part of the illustration shows analog information? Whatpart shows digital information?

Computer circuits process digitalinformation.

A is an electronic device that processes digital information.Computers have been important in science and industry for a longtime. Scientists use computers to gather, store, process, and share scientific data. As computers continue to get faster, smaller, and lessexpensive, they are turning up in many places.

Suppose you get a ride to the store. If the car you’re riding in is anewer car, it probably has a computer inside it. At the store, you buy abattery, and the clerk records the sale on a register that is connected toa computer. You put the battery in your camera and take a picture,and the camera has a computer inside it.

Integrated CircuitsThe first digital computer weighed 30 tons and took up a whole room.After 60 years of development, computers the size of a postage stampare able to complete the same tasks in less time. New technology incomputer circuits has led to very small and powerful computers.

Computers process information on circuits that contain manyswitches, branches, and other elements that allow for a very fine control of current. An integrated circuit is a miniature electronic circuit. Tiny switches, called transistors, in these circuits turn off andon rapidly, signaling the stream of digits that represent information.Over a million of these switches may be on one small integrated circuit!

Check Your Reading How do integrated circuits signal digital information?

Most integrated circuits are made from silicon, an elementthat is very abundant in Earth’s crust. When silicon is treatedwith certain chemicals, it becomes a good semiconductor.A semiconductor is a material that is more conductive than an insulator but less conductive than a conductor.Silicon is a useful material in computers becausethe flow of current in it can be finely controlled.

Microscopic circuits are etched onto treated silicon with chemicals or lasers.Transistors and other circuit parts are constructed layer by layer on the silicon.A small, complex circuit on a single piece of silicon is known as a silicon chip, ormicrochip.

computer

This integrated circuit issmaller than the commonant, Camponotus pennsyl-vanicus, which ranges inlength from 6 to 17 mm.

Chapter 11: Circuits and Electronics 393

VOCABULARYRemember to make aframe game diagram for computer.

Personal ComputersWhen you think of a computer, you probably think of a monitor,mouse, and keyboard—a personal computer (PC). All of the physicalparts of a computer and its accessories are together known as hardware.Software refers to the instructions, or programs, and languages thatcontrol the hardware. The hardware, software, and user of a computerall work together to complete tasks.

check your reading What is the difference between hardware and software?

Computers have two kinds of memory. As the user is working,information is saved on the computer’s random-access memory, orRAM. RAM is a computer’s short-term memory. Most computershave enough RAM to store billions of bits. Another type of memory is called read-only memory, or ROM. ROM is a computer’s long-termmemory, containing the programs to start and run the computer.ROM can save information even after a computer is turned off.

The illustration below shows how a photograph is scanned,modified, and printed using a personal computer. The steps fall intofour main functions—input, storage, processing, and output.

394 Unit: Electricity and Magnetism394 Unit: Circuits

OUTLINEUse an outline to takenotes about personal computers.

I . Main idea

A. Supporting idea

1. Detail

2. Detail

B. Supporting idea

394 Unit: Circuits394 Unit 3: Electricity and Magnetism

How a PC Works

0 0 1 1 0 1 1 00 0 0 0 0 0 0 00 0 0 1 1 0 1 1

code for this pixel:

Storage The image isstored as digital infor-mation on the harddrive in the computer.

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computer

Digital information can move through input,processing, storage, and output devices.

Input In the scanner, theimage is broken downinto pixels. Each pixel istranslated into a series ofdigits representing a color.

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VISUALIZATIONCLASSZONE.COM

See how hard drivesstore information.

Input The user scans the photograph on a scanner. Each smallarea, or pixel, of the photograph is converted into a stream ofdigits. The digital information representing the photograph is sentto the main computer circuit, which is called the central processingunit, or CPU.

Storage The user saves the photograph on a magnetic storagedevice called the hard drive. Small areas of the hard drive are magnetized in one of two directions. The magnetized areas oriented in one direction represent 1s, and the areas oriented inthe opposite direction represent 0s, as a way to store the digitalinformation.

Processing The photograph is converted back into pixels on themonitor, or screen, for the user to see. The computer below has asoftware program installed for altering photographs. The user addsmore input to the computer with the mouse and the keyboard toimprove the photograph.

Output The user sends the improved photograph to a printer.The printer converts the digital information back to pixels, and the photograph is printed.

Check Your Reading During which one of the four main computer functions is information converted into digital information?

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Chapter 2: Circuits and Electronics 395Chapter 2: Circuits and Electronics 395Chapter 2: Circuits and Electronics 395Chapter 2: Circuits and Elements 395

How has the photograph of the girl been alteredon the computer?

monitor printer

Processing Theimage is alteredusing software onthe computer.

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Output Digitalinformation istranslated backinto pixels andthe photograph is printed.

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Chapter 11: Circuits and Electronics 395

Computers can be linked with othercomputers.

You may have been at a computer lab or a library and had to wait for aprinter to print something for you. Offices, libraries, and schools oftenhave several computers that are all connected to the same printer.A group of computers that are linked together is known as a network.Computers can also be linked with other computers to share informa-tion. The largest network of computers is the Internet.

The Origin of the InternetPeople have been using computer networks to share information onuniversity campuses and military bases for decades. The computerswithin those networks were connected over telephone systems fromone location to another. But those networks behaved like a series circuit.If the link to one computer was broken, the whole network of linkswent down.

The network that we now call the Internet is different. The UnitedStates Department of Defense formed the Internet by linking computerson college campuses across the country. Many extra links were formed,producing a huge web of connected computers. That way, if somelinks are broken, others still work.

check your reading How does the Internet differ from earlier networks?

The Internet TodayThe Internet now spans the world. E-mail uses the Internet. E-mail hasadded to the ways in which people can “meet,” communicate, conductbusiness, and share stories. The Internet can also be used to work ontasks that require massive computing power. For example, millions ofcomputers linked together, along with their combined information,might one day be used to develop a cure for cancer or model theworkings of a human mind.

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This map shows a repre-sentation of Internettraffic in the early 1990s.A map of Internet trafficnow would be even morefull of lines.

When you think of the Internet, you might think of the WorldWide Web, or the Web. The Web consists of all of the information thatcan be accessed on the Internet. This information is stored on millionsof host computers all over the world. The files that you locate arecalled Web pages. Each Web page has an address that begins withwww, which stands for World Wide Web. The system allows you tosearch or surf through all of the information that is available on it.You might use the Web to research a project. Millions of people usethe Web every day to find information, to shop, or for entertainment.

You may have heard of the Bronze Age or the Iron Age inyour history class. Digital information and the Internet havehad such a strong impact on the way we do things that somepeople refer to the era we live in as the Information Age.

KEY CONCEPTS1. Describe an example of coded

information.

2. What is digital information?Give three examples of devicesthat use digital information.

3. Give an example of each of the following in terms of computers: input, storage, processing, and output.

CRITICAL THINKING4 Compare Morse code uses a

signal of dots and dashes toconvey messages. How is Morsecode similar to digital code?

5. Infer The word integratedmeans “brought together toform a whole.” How does that definition apply to an integrated circuit?

CHALLENGE6. Predict Computers as we

know them did not exist 50years ago, and now they areused for many purposes. Howdo you think people will usecomputers 50 years from now?Write a paragraph describingwhat you think the computersof the future will be like andhow they will be used.

Chapter 11: Circuits and Electronics 397

Internet Usage

SOURCE: Internet Software Consortium (http://www.isc.org)

Year

Hos

t Co

mpu

ters

(in

mill

ions

)80

40

120

160

200

1995 1999 20011997 2003* *projected