hst physical science teachers edition · osp lesson plans(also in print) trbellringer transparency*...

UNIT

T I M E L I N E

6

ElectricityCan you imagine a world without computers, motors, or even light bulbs? Your life would be very different indeed without electricity and the devices that depend on it. In this unit, you will learn how electricity results from tiny charged particles, how electricity and mag-netism interact, and how electronic technology has revolutionized the world in a relatively short amount of time. This timeline includes some of the events leading to our current understanding of electricity, electromagne-tism, and electronictechnology.

470 Unit 6

1751Benjamin Franklin

flies a kite to which

a key is attached in

a thunderstorm to

demonstrate that

lightning is a form

of electricity.

1958The invention of the

integrated circuit, which

uses millions of transistors,

revolutionizes electronic

technology.

1903Dutch physician

Willem Einthoven

develops the first

electrocardiograph

machine to record

the tiny electric

currents that pass

through the body’s

tissues.

1947The transistor is invented.

Electricity 471

1911Superconductivity is discovered.

Superconductivity is the ability

some metals and alloys have

to carry electric current with-

out resistance under certain

conditions.

1773American colonists hold

the “Boston Tea Party”

and dump 342 chests of

British tea into Boston

Harbor.

1831British scientist Michael

Faraday and American

physicist Joseph Henry

separately demonstrate

the principle of electro-

magnetic induction in

which magnetism is used

to generate electricity.

1945Grace Murray Hopper, a pioneer

in computers and computer

languages, coins the phrase

“debugging the computer” after

removing from the wiring of her

computer a moth that caused

the computer to fail.

1984The first portable CD

player is introduced.

2003One of the largest electricity

blackouts in North American

history started in the after-

noon on August 14, 2003. The

blackout left several large cities,

including New York City; Detroit,

Michigan; and Toronto, Canada,

in the dark. Several days passed

before electrical energy was

fully restored to the millions of

people affected in eight U.S.

states and Canada.

Garry Kasparov, reigning

world chess champion,

loses a historic match to a

computer named Deep Blue.

1997

The telephone is

officially invented by

Alexander Graham

Bell, who beats

Elisha Gray to the

patent office by only

a few hours.

1876

OBJECTIVES LABS, DEMONSTRATIONS, AND ACTIVITIES TECHNOLOGY RESOURCES

Compression guide:To shorten instructionbecause of time limitations,omit Section 3.

Online and Technology Resources

Visit go.hrw.com foraccess to Holt OnlineLearning, or enter thekeyword HP7 Homefor a variety of freeonline resources.

This CD-ROM package includes:• Lab Materials QuickList Software• Holt Calendar Planner• Customizable Lesson Plans• Printable Worksheets

• ExamView® Test Generator• Interactive Teacher’s Edition• Holt PuzzlePro®

• Holt PowerPoint® Resources

17 Introduction to ElectricityChapter Planning Guide

Chapter Opener

471A Chapter 17 • Introduction to Electricity

OSP Lesson Plans (also in print) TR Bellringer Transparency* TR P67 Structure of an Atom* TR P68 Law of Electric Charges* TR P69 How Lightning Forms* CD Interactive Explorations CD-ROM

Tunnel VisiongCD Science Tutor

TE Activity Balloons and Static Electricity, p. 474g TE Activity Exploring Charge, p. 475b SE Quick Lab Detecting Charge, p. 477 ◆g

TE Activity Electron Transfer, p. 477b SE Connection to Social Studies Benjamin Franklin,

p. 480g SE Skills Practice Lab Stop the Static Electricity!,

p. 732 ◆g

LB Whiz-Bang Demonstrations Hoop It Up*a LB Whiz-Bang Demonstrations Bending Water*a

Section 1 Electric Charge and Static Electricity• Describe how charged objects interact by using the

law of electric charges.• Describe three ways in which an object can become

charged.• Compare conductors with insulators.• Give two examples of static electricity and electric

discharge.

OSP Lesson Plans (also in print) TR Bellringer Transparency* TR P70 How a Cell Produces an Electric

Current* TR LINK TOLINK TO LIFE SCIENCE LIFE SCIENCE L90 What Is a

Nerve?* SE Internet Activity, p. 488gCD Science Tutor

SE Connection to Biology Help for a Heart, p. 485g TE Group Activity Modeling Resistance, p. 486g TE Activity Lemon Cells, p. 487 ◆a

SE Model-Making Lab Potato Power, p. 733 ◆b

CRF Datasheet for LabBook* LB Calculator-Based Labs Lemon “Juice”*a

PACING • 45 min pp. 482–489Section 2 Electric Current and Electrical Energy• Describe electric current.• Describe voltage and its relationship to electric current.• Describe resistance and its relationship to electric

current.• Explain how a cell generates electrical energy.• Describe how thermocouples and photocells

generate electrical energy.

OSP Lesson Plans (also in print) TR Bellringer Transparency*CD Science Tutor

TE Demonstration Current and Amps, p. 490b TE Connection Activity Math, p. 491g SE School-to-Home Activity Saving Energy, p. 493g SE Science in Action Math, Social Studies, and Language

Arts Activities, pp. 506–507g

PACING • 45 min pp. 490–493Section 3 Electrical Calculations• Use Ohm’s law to calculate voltage, current, and

resistance.• Calculate electric power.• Determine the electrical energy used by a device.

OSP Lesson Plans (also in print) TR Bellringer Transparency* TR P71 Parts of a Circuit*CRF SciLinks Activity*gVID Lab Videos for Physical ScienceCD Science Tutor

TE Demonstration Circuit Building, p. 494 ◆g

TE Connection Activity Language Arts, p. 494g SE Quick Lab A Series of Circuits, p. 496 ◆g

SE Quick Lab A Parallel Lab, p. 497 ◆g

TE Group Activity Concept Mapping, p. 497g SE Skills Practice Lab Circuitry 101, p. 500 ◆g

LB Long-Term Projects & Research Ideas The Future IsElectric*a

PACING • 90 min pp. 494–499Section 4 Electric Circuits• Name the three essential parts of a circuit.• Compare series circuits with parallel circuits.• Explain how fuses and circuit breakers protect your

home against short circuits and circuit overloads.

OSP Parent Letter ■

CD Student Edition on CD-ROM CD Guided Reading Audio CD ■

TR Chapter Starter Transparency*VID Brain Food Video Quiz

SE Start-up Activity, p. 473gpp. 472–481PACING • 90 min

CRF Vocabulary Activity*g SE Chapter Review, pp. 502–503g

CRF Chapter Review* ■g

CRF Chapter Tests A* ■g, B*a, C*s SE Standardized Test Preparation, pp. 504–505g

CRF Standardized Test Preparation*gCRF Performance-Based Assessment*gOSP Test Generator, Test Item Listing

CHAPTER REVIEW, ASSESSMENT, ANDSTANDARDIZED TEST PREPARATION

PACING • 90 min

STANDARDS CORRELATION SKILLS DEVELOPMENT RESOURCES SECTION REVIEW AND ASSESSMENT CORRELATIONS

Maintained by the NationalScience Teachers Association.See Chapter Enrichment pagesthat follow for a complete listof topics.

www.scilinks.orgCheck out Current Sciencearticles and activities byvisiting the HRW Web siteat go.hrw.com. Just typein the keyword HP5CS17T.

• Lab Videos demonstratethe chapter lab.

• Brain Food Video Quizzeshelp students review thechapter material.

ClassroomVideos

Holt Lab GeneratorCD-ROM

Search for any lab by topic, standard,difficulty level, or time. Edit any labto fit your needs, or create your ownlabs. Use the Lab Materials QuickListsoftware to customize your labmaterials list.

• Guided Reading Audio CD(Also in Spanish)

• Interactive Explorations• Virtual Investigations• Visual Concepts• Science Tutor

ClassroomCD-ROMs

Chapter 17 • Chapter Planning Guide 471B

CRF Directed Reading A* ■b, B*s IT Interactive Textbook* Struggling ReadersStruggling Readers

CRF Vocabulary and Section Summary* ■g

SE Reading Strategy Reading Organizer, p. 474g TE Support for English Language Learners, p. 476 SE Connection to Environmental Science Painting Cars, p. 476g TE Reading Strategy Prediction Guide, p. 476b

CRF Reinforcement Worksheet Charge!*b

SE Reading Checks, pp. 474, 476, 477, 479,480g

TE Homework, p. 478g TE Reteaching, p. 480b TE Quiz, p. 480g TE Alternative Assessment, p. 480g SE Section Review,* p. 481 ■g

CRF Section Quiz* ■g

UCP 2; SPSP 3, 5; HNS 3; PS3a; LabBook: UCP 2; SAI 1, 2;PS 3a, 3d



SE Reading Strategy Reading Organizer, p. 482g TE Inclusion Strategies, p. 483 TE Support for English Language Learners, p. 483 TE Reading Strategy Prediction Guide, p. 485g

SE Reading Checks, pp. 482, 483, 484, 487,488g

TE Reteaching, p. 488b TE Quiz, p. 488g TE Alternative Assessment, p. 488g SE Section Review,* p. 489 ■ g

CRF Section Quiz* ■g

SPSP 5; PS 3a; LabBook: UCP 2;SAI 1, 2; PS 3a



SE Reading Strategy Paired Summarizing, p. 490g SE Math Focus Using Ohm’s Law, p. 491g TE Support for English Language Learners, p. 491 SE Math Focus Power and Energy, p. 492g MS Math Skills for Science Multiplying Whole Numbers*g

SE Reading Checks, pp. 491, 492g TE Reteaching, p. 492b TE Quiz, p. 492g SE Section Review,* p. 493 ■ g

TE Alternative Assessment, p. 493gCRF Section Quiz* ■ g

HNS 3; PS 3a



SE Reading Strategy Brainstorming, p. 494g SE Connection to Biology Nervous Impulses, p. 495g TE Inclusion Strategies, p. 495 TE Support for English Language Learners, p. 496

CRF Reinforcement Worksheet Electric Circuits*bCRF Critical Thinking Potentially Shocking!*a

SE Reading Checks, pp. 494, 495, 496, 497, 498g TE Homework, p. 497g TE Reteaching, p. 498b TE Quiz, p. 498g TE Alternative Assessment, p. 498g SE Section Review,* p. 499 ■ g

CRF Section Quiz* ■ g

SPSP 5; PS 3d; Chapter Lab:UCP 2; SAI 1, 2; PS 3a, 3d

SE Pre-Reading Activity, p. 472gOSP Science Puzzlers, Twisters & Teasersg

National ScienceEducation Standards

UCP 5; SAI 1, 2

CRF Chapter Resource File SS Science Skills Worksheets IT Interactive TextbookOSP One-Stop Planner MS Math Skills for Science Worksheets * Also on One-Stop Planner

SE Student Edition LB Lab Bank CD CD or CD-ROM ◆ Requires advance prepTE Teacher Edition TR Transparencies VID Classroom Video/DVD ■ Also available in Spanish

KEY

Planning ResourcesTEST ITEM LISTINGPARENT LETTERLESSON PLANS

Visual ResourcesCHAPTER STARTER

TRANSPARENCYBELLRINGER

TRANSPARENCIES

CONCEPT MAPPING TRANSPARENCYTEACHING TRANSPARENCIES

TEACHING TRANSPARENCIES

TEST ITEM LISTING

Copyright © by Holt Rinehart and Winston All rights reserved

The World of ScienceMULTIPLE CHOICE

1. A limitation of models is thata. they are large enough to see.b. they do not act exactly like the things that they model.c. they are smaller than the things that they model.d. they model unfamiliar things.Answer: B Difficulty: I Section: 3 Objective: 2

2. The length 10 m is equal toa. 100 cm. c. 10,000 mm.b. 1,000 cm. d. Both (b) and (c)Answer: B Difficulty: I Section: 3 Objective: 2

3. To be valid, a hypothesis must bea. testable. c. made into a law.b. supported by evidence. d. Both (a) and (b)Answer: B Difficulty: I Section: 3 Objective: 2 1

4. The statement "Sheila has a stain on her shirt" is an example of a(n)a. law. c. observation.b. hypothesis. d. prediction.Answer: B Difficulty: I Section: 3 Objective: 2

5. A hypothesis is often developed out ofa. observations. c. laws.b. experiments. d. Both (a) and (b)Answer: B Difficulty: I Section: 3 Objective: 2

6. How many milliliters are in 3.5 kL?a. 3,500 mL c. 3,500, 000 mLb. 0.0035 mL d. 35,000 mLAnswer: B Difficulty: I Section: 3 Objective: 2

7. A map of Seattle is an example of aa. law. c. model.b. theory. d. unit.Answer: B Difficulty: I Section: 3 Objective: 2

8. A lab has the safety icons shown below. These icons mean that you should weara. only safety goggles. c. safety goggles and a lab apron.b. only a lab apron. d. safety goggles, a lab apron, and gloves.Answer: B Difficulty: I Section: 3 Objective: 2

9. The law of conservation of mass says the tot al mass before a chemical change isa. more than the total mass after the change.b. less than the total mass after the change.c. the same as the total mass after the change.d. not the same as the total mass after the change.Answer: B Difficulty: I Section: 3 Objective: 2

10. In which of the following areas might you find a geochemist at work?a. studying the chemistry of rocks c. studying fishesb. studying forestry d. studying the atmosphereAnswer: B Difficulty: I Section: 3 Objective: 2

TEACHER RESOURCE PAGE

Lesson Plan

Section: Waves

PacingRegular Schedule: with lab(s): 2 days without lab(s): 2 days

Block Schedule: with lab(s): 1 1/2 days without lab(s): 1 day

Objectives1. Relate the seven properties of life to a living organism.

2. Describe seven themes that can help you to organize what you learn aboutbiology.

3. Identify the tiny structures that make up all living organisms.

4. Differentiate between reproduction and heredity and between metabolismand homeostasis.

National Science Education Standards CoveredLSInter6: Cells have particular structures that underlie their functions.

LSMat1: Most cell functions involve chemical reactions.

LSBeh1:Cells store and use information to guide their functions.

UCP1:Cell functions are regulated.

SI1: Cells can differentiate and form complete multicellular organisms.

PS1: Species evolve over time.

ESS1: The great diversity of organisms is the result of more than 3.5 billion yearsof evolution.

ESS2: Natural selection and its evolutionary consequences provide a scientificexplanation for the fossil record of ancient life forms as well as for the strikingmolecular similarities observed among the diverse species of living organisms.

ST1: The millions of different species of plants, animals, and microorganismsthat live on Earth today are related by descent from common ancestors.

ST2: The energy for life primarily comes from the sun.

SPSP1: The complexity and organization of organisms accommodates the needfor obtaining, transforming, transporting, releasing, and eliminating the matterand energy used to sustain the organism.

SPSP6: As matter and energy flows through different levels of organization ofliving systems—cells, organs, communities—and between living systems and thephysical environment, chemical elements are recombined in different ways.

HNS1: Organisms have behavioral responses to internal changes and to externalstimuli.

This CD-ROM includes all of the resources shown here and the following time-saving tools:

• Lab Materials QuickList Software

• Customizable lesson plans

• Holt Calendar Planner

• The powerful ExamView ® Test Generator

Chapter Resources

Dear Parent,

Your son's or daughter's science class will soon begin exploring the chapter entitled “The

World of Physical Science.” In this chapter, students will learn about how the scientific

method applies to the world of physical science and the role of physical science in the

world. By the end of the chapter, students should demonstrate a clear understanding of the

chapter’s main ideas and be able to discuss the following topics:

1. physical science as the study of energy and matter (Section 1)

2. the role of physical science in the world around them (Section 1)

3. careers that rely on physical science (Section 1)

4. the steps used in the scientific method (Section 2)

5. examples of technology (Section 2)

6. how the scientific method is used to answer questions and solve problems (Section 2)

7. how our knowledge of science changes over time (Section 2)

8. how models represent real objects or systems (Section 3)

9. examples of different ways models are used in science (Section 3)

10. the importance of the International System of Units (Section 4)

11. the appropriate units to use for particular measurements (Section 4)

12. how area and density are derived quantities (Section 4)

Questions to Ask Along the Way

You can help your son or daughter learn about these topics by asking interesting questions

such as the following:

• What are some surprising careers that use physical science?

• What is a characteristic of a good hypothesis?

• When is it a good idea to use a model?

• Why do Americans measure things in terms of inches and yards instead of centimeters

and meters ?

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Co

mm

un

ication

and

Co

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AN

SPAR

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What Is a N

erve?Spinal cord

Nerve

Axon

Muscle

fiber

Axon

terminal

A m

essage from the brain travels

down the spinal cord, then along the axon of

a motor neuron inside a nerve to the m

uscle. The m

essage makes the m

uscle contract.

e

471C Chapter 17 • Introduction to Electricity

17

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Introduction to Electricity TEACHING TRANSPARENCY

Parts of a Circuit

Wires connect the other parts of a circuit. Wires are made of conducting materials that have low resist-ance, such as copper.

The energy sourcecan be a battery, a photocell, a thermo-couple, or an electric generator at a power plant.

Examples of loads arelight bulbs, appliances, televisions, and motors.

Cop

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ht ©

by

Hol

t, R

ineh

art

and

Win

ston

. All

righ

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eser

ved.

Introduction to Electricity TEACHING TRANSPARENCY

Law of Electric Charges

Objects that have the same charge repel each other. Each object exerts a force on the other object. These forces push the objects apart.

Objects that have opposite charges are attracted to each other. Each object exerts a force on the other object. These forces pull the objects together.

Chapter: Communication and Control

Introduction of Electricity CHAPTER STARTER

The most shocking of all fish tales con-cerns the electric eel, a freshwater fish ofCentral America and South America thatcan produce powerful jolts of electricalenergy. Electric discharges from this 2.5 mlong creature are strong enough to stunand kill smaller fish and frogs in the water.The eel can then swallow its motionlessprey whole. Early travelers to the AmazonRiver basin wrote that, in shallow pools,the eels’ electric discharges could knockhorses and humans over.

How does the electric eel perform itsshocking feat? Within this fish’s long bodyare a series of electroplates—modifiedmuscle tissues that generate low voltages.The electricity produced by one wafer-thinelectroplate is small. But eels have 5,000to 6,000 electroplates connected togetherand can therefore produce a high voltage.In laboratory experiments, the bursts ofvoltage from a fully grown eel have beenmeasured at around 600 volts. That’s five

times the voltage of an electrical outlet—all from the cells of a single fish! The eel’sthick, leathery skin prevents the eel fromelectrocuting itself while zapping prey.

Now that you know what one amazingfish can do with electricity, read on tolearn what people have accomplishedwith this versatile form of energy.


Strange but True!

Introduction to Electricity BELLRINGER TRANSPARENCY


Section: Electric Charge and Static ElectricityWrite a definition for electric charge in your ownwords in your science journal. When do youexperience electric charges most, in winter or insummer? Explain your reasoning.

Section: Electric Current and Electrical EnergyWhat is the difference between something that isdirect and something that is alternating? How doesthe difference relate to electric current?

Record your responses in your science journal.


Intro

du

ction

to Electricity

TEACH

ING

TRA

NSPA

REN

CY

Structure of an Atom

Nucleus

Electron

Proton

Neutron

ronsterof


Intro

du

ction

to Electricity

TEACH

ING

TRA

NSPA

REN

CY

How Lightning Form

s

The negative charge at the bottom of the

cloud may induce a positive charge on the

ground. The large charge difference causes a rapid electric discharge called lightning.

b

During a thunderstorm

, water drop-

lets, ice, and air move inside the

storm cloud. A

s a result, negative charges build up, often at the bottom

of the cloud. Positive charges often build up at the top.

a

Different parts of clouds

have different charges. In fact, m

ost lightning happens w

ithin and between clouds.

c


Intro

du

ction

to Electricity

TEACH

ING

TRA

NSPA

REN

CY

How a Cell Produces an Electric CurrentFlo

w

A chem

ical reaction with the

electrolyte leaves extra elec-trons on one electrode. This electrode is m

ade of zinc.

a

A different chem

ical reaction causes electrons to be pulled off the other electrode. In this cell, this electrode is m

ade of copper.

b

If the electrodes are con-nected by a w

ire, electrons flow

through the wire and

ions move in the electrolyte.

The moving charges m

ake an electric current.

c

from from chemical energy

photocell

is generated by a

from

Introduction to Electricity CONCEPT MAPPING TRANSPARENCY


Use the following terms to complete the concept map below:battery, electrical energy, thermocouple, light energy, thermal energy

SAMPLE SAMPLE SAMPLE

Meeting Individual Needs

Review and Assessments

Labs and Activities

DIRECTED READING A VOCABULARY ACTIVITY REINFORCEMENT

STANDARDIZED TEST PREPARATIONCHAPTER TEST BCHAPTER REVIEWSECTION QUIZ

SCILINKS ACTIVITY

MARINE ECOSYSTEMS

Go to www.scilinks.com. To find links relatedto marine ecosystems, type in the keywordHL5490. Then, use the links to answer thefollowing questions about marine ecosys-tems.

1. What percentage of the Earth’s surface iscovered by water?

2. What percentage of the Earth’s water is found in the oceans?

3. What is the largest animal on Earth?

4. Describe an ocean animal.

Name Class Date

SciLinks ActivityActivity

Developed and maintained by theNational Science Teachers Association

Topic: Reproductive SystemIrregularitiesSciLinks code: HL5490

WHIZ-BANGDEMONSTRATIONS


Name Class Date

Vocabulary ActivityActivity

Getting the Dirt on the SoilAfter you finish reading Chapter: [Unique Title], try this puzzle! Use the clues belowto unscramble the vocabulary words. Write your answer in the space provided.

1. the breakdown of rock intosmaller and smaller pieces:AWERIGNETH

2. layer of rock lying beneath soil:CROKDEB

3. type of crop that is plantedbetween harvests to reduce soilerosion: CROVE

4. action of rocks and sedimentscraping against each other andwearing away exposed surfaces:SABRONIA

5. a mixture of small mineral frag-ments and organic matter: LISO

6. rock that is a source of soil:PRATEN CORK

7. type of reaction that occurs whenoxygen combines with iron toform rust: oxidation

8. type of weathering caused byphysical means: CLEMANIACH

9. the chemical breakdown of rocksand minerals into new substances: CAMILCHETHEARIGWEN

10. layers of soil, to a geologist:SNORHIZO

11. the uppermost layer of soil:SPOTOIL

12. process in which rainwater car-ries dissolved substances fromthe uppermost layers of soil to thebottom layers: HELANCIG

13. small particles of decayed plantand animal material in soil:MUUSH

14. the process in which wind, water,or ice moves soil from one location to another: ROOSINE

15. the methods humans use to takecare of soil:OSIL VASETONRICON

LONG-TERM PROJECTS & RESEARCH IDEAS CALCULATOR-BASED LABS

DATASHEETS FOR QUICKLABS

DATASHEETS FOR QUICK LABS

VOCABULARY AND SECTION SUMMARY


Section: EnergIn the space provided, write the letter of the description that best matches theterm or phrase.

______ 1. building molecules that can be used asan energy source. or breaking down moleculesin which energy is stored

______ 2. the process by which light energy is convertedto chemical energy

______ 3. an organism that uses sunlight or inorganicsubstances to make organic compounds

______ 4. an organism that uses sunlight or inorganicsubstances to make organic compounds

______ 5. an organism that consumes food to get energy

______ 6. the process of getting energy from food

In the space provided, write the letter of the term or phrase that best completeseach statement or best answers each question.

Name Class Date

Section QuizAssessment

a. photosynthesis

b. autotroph

c. heterotroph

d. cellular respiration

e. metabolism

f. cellular respiration

______ 7. Which of the following mostclosely resembles cellularrespiration?a. warm water moving

through copper pipesb. people movimg alomg a

escalatorc. mixing different foods in

a blenderd. logs burning in a fire

______ 8. An organism’s reproductivecells, such as sperm or eggcells, are called?a. genesb. chromosomesc. gamates.d. zygotes.

______ 9. An organism’s reproductivecells, such as sperm or eggcells, are called?a. genesb. chromosomesc. gamates.d. zygotes.

______10. Which of the following mostclosely resembles cellularrespiration?a. warm water moving

through copper pipesb. people movimg alomg a

escalatorc. mixing different foods in

a blenderd.

logs burning in a fire


Section: ExploringTHAT’S SCIENCE!

1. How did James Czarnowski get his idea for the penguin boat, Proteus?Explain.

2. What is unusual about the way that Proteus moves through the water?

MATTER + AIR ➔ PHYSICAL SCIENCE

3. What do air, a ball, and a cheetah have in common?

4. What is one question you will answer as you explore physical science?

5. Chemistry and physics are both fields of . Chemists

study the different forms of and how they interact.

and how it affects are

studied in physics.

Identify the field of physical science to which each of the following descriptionsbelongs by writing physics or chemistry in the space provided.

_______________________ 6. how a compass works

_______________________ 7. why water boils at 100°C

_______________________ 8. how chlorine and sodium combine to form table salt

_______________________ 9. why you move to the right when the car you are inturns left

Directed Reading A

Name Class Date

Skills Worksheet

DIRECTED READING B

Section: ExploringTHAT’S SCIENCE!

1. How did James Czarnowski get his idea for the penguin boat, Proteus?Explain.

2. What is unusual about the way that Proteus moves through the water?

MATTER + AIR ➔ PHYSICAL SCIENCE

3. What do air, a ball, and a cheetah have in common?

Directed Reading B

Name Class Date

Skills Worksheet

Section: UniqueVOCABULARY

In your own words, write a definition of the following term in the space provided.

1. scientific method

2. technology

3. observation

Name Class Date

Vocabulary & NotesSkills Worksheet

Name Class Date

ReinforcementSkills Worksheet

The Plane TruthComplete this worksheet after you finish reading the Section: [Unique SectionTitle]

You plan to enter a paper airplane contest sponsoredby Talkin’ Physical Science magazine. The personwhose airplane flies the farthest wins a lifetime sub-scription to the magazine! The week before the con-test, you watch an airplane landing at a nearbyairport. You notice that the wings of the airplane haveflaps, as shown in the illustration at right. The paperairplanes you’ve been testing do not have wing flaps.What question would you ask yourself based on these observations? Write yourquestion in the space below for “State the problem.” Then tell how you could usethe other steps in the scientific method to investigate the problem.

1. State the problem.

2. Form a hypothesis.

3. Test the hypothesis.

4. Analyze the results.

5. Draw conclusions.

Flaps


CRITICAL THINKING

A Solar Solution

Name Class Date

Critical Thinking Skills Worksheet

Joseph D. Burns

Inventors’ Advisory Consultants

Portland, OR 97201

Dear Mr. Burns,I’ve got this great idea for a new product called the BlissHeater. It’s a portable, solar-powered space heater. The heater’s design includes these features:•T

he heater will be as longas an adult’s arm and aswide as a

packing box.

•T

he heater will have aglass top set at an angleto catch the sun’s rays.

•T

he inside of the heaterwill be dark colored toabsorb solar heat.If you think my idea will work, I will make the Bliss

Heaters right away without wasting time and money on test-ing and making models. Please write back soon with youropinion.

SECTION REVIEW

Section: UniqueKEY TERMS

1. What do paleontologist study?

2. How does a trace fossil differ from petrified wood?

3. Define fossil.

UNDERSTANDING KEY IDEAS

Name Class Date

Section ReviewSkills Worksheet


[UniqueMULTIPLE CHOICE


______ 1. Surface currents are formed by a. the moon’s gravity. c. wind.b. the sun’s gravity. d. increased water density.

______ 2. When waves come near the shore, a. they speed up. c. their wavelength increases.b. they maintain their speed. d. their wave height increases.

______ 3. Longshore currents transport sediment a . out to the open ocean. c. only during low tide.b. along the shore. d. only during high tide.

______ 4. Which of the following does NOT control surface currents?a. global wind c. Coriolis effectb. tides d. continental deflections

______ 5. Whitecaps break a. in the surf. c. in the open ocean.b. in the breaker zone. d. as their wavelength increases.

______ 6. Most ocean waves are formed by a . earthquakes. c. landsides.b. wind. d. impacts by cosmic bodies.

______ 7. Which factor controls surface currents? a. global winds c. continental deflectionb. the Coriolis effect d. all of the above

______ 8. Streamlike movments of ocean water far below the surface arecalleda. jet currents c. surface currents.b. Coriolis currents. d. deep currents.

______ 9. When the sunlit part of the moon that can be seen from Earthgrows larger, it is a. waxing. c. in the new moon phase.b. waning. d. in the full moon phase.

______10. The Milky Way is thought to be a. an elliptical galaxy. c. a spiral galaxy.

Name Class Date

Chapter Test BAssessment


READING

Read the passages below. Then, read each question that follows the passage.Decide which is the best answer to each question.

Passage 1 adventurous summer camp in the world. Billy can’twait to head for the outdoors. Billy checked the recommendedsupply list: light, summer clothes; sunscreen; rain gear; heavy,down-filled jacket; ski mask; and thick gloves. Wait a minute! Billythought he was traveling to only one destination, so why does heneed to bring such a wide variety of clothes? On further investiga-tion, Billy learns that the brochure advertises the opportunity to“climb the biomes of the world in just three days.” The destinationis Africa’s tallest mountain, Kilimanjaro.

______ 1. The word destination in this passage means A camp B vacation.C place. D mountain.

______ 2. Which of the following is a FACT in the passage? F People ski on Kilimanjaro.G Kilimanjaro is Africa’s tallest mountain.H It rains a lot on Kilimanjaro.J The summers are cold on Kilimanjaro.

______ 3. Billy wondered if the camp was advertising only one destination afterhe read the brochure, which said thatA the camp was the most adventurous summer camp in the world. B he would need light, summer clothes and sunscreen.C he would need light, summer clothes and a heavy, down-filled

jacket.D the summers are cold on Kilimanjaro.

Name Class Date

Standardized Test PreparationAssessment

PERFORMANCE-BASEDASSESSMENT

OBJECTIVEDetermine which factors cause some sugar shapes to break down faster than others.

KNOW THE SCORE!As you work through the activity, keep in mind that you will be earning a gradefor the following:

• how you form and test the hypothesis (30%)

• the quality of your analysis (40%)

• the clarity of your conclusions (30%)

ASK A QUESTIONSWhy do some sugar shapes erode more rapidly than others?

MATERIALS AND EQUIPMENT

Name Class Date

Performanced-Based AssessmentAssessment SKILL BUILDER

Using Scientific Methods

• 1 regular sugar cube • 90 mL of waterCopyright © by Holt, Rinehart and Winston. All rights reserved.

USING VOCABULARY

1. Define biome in your own words.

2. Describe the characteristics of a savanna and a desert.

3. Identify the relationship between tundra and permafrost.

4. Compare the open-water zone and the deep-water zone.

5. Use each of the following terms in an original sentence: plankton, littoralzone, and estuary.

6. Describe how marshes and swamps differ.

Name Class Date

Chapter ReviewSkills Worksheet

SCIENCE PUZZLERS, TWISTERS & TEASERS

CHAPTER TEST A






______ 4. Which of the following does NOT control surface currents?a global wind c Coriolis effect

Name Class Date

Chapter Test AAssessment

CHAPTER TEST C






______ 4. Which of the following does NOT control surface currents?a global wind c Coriolis effect

Name Class Date

Chapter Test CAssessment

Chapter 17 • Chapter Resources 471D

Name _______________________________________________ Date ________________ Class______________

SCIENCE PUZZLERS, TWISTERS & TEASERS17

Introduction to Electricity

CHAPTER

The Power Grid Maze1. In this puzzle, the letters P-O-W-E-R are all conductors, and all X’s

are grounds. All other letters are neutral. A trail comes to a deadend any time one of the “power” letters borders an X. In order to complete the circuit from beginning to end, mark a trail of con-ducting letters that does not lead to a dead end. Power can runhorizontally or vertically but not diagonally.

P O W X E R B A D L Y T X S T U N G T VZ P A B F G H O W R P E E L E P W R O PD E O R C D U N C E F I S H E M Q S T BC R U P R R G R S P E X W O W N V M L ZB P V S T O P W R W O P R W O P O P W RH W X Q N W A C X D P G H A Q F T L K RL J M C D P D X Y U X I F X U A E T V EG D F Y A E D U G Q U I L L A N S W E RH C X X B E L V W E R O P P C G T O T GL I G S L W E T W S U S T R K N O P H FJ K V T A O D V P T N H I R S U T W C G

BEGIN ⇒⇒EXIT

For a preview of available worksheets covering math and science skills, see pages T26–T33. All of these resources are also on the One-Stop Planner®.

If you’ve ever been stuck in traffic with the windows rolled down, you know hownoxious the fumes from a car’s exhaust can be. Not only do the fumes smell bad,but they’re bad for the environment as well. And the fossil fuels that power ourcars and trucks today won’t be around forever. What can we do about these prob-lems? Well, many people think that electric cars may be the answer. Several carcompanies and research groups have been experimenting with designs for clean,

reliable electric automobiles for several years. Who knows, maybesomeday you’ll drive a car that you plug in instead of filling up!

Clean Driving1. Using the library and the Internet, research elec-tric cars. When was the first electric car built? Howmany different electric car designs can you find?What technological advances have made electric

cars more realistic? How far and how fast can elec-tric cars go? Are there any electric cars on the market

today? How is the electricity for these cars generated?Does this cause pollution? Give an oral presentation to

the class, and include visual aids.

Long-Term Project Ideas2. Electricity from a salt pond? In Israel, test sites at the Dead

Sea have used a salt pond to generate small amounts ofelectricity. The pond acts as a solar collector. Solar pondshave been built around the world. Research how theywork and what locations make a good solar pond. Build a model of a solar salt pond, and design an experiment that tests whether it is a better solar collector than a similar body of fresh water.

3. You can’t always wire something the way you want.Research the local building codes for electrical wiring.Begin by calling the city or village hall and asking whichdepartment is responsible for inspecting electrical wiring.Or, interview a building inspector about the local codes forelectrical wiring. Create a brochure explaining the impor-tance of building codes to new home owners.

4. You’ve been told that you are not supposed to use electri-cal equipment near water. Do you know why? Researchthe safety precautions that you should take when usingelectrical equipment and the science behind those precau-tions. Create a pamphlet of safety precautions peopleshould follow when handling electric equipment.

Name ___________________________________________________ Date _________________ Class _____________

PROJECT

STUDENT WORKSHEET67

The Future Is Electric

INTERNETKEYWORD

solar salt pond

TEACHER-LED DEMONSTRATION

DEMO

57

Purpose

Students observe how the repulsion of likecharges causes a Mylar™ hoop to hoverover an aluminum pie pan.

Time Required

10–15 minutes

Advance Preparation

Mylar foil can be obtained from a first-aidkit or from most arts and crafts stores. Cutthe foil to the proper size. When doing so,be sure the strip has a consistent widthand a mass of 0.03 g or less. Any cornersor jagged edges can disrupt the experi-ment. Join the two ends of the Mylar foilwith rubber cement to form a closed loop.Glue the plastic-foam cup upside down onthe inside of the aluminum pie pan, asshown in the sketch on this page.

What to Do

1. Place the plastic-foam plate upsidedown on a table. Rub the plate with apiece of wool for about a minute. Thiswill negatively charge the plate as elec-trons flow from the wool to the plate.

2. Place the aluminum pie pan upright onthe plastic-foam plate. The negativelycharged plastic-foam plate will attractpositive charges to the bottom of thealuminum pie pan. The top of the alu-minum pie pan will therefore have anegative charge.

3. Briefly touch the top of the pie panwith your finger. Negative charge willflow from the pie pan through your fin-ger to the ground, leaving the pie panwith a positive charge.

4. Lift the pie pan by grabbing the plastic-foam cup. Turn the pan upright and setthe cup on the table. The pan is nowready for the demonstration.

continued...

Hoop It Up

MATERIALS

• piece of Mylar™ foil, at least 0.7 x 35 cm• scissors• rubber cement• plastic-foam cup• aluminum pie pan• small piece of wool• plastic-foam plate

Styrofoam cup

Plastic-foam plate

Aluminum pie pan

TEACHER PREP

CONCEPT LEVEL

CLEAN UP

E A S Y H A R D

Lab Ratings

Alyson MikeRadley Middle SchoolEast Helena, Montana

Copyright © by Holt, Rinehart and Winston. All rights reserved.Copyright © by Holt, Rinehart and Winston. All rights reserved.


Name Class Date

Reaction to StressQuick Lab DATASHEET FOR QUICK LAB

BackgroundThe graph below illustrates changes that occur in the membrane potential of aneuron during an action potential. Use the graph to answer the followingquestions. Refer to Figure 3 as needed.

Analysis1. Determine about how long an action potential lasts.

2. State whether voltage-gated sodium, chanels are open or closed at point A.

3. State whether voltage-gated potassium channels are open or closed atpoint B.

4. Critical Thinking Recognizing Relationships What causes the menberneotential to become less negative at point A?

5. Critical Thinking Recognizing Relationships What causes the membranepotential to become more negative at point B?


Answer here.

Answer here.

Answer here.

Answer here.

Answer here.

Using Scientific Methods

CALCULATOR-BASED LABS 15

Cop

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▼▼▼

“Juice” is a slang term sometimes used to describe electricity. Batteries, which can beused to supply electricity, are made up of one or more cells. Cells consist of two dif-ferent materials (the electrodes) in a solution (the electrolyte) and are connected toeach other by a wire. In this experiment, you will study some basic principles of cellsusing lemon juice as the cell solution. You will use different materials as electrodes inthe lemon cell and use a calculator to measure and display the voltages produced.

Procedure

1. Use a pen to make two parallel marks 1 cm long and 2 cm apart on a lemon. Use a scalpel to cut two slits in thelemon peel at the marks.

Caution: Be very careful not to cut yourself with the scalpel.

2. Attach the red voltage probe lead to one alligator clip andthe black lead to a second alligator clip as shown in theillustration. You will be attaching the alligator clips to thetest materials during this experiment in order to preventcorrosion of the voltage probe leads.

3. Plug the voltage probe into channel 1 (CH 1) of the LabPro or CBL 2 interface. Use the link cable to connectthe TI graphing calculator to the interface. Firmly press inthe cable ends.

4. Turn on the calculator, and start the DataMate program.Press to reset the program.

5. As shown in the illustration below, insert a pencil sharp-ened at both ends, into one of the slits, and insert a nailinto the other slit. Hook the alligator clip attached to thered probe lead to the pencil. Hook the alligator clipattached to the black probe lead to the nail.

Collect Data

6. Observe whether the voltage reading stays constant, rises,or drops. Record your observations in the data table on thenext page.

STUDENT WORKSHEET4

Lemon “Juice”

LAB

Name _______________________________________________ Date ________________ Class______________

MATERIALS

• LabPro or CBL 2 interface

• TI graphing calculator• DataMate program• Vernier voltage probe• 2 alligator clips• lemon• scalpel• graphite pencil (C)• iron nail (Fe)• magnesium strip (Mg)• zinc strip (Zn)• paper towels• pen• metric ruler

alligator clip

graphite pencil

iron nail

red voltage probe

alligator clip black voltage probe

GENERAL

GENERAL

GENERALGENERAL

GENERAL

GENERAL

GENERAL

GENERAL

SPECIAL NEEDS

SPECIAL NEEDS GENERAL

GENERAL

SAMPLE

SAMPLE SAMPLE

SAMPLE SAMPLE

SAMPLE

SAMPLE

SAMPLE

SAMPLESAMPLE

SAMPLE

SAMPLE

SAMPLE

SAMPLE

SAMPLE

SAMPLE

DATASHEETS FORCHAPTER LABS

Teacher’s NotesTIME REQUIRED

One 45-minute class period.

RATINGTeacher Prep–3Student Set-Up–2Concept Level–2Clean Up–2

MATERIALS

The materials listed on the student page are enough for a group of 4–5 students.Large, dried beans of any kind will work well in this exercise.

SAFETY CAUTION

Remind students to review all safety cautions and icons before beginning this labactivity.

Using Scientific MethodsSkills Practice Lab DATASHEET FOR CHAPTER LAB


1 2 3 4Easy Hard

Jason MarshMontevideo High

and Country School

SAMPLE

DATASHEETS FORLABBOOK

Teacher’s NotesTIME REQUIRED

One 45-minute class period.

Does It All Add Up?Skills Practice Lab DATASHEET FOR LABBOOK LAB


Jason MarshMontevideo High

SAMPLE

Is That a Fact!

Is That a Fact!

Copper wireBurner

Iron wire

Ice water

Currentmeter

Chapter Enrichment

This Chapter Enrichment provides relevant and

interesting information to expand and enhance

your presentation of the chapter material.

Electric Charge and Static ElectricityElectroscopes• Although now out-of-date,

the electroscope provideda simple method for mea-suring the amount of elec-tric charge in an object.The distance between thetwo metal leaves (conduc-tors) of an electroscopeindicates the amount ofcharge being conducted.

• The British physicist and chemist Michael Faraday(1791–1867) was the first to detect electric charge byusing an electroscope. He made this observation in theearly 1800s while he was a professor at England’s RoyalInstitution.

◆ To say that something is “charged” is not entirelyaccurate. Objects that we call charged actually have acharge imbalance; they have an unequal number ofprotons and electrons.

Photocopiers and Electric Charge• One use of electric charges is the production of photo-

copied images. The ink on photocopies is made of tinyblack particles. Some photocopiers give these particlesa negative charge. When you put a document in thecopier, it makes a positively charged image of the doc-ument on a rotating drum or belt. The negativelycharged toner particles stick to thepositively charged image. Thenthe machine runs a chargedsheet of paper alongside thedrum, and the particlesmove to the paper. Finally,the machine thermally fusesthe particles to the paper, andthe copy is finished.

Electric Current and Electrical EnergyCells• Cells can be classified into two broad categories:

primary cells and secondary cells. Primary cellsinclude the alkaline dry cell, the acidic dry cell, andthe mercury cell. Secondary cells include the lead-acidbattery, the nickel-iron cell, and the nickel-cadmiumcell. Primary cells cannot be recharged, but secondarycells can be recharged.

Thermoelectricity and Thermocouples• In 1821, a German physicist named Thomas Seebeck

(1770–1831) observed that electrical energy wasgenerated when the ends of two different kinds ofwires were joined and maintained at two differenttemperatures. A thermocouple uses this effect tomeasure temperature differences.

◆ Thermocouple wires are usually made of copper andiron. However, other pairs of metals, such as iron andconstantan (a copper-nickel alloy) and copper andconstantan, are also used.

Alternative Energy Sources• Traditional methods of generating electrical energy

have used fossil fuels, such as coal, as energy sources.But generating energy by burning fossil fuels releasescarbon dioxide gas. Many scientists think that risinglevels of atmospheric carbon dioxide are warming theEarth. This warming could have unwanted effects.Alternatives to fossil fuels exist, including nuclearenergy, solar energy, wind energy, hydroelectric energy(energy from moving water), and geothermal energy(thermal energy from the Earth’s interior).

471E Chapter 17 • Introduction to Electricity

17

Is That a Fact!

Is That a Fact!

100 w120V

LO

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E

120WLONG LIFE130 VOLT

USAZ

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Superconductors• Superconductors are materials that allow electric

charges to flow with no resistance. In 1911, a Dutch physicist named Heike Kamerlingh Onnes (1853–1926) discovered superconductivity. He found that mercury chilled to very low temperatures (below �269°C) offered no electrical resistance.

◆ Initially, liquid helium was used as a coolant for superconductors. But liquefying helium was both expensive and inefficient, making it impractical for widespread use. In the 1980s, researchers found new types of superconductors that worked at higher tem-peratures. So, liquid nitrogen, which is relatively inex-pensive, could be used instead of liquid helium.

Superconducting Magnets• Superconducting magnets generate magnetic fields

with almost no energy loss from resistance. These magnets are used in advanced technological devices, such as particle accelerators and magnetic resonance imaging (MRI) devices.

Electrical CalculationsMeasuring Electricity• An ohm (Ω) is a unit for expressing resistance. For a

given voltage across the device, the lower the resis-tance is, the higher the current in the device.

• An ampere (A) is a unit for expressing current. The more amps there are, the more charges pass the point each second.

• A watt (W) is a unit for expressing power. Electric power is the product of the voltage across a device and the current in the device. Electrical energy can be

converted into other forms of energy and used to do work. Watts are used to express the rate at which the energy is converted.

Electric CircuitsHousehold Circuits• The blueprint of a house includes symbols that indi-

cate where electric wiring belongs, where switches are located, and where light fixtures will be installed. Electricians follow the symbols in the blueprint as they help build the house.

• Closed circuits carry a continuous flow of charges. Open circuits do not carry a flow of charges. Short cir-cuits are closed circuits in which a direct connection is made between terminals, bypassing the loads that pro-vide resistance in the circuit.

◆ A typical water heater uses 4,800 kWh of electrical energy per year. By contrast, an electric toothbrush uses only 5 kWh of electrical energy per year.

SciLinks is maintained by the National Science Teachers Association to provide you and your students with interesting, up-to-date links that will enrich your classroom presentation of the chapter.


Topic: Static ElectricitySciLinks code: HSM1451

Topic: Electric CurrentSciLinks code: HSM0472

Topic: Electrical SafetySciLinks code: HSM0476

Topic: Electrical EnergySciLinks code: HSM0475

Topic: Electric CircuitsSciLinks code: HSM0471

Topic: BatteriesSciLinks code: HSM0139

Visit www.scilinks.org and enter the SciLinks code for more information about the topic listed.

For background information about teaching strategies and

issues, refer to the Professional Reference for Teachers.

OverviewStudents will learn about howobjects become charged andhow charged objects interact.They will also learn about therelationship between electriccurrent, voltage, and resistance.Students will examine someways of generating electricalenergy and how to calculatepower and energy usage. Finally,students will learn about seriesand parallel circuits and electri-cal safety.

Assessing PriorKnowledgeStudents should be familiarwith the following topics:

• atoms

• electrons

• formation of ions

IdentifyingMisconceptionsStudents may think that atomsbecome charged by losing orgaining protons rather than bylosing or gaining electrons.When studying circuits, studentsmight think that a closed switchprevents the flow of charge in acircuit, similar to how a closeddoor prevents the movement ofpeople into a room.

National Science Education Standards

The following codes indicate the National Science EducationStandards that correlate to this chapter. The full text of thestandards is at the front of the book.

Chapter OpenerUCP 5; SAI 1, 2

Section 1 Electric Charge and StaticElectricityUCP 2; SPSP 3, 5; HNS 3; PS 3a; LabBook: UCP 2; SAI 1, 2;PS 3a, 3d

Section 2 Electric Current and ElectricalEnergySPSP 5; PS 3a; LabBook: UCP 2; SAI 1, 2; PS 3a

Section 3 Electrical CalculationsHNS 3; PS 3a

Section 4 Electric CircuitsSPSP 5; PS 3d

Chapter LabUCP 2; SAI 1, 2; PS 3a, 3d

Standards Correlations

17

472 Chapter 17 • Introduction to Electricity

PRE-READINGPRE-READING

Introduction to Electricity

About the

This incredible light display is not an indoorlightning storm, but it’s close! When scientistsat the Sandia National Laboratory fi re thisfusion device, a huge number of electronsmove across the room and make giant sparks.

Layered Book Beforeyou read the chapter,create the FoldNote entitled

“Layered Book” described in the StudySkills section of the Appendix. Label thetabs of the layered book with “Charge,”“Current,” “Voltage,” and “Resistance.” Asyou read the chapter, write informationyou learn about eachcategory under theappropriate tab.

SECTION

Electrical energy is theenergy of electric charges.

17

1 Electric Chargeand Static Electricity . . . . . . . . 474

2 Electric Current andElectrical Energy. . . . . . . . . . . . 482

3 Electrical Calculations . . . . . . . 490

4 Electric Circuits . . . . . . . . . . . . 494

START-UPStick TogetherIn this activity, you will see how a pair of electrically charged objects interact.

Procedure1. Take two strips of cellophane tape. Each strip

should be 20 cm long. Fold over a small part of the end of each strip to form a tab.

2. Hold each piece of tape by its tab. Bring the two pieces of tape close together, but do not let them touch. Record your observations.

3. Tape one of the strips to your lab table. Tape the second strip on top of the first strip.

4. Pull the strips of tape off the table together.

5. Quickly pull the strips apart. Bring the two pieces of tape close together, but do not let them touch. Record your observations.

Analysis1. Compare how the pieces of tape behaved when

you first brought them together with how they behaved after you pulled the pieces apart.

2. As you pulled the pieces of tape apart, electrons from one piece of tape moved onto the other piece of tape. Describe the charge on each piece of tape after you pulled the two pieces apart.

3. From your observations, draw a conclusion about how objects having the charges that you described behave toward one another.

START-UPSTART-UP vvM A T E R I A L S

FOR EACH STUDENT• tape, cellophane, 20 cm (2)

Teacher’s Notes: This activity works best in warm, humid weather. If this activity is done on a cool, dry day, the pieces of tape might be charged when they are first pulled off of the roll and will repel each other at the start.

Answers

1. Sample answer: When the pieces of tape were first brought together, they did not attract or repel. After they were pulled apart and brought back together, the pieces of tape attracted one another.

2. The piece of tape that gained electrons has a negative charge. The piece of tape that lost elec-trons has a positive charge.

3. An object that has a positive charge and an object that has a negative charge attract one another.

Chapter ReviewPS 3a, 3d

Science in ActionSPSP 5; HNS 1

nt ro c t ion o f l e c t r ic i t

The most shocking of all fish tales concerns the electric eel, a freshwater fish ofCentral America and outh America thatcan produce powerful jolts of electricalenergy. Electric discharges from this 2. mlong creature are strong enough to stunand kill smaller fish and frogs in the water.The eel can then swallow its motionlessprey whole. Early travelers to the AmaonRiver basin wrote that, in shallow pools,the eels electric discharges could knockhorses and humans over.

How does the electric eel perform itsshock ing feat ithin this fishs long bodyare a series of electroplatesmodifiedmuscle tissues that generate low voltages.The electricity produced by one waferthinelectroplate is small. But eels have ,000to ,000 electroplates connected togetherand can therefore produce a high voltage.In laboratory eperiments, the bursts ofvoltage from a fully grown eel have beenmeasured at around 00 volts. Thats five

times the voltage of an electrical outletall from the cells of a single fish The eelsthick, leathery skin prevents the eel fromelectrocuting itself while apping prey.

ow that you know what one amaingfish can do with electricity, read on tolearn what people have accomplishedwith this versatile form of energy.

Copyright ' by Holt, Rinehart and Winston. All rights reserved.

Strange but True!

Chapter Starter TransparencyUse this transparency to help students begin thinking about electricity.

CHAPTER RESOURCESTechnology

Transparencies • Chapter Starter Transparency

Student Edition on CD-ROM

Guided Reading Audio CD • English or Spanish

Classroom Videos • Brain Food Video Quiz

Workbooks

Science Puzzlers, Twisters & Teasers • Introduction to Electricity g

READINGSKILLS

Chapter 17 • Introduction to Electricity 473

READING STRATEGY

Nucleus

Electron

Proton

Neutron

Electric Charge and Static ElectricityHave you ever reached out to open a door and received a shock from the doorknob? Why did that happen?

On dry days, you might get a shock when you open a door,put on a sweater, or touch another person. These shocks comefrom static electricity. To understand static electricity, you needto learn about atoms and charge.

Electric ChargeAll matter is made up of very small particles called atoms.Atoms are made of even smaller particles called protons, neu-trons, and electrons, which are shown in Figure 1. How dothese particles differ? For one thing, protons and electrons arecharged particles, and neutrons are not.

✓✓Reading Check What are the two types of charged particles in atoms? (See the Appendix for answers to Reading Checks.)

Charges Exert ForcesCharge is a physical property. An object can have a positivecharge, a negative charge, or no charge. Charge is best under-stood by learning how charged objects interact. Charged objectsexert a force—a push or a pull—on other charged objects. Thelaw of electric chargeslaw of electric charges states that like charges repel, or push away,and opposite charges attract. Figure 2 illustrates this law.

Figure 1 Protons and neutrons make up the center of the atom, the nucleus. Electrons are found outside the nucleus.

1What You Will Learn

Describe how charged objectsinteract by using the law of electriccharges.Describe three ways in which anobject can become charged.Compare conductors with insulators.Give two examples of static electricityand electric discharge.

Vocabularylaw of electric chargeselectric forceelectric fieldelectrical conductorelectrical insulatorstatic electricityelectric discharge

Reading Organizer As you readthis section, create an outline of thesection. Use the headings from thesection in your outline.

OverviewThis section explains whatelectric charge is and how itworks and explains the threeways that objects can becomecharged. Students learn aboutconductors and insulators.Finally, the section discussesstatic electricity and electricdischarge.

BellringerWrite the term electric charge onthe board. Ask students to writea definition for this term intheir own words.

vv---------------------------------------------------g

Balloons and StaticElectricity Distribute twoinflated balloons and a piece ofwool cloth to pairs of students.Instruct students to create staticelectricity by rubbing their bal-loons against the cloth. Askthem to describe what theyobserve when they hold the bal-loons close to their hair. (Theirhair will move toward the balloon.)

Tell students that static electric-ity, which will be explained inthis section, is responsible fortheir observation. l Kinesthetic

Answer to Reading Check

protons and electrons

1

Is That a Fact!The word electricity is derived fromelektron, the Greek word for amber(fossilized tree sap). Thales, a Greek phi-losopher, observed that bits of strawwere attracted to amber after the amberwas rubbed with cloth.

CHAPTER RESOURCES

Chapter Resource File

CRF • Lesson Plan • Directed Reading Ab • Directed Reading Bs

Technology

Transparencies• Bellringer• P67 Structure of an Atom• P68 Law of Electric Charges

Workbooks

Interactive Textbook Struggling Readers Struggling Readers


The Force Between Protons and Electrons

Protons are positively charged. Electrons are negatively charged.

Because protons and electrons have opposite charges, they are

attracted to each other. Without this attraction, electrons could

not be held in atoms.

The Electric Force and the Electric Field

The force between charged objects is an electric force. The size

of the electric force depends on two things. The first thing is

the amount of charge on each object. The greater the charge

is, the greater the electric force is. The other thing that deter-

mines the size of the electric force is the distance between the

charges. The closer together the charges are, the greater the

electric force is.

Charged things are affected by electric force because charged

things have an electric field around them. An electric field is

the region around a charged object in which an electric force

is exerted on another charged object. A charged object in the

electric field of another charged object is attracted or repelled

by the electric force acting on it.

Objects that have thesame charge repel eachother. Each object exertsa force on the otherobject. These forces pushthe objects apart.

Objects that have oppositecharges are attracted to eachother. Each object exerts aforce on the other object. Theseforces pull the objects together.

The Law of Electric ChargesFigure 2

law of electric charges the lawthat states that like charges repeland opposite charges attract

electric force the force of attrac-tion or repulsion on a chargedparticle that is due to an electric field

electric field the space arounda charged object in which anothercharged object experiences anelectric force

vv--------------------------------------------------------b

Exploring ChargeM A T E R I A L S

FOR EACH PAIR• balloon (2)• cloth, wool or silk• string, 1 m (2)

1. Have students inflate theballoons and tie a 1 m lengthof string to each one.

2. Tell one member of each pairto grasp one string in eachhand about 0.5 m down thestring from the balloons.

3. Instruct the other member torub one of the balloons withthe cloth about 10 times.

4. Release the rubbed balloon,and allow it to hang freelynext to the other balloon.

5. Ask students to share theirobservations. (The balloonsmove toward each other.)

6. Next, have students rub bothballoons with the cloth andobserve what happens. (Theballoons, which now have thesame charge, move away fromeach other.)

7. Have students record theirobservations.

l Visual/Kinesthetic

CONNECTION toCONNECTION toHistory --------------------------------------------------g

Statesman and Scientist BenjaminFranklin (1706–1790) is an important fig-ure in the history of the United States. Hesigned the Declaration of Independenceand the Constitution (both of which hehelped write), and he was integral to the

development of our postal system. Franklinalso made important contributions to sci-ence, including the study of electricity. Forexample, he introduced the terms positiveand negative as they relate to electriccharge, and he invented the lightning rod.

Section 1 • Electric Charge and Static Electricity 475

Charge It!Atoms have equal numbers of protons and electrons. Becausean atom’s positive and negative charges cancel each other out,atoms do not have a charge. So, how can anything made ofatoms be charged? An object becomes positively charged whenit loses electrons. An object becomes negatively charged whenit gains electrons. Objects can become charged by friction,conduction, and induction, as shown in Figure 3.

✓Reading Check What are three ways of charging an object?

FrictionCharging by friction happens when electrons are “wiped” fromone object onto another. If you use a cloth to rub a plasticruler, electrons move from the cloth to the ruler. The ruler gainselectrons and becomes negatively charged. At the same time,the cloth loses electrons and becomes positively charged.

ConductionCharging by conduction happens when electrons move fromone object to another by direct contact. Suppose you touchan uncharged piece of metal with a positively charged glassrod. Electrons from the metal will move to the glass rod. Themetal loses electrons and becomes positively charged.

Movementof electrons

The friction of rubbing aballoon on your hair causeselectrons to move fromyour hair to the balloon.Your hair and the balloonbecome oppositely chargedand attract each other.

Friction Conduction Induction

When a negatively chargedplastic ruler touches anuncharged metal rod,the electrons in the rulertravel to the rod. Therod becomes negativelycharged by conduction.

A negatively charged balloonmakes a small section of ametal beam have a positivecharge through induction.Electrons in the metal arerepelled by and move awayfrom the balloon.

Three Ways to Charge an ObjectFigure 3

SKILLPainting CarsResearch how

charge and electric force areused by car makers to paintcars. Then, in your sciencejournal, write a one-pagereport describing the processand explaining how the useof charge to paint cars helpsprotect the environment.

READINGSTRATEGY -------------------------b

Prediction Guide Before stu-dents read the passage aboutfriction, conduction, and induc-tion, ask them to explain whatthey think these terms meanand to think of an example ofeach term. Then, have themevaluate their responses afterreading these pages. l Logical


friction, conduction, and inductionMISCONCEPTION

ALERT

Gain or Lose Only Electrons Studentsmay think that atoms can gain or loseprotons as well as electrons. Remindstudents that atoms can lose or gainonly electrons, which are negativelycharged. A net loss of electrons leavesan atom positively charged, whereas anet gain of electrons leaves an atomnegatively charged.

SUPPORT FOR

English LanguageLearnersFriction, Conduction, andInduction A demonstrationwill help students compre-hend the concepts of friction,conduction, and induction.After they have read the text,write the terms on the board.Model pronunciation, andhave students repeat. Then,demonstrate examples, nar-rating as you do so. Use thesematerials:• For friction, an inflated

balloon (Rub the balloon toshow static electricity.)

• For conduction, a glassstirring rod, a metal skewer,a bowl of rice cereal (Placethe skewer in the cereal; rubthe glass rod with cloth tocreate a static charge; touchthe rod to the skewer.)

• For induction, an inflatedballoon (Rub the balloonagainst cloth, and placenear a metal object.)

As you finish each demonstra-tion, ask students to name themethod of charging aloud.l Visual


InductionCharging by induction happens when charges in an uncharged metal object are rearranged without direct contact with a charged object. Suppose you hold a metal object near a positively charged object. The electrons in the metal are attracted to and move toward the positively charged object. This movement causes (or induces) an area of negative charge on the surface of the metal.

Conservation of ChargeWhen you charge something by any method, no charges are created or destroyed. The numbers of electrons and protons stay the same. Electrons simply move from one atom to another, which makes areas that have different charges. Because charges are not created or destroyed, charge is said to be conserved.

Detecting ChargeYou can use a device called an electroscope to see if something is charged. An electroscope is a glass flask that has a metal rod in its rubber stopper. Two metal leaves are attached to the bottom of the rod. When the electroscope is not charged, the leaves hang straight down. When the electroscope is charged, the leaves repel each other, or spread apart.

Figure 4 shows a negatively charged ruler touching the rod of an electroscope. Electrons move from the ruler to the electroscope. The leaves become negatively charged and repel each other. If something that is positively charged touches the neutral rod, electrons move off the electroscope. Then, the leaves become positively charged and repel each other. An electroscope can show that an object is charged. However, it cannot show whether the charge is positive or negative.

✓Reading Check What can you do with an electroscope?

Figure 4 When an electro-scope is charged, the metal leaves have the same charge and repel each other.

Detecting Charge1. Use scissors to cut two strips of aluminum

foil that are 1 cm � 4 cm each.2. Bend a paper clip to make a hook. (The clip

will look like an upside-down question mark.)3. Push the end of the hook through the middle

of an index card, and tape the hook so that it hangs straight down from the card.

4. Lay the two foil strips on top of one another, and hang them on the hook by gently pushing the hook through them.

5. Lay the card over the top of a glass jar.6. Bring various charged objects near the top of

the paper-clip hook, and observe what happens. Explain your observations.


vv------------------------------------------b

Electron Transfer Do the fol-lowing demonstration to help students visualize the transfer of electrons between objects. Hold up a chalk eraser saturated with dust. Tell the class that the eraser represents a negatively charged object, the chalk particles repre-sent electrons, and the (clean) board represents an uncharged object. Wipe the board with the eraser. Students will observe the “electron trail” that the chalk leaves behind. l Visual ee

M A T E R I A L SFOR EACH GROUP

• aluminum foil (2 pieces)• index card• jar, glass, medium-sized• objects that can be charged (balloons; rubber, plastic, and glass rods; plastic ruler; wool and silk cloth)• paper clip• scissors

Safety Caution: Remind students to review all safety cautions and icons before beginning this activity.

Teacher’s Note: Some stu-dents will touch the paper clip with a charged object. Others will hold a charged object near the paper clip. These two methods give you a chance to discuss the differ-ence between charging by conduction and charging by induction.

Answer

6. Students should observe that the two leaves of foil in the jar spread apart when a charged object is brought near or touched to the paper clip.


You can use an electroscope to detect whether an object is charged.

A Van de Graaff generator is a machine that continuously produces a charge on its domed metal surface. If you have your hands on the dome, electrons will transfer between you and the dome by conduction, causing your hair to stand on end! Your hair becomes charged, and the like-charged strands of hair repel each other.

electrical conductor a material in which charges can move freely

electrical insulator a material in which charges cannot move freely

static electricity electric charge at rest; generally produced by fric-tion or induction

Moving ChargesLook at Figure 5. Have you ever noticed that electrical cords are often made from metal and plastic? Different mate-rials are used because electric charges move through some materials more easily than they move through others. Most materials are either conductors or insulators based on how easily charges move in them.

ConductorsAn electrical conductor is a material in which charges can move easily. Most metals are good conductors because some of their electrons are free to move. Conductors are used to make wires. For example, a lamp cord has metal wire and metal prongs. Copper, aluminum, and mercury are good conductors.

InsulatorsAn electrical insulator is a material in which charges cannot move easily. Insulators do not conduct charges very well because their electrons cannot flow freely. The electrons are tightly held in the atoms of the insulator. The insulating material in a lamp cord stops charges from leaving the wire and protects you from electric shock. Plastic, rubber, glass, wood, and air are good insulators.

Static ElectricityAfter you take your clothes out of the dryer, they sometimes are stuck together. They stick together because of static electricity. Static electricity is the electric charge at rest on an object.

When something is static, it is not moving. The charges of static electricity do not move away from the object that they are in. So, the object keeps its charge. Your clothes are charged by friction as they rub against each other inside a dryer. As the clothes tumble, negative charges are lost by some clothes and build up on other clothes. When the dryer stops, the transfer of charges also stops. And because clothing is an insulator, the built-up electric charges stay on each piece of clothing. The result of this buildup of charges is static cling.

Figure 5 These jumper cables are made of metal, which carries electric charges, and plastic, which keeps the charges away from your hands.


Discussion -----------------------------------gCharge and Insulation Lead students in a discussion about the role of insulation in main-taining an object in a charged state. Explain that a conductor must be insulated from other conductors in order to be charged. Otherwise, electrons will flow from one conductor to the next.

Ask students why the metal rod in an electroscope is able to hold a charge. (because it is insulated by the rubber stopper)

Then, ask what would happen if someone touched the metal rod. (It would become uncharged as electrons flowed between the rod and the person.) l Logical

h ----------------------------g

Writing Static Cling Tell stu-dents to observe the effect of static electricity

in the clothes dryer at home. Instruct them to put a few damp clothes (a combination of fiber types works best) into the dryer with no fabric softener. When the clothes have dried, students should observe a static charge as they separate the clothes. Then, tell students to put the clothes back in the dryer, this time with a fabric-softener sheet. Have them research how fabric soft-ener reduces static electricity and report their findings in a brief report. l Interpersonal

Static Charge and Humidity Students may have observed that static electricity is more noticeable when the air is dry. Ask students to think about why the amount of moisture in the air would affect static electricity. Explain that moisture in the air coats objects and reduces their resistance, so charge is more quickly neutralized when the air is humid than when it is dry.

Electric DischargeCharges that build up as static electricity on an object even-tually leave the object. The loss of static electricity as chargesmove off an object is called electric discharge. Sometimes,electric discharge happens slowly. For example, clothes stucktogether by static electricity will eventually separate on theirown. Over time, their electric charges move to water moleculesin the air.

Sometimes, electric discharge happens quickly. It may hap-pen with a flash of light, a shock, or a crackling noise. Forexample, when you wear rubber-soled shoes and walk on carpet,negative charges build up on your body. When you reach outfor a metal doorknob, the negative charges on your body canjump to the doorknob. The electric discharge happens quickly,and you feel a small shock.

One of the most dramatic examples of electric dischargeis lightning. How does lightning form through a buildup ofstatic electricity? Figure 6 shows the answer.

✓Reading Check What is electric discharge?

electric discharge the release ofelectricity stored in a source

The negative charge at the bottom of thecloud may induce a positive charge on theground. The large charge difference causesa rapid electric discharge called lightning.

b

How Lightning FormsFigure 6

During a thunderstorm, water drop-lets, ice, and air move inside thestorm cloud. As a result, negativecharges build up, often at thebottom of the cloud. Positivecharges often build up at the top.

a

Different parts of cloudshave different charges. Infact, most lightning happenswithin and between clouds.

c

Research -------------------------------------------a

PORTFOLIO

Types of LightningLightning comes in sev-

eral different shapes and forms.Ball, forked, sheet, and beadlightning are a few examples.Have students research themany forms of lightning.Encourage them to be creativein the presentation of theirresults. Ask them to includephotographs, if possible.l Logical

Struck by Lightning Theelectric discharge from a sin-gle stroke of lightning iscaused by a voltage buildupof 10 million to 100 millionvolts between a cloud andthe Earth. In July 1997, at amusic festival in Haverhill,England, 45 people weresimultaneously struck bylightning. To everyone’s sur-prise, no one was killed orbadly injured.

Going Further -------------------gWriting Franklin’s Kite Have

students researchBenjamin Franklin’s

famous kite-flying experiment.Different sources may give dif-ferent accounts of the incident.Encourage students to writetheir findings as a report or tomake a model or a poster, and toshare it with the class. l Verbal


Electric discharge is the release ofelectricity stored in a source.

CHAPTER RESOURCESTechnology

Transparencies• P69 How Lightning Forms

CulturalAwarenessCulturalAwareness g

The Meaning of Lightning Differentcultures have ascribed different mean-ings to lightning. In some Africancultures, people struck by lightningwere considered cursed.


Lightning DangersLightning usually strikes the highest point in a charged area because that point provides the shortest path for the charges to reach the ground. Anything that sticks up or out in an area can provide a path for lightning. Trees and people in open areas are at risk of being struck by lightning. For this reason, it is particularly dangerous to be at the beach or on a golf course during a lightning storm. Even standing under a tree during a storm is dangerous. The charges from lightning striking a tree can jump to your body.

✓Reading Check Why is it dangerous to be outside in an open area during a storm?

Lightning RodsA lightning rod is a pointed rod connected to the ground by a wire. Lightning rods are often mounted so that they are the tallest point on a building, as shown in Figure 7. Objects, such as a lightning rod, that are joined to Earth by a conduc-tor, such as a wire, are grounded. Any object that is grounded provides a path for electric charges to move to Earth. Because Earth is so large, it can give up or absorb charges without being damaged. When lightning strikes a lightning rod, the electric charges are carried safely to Earth through the rod’s wire. By directing the charge to Earth, the rods prevent lightning from damaging buildings.

Figure 7 Lightning strikes the lightning rod rather than the building, because the lightning rod is the tallest point on the building.

Benjamin Franklin In addition to being a states-man, Benjamin Franklin was a scientist. Research Franklin’s discovery that lightning is a form of electricity. Make a poster describing the proce-dures that he used, the terms that he coined, and the inven-tions related to electricity that he designed.


Reteaching -------------------------------------bFiguring Out the Charge Help students who are having diffi-culty by using a rough analogy to relate the charge on an object to feelings. Have students describe how they would feel if they received bad news. This represents gaining negatively charged electrons. Then, have students describe how they would feel if they talked with a friend who was able to relieve some of the bad feelings. This represents losing electrons. l Intrapersonal/Logical

Quiz ---------------------------------------------------------------------g

Ask students to answer the following items:

1. Briefly explain the relation-ship between charge and force. (Charge is a physical prop-erty. Objects with a positive or negative charge exert a force on other charged objects.)

2. Discuss the difference between an electrical conductor and an electrical insulator. Give an example of each. (Chargesmove easily in an electrical con-ductor but have difficulty moving in an electrical insulator. Most metals are conductors. Plastic, rubber, and glass are insulators.)

AlternativeAssessment ---------------------------g

PORTFOLIO

Concept MappingHave students make a

concept map that identifies and briefly explains the three meth-ods of charging. l Visual


Sample answer: A person in an open area might be the tallest object and might provide a path for lightning.

For a variety of links related to this chapter, go to www.scilinks.org

SummarySummary

Review

• The law of electric charges states that like charges repel and opposite charges attract.

• The size of the electric force between two objects depends on the size of the charges exerting the force and the distance between the objects.

• Charged objects exert a force on each other and can cause each other to move.

• Objects become charged when they gain or lose electrons.

• Objects may become charged by friction, conduction, or induction.

• Charges are not created or destroyed and are said to be conserved.

• Charges move easily in conductors but do not move easily in insulators.

• Static electricity is the buildup of electric charges on an object. It is lost through electric discharge.

Using Key Terms

For each pair of terms, explain how the meanings of the terms differ.

1. static electricity and electric discharge

2. electric force and electric field

3. electrical conductor and electrical insulator

Understanding Key Ideas

4. Which of the following is an insulator?a. copperb. rubberc. aluminumd. iron

5. Compare the three methods of charging.

6. What does the law of electric charges say about two objects that are positively charged?

7. Give two examples of static electricity.

8. List two examples of electric discharge.

Critical Thinking

9. Analyzing Processes Imagine that you touch the top of an electroscope with an object. The metal leaves spread apart. Can you determine whether the charge is posi tive or negative? Explain your answer.

10. Applying Concepts Why is it important to touch a charged object to the metal rod of an electroscope and not to the rubber stopper?

Interpreting Graphics

The photograph below shows two charged balloons. Use the photograph below to answer the questions that follow.

11. Do the balloons have the same charge or opposite charges? Explain your answer.

12. How would the photograph look if each balloon were given the charge opposite to the charge it has now? Explain your answer.

Topic: Static ElectricitySciLinks code: HSM1451


4. b5. Charging by friction hap-

pens when charges are trans-ferred from one object to another as they rub together. Charging by conduction hap-pens when charges move between a charged object and a neutral object. Charging by induction happens when the charges in a metal object are rearranged as a result of a nearby charged object.

6. The law of electric charges says that two objects that are positively charged will repel one another.

7. Examples of static electric-ity include static cling and a charged balloon.

8. Examples of electric dis-charge include lightning and the spark when you reach out for a doorknob after walking across a carpet.

9. You cannot tell whether the charge is positive or negative. The leaves of the electroscope will spread apart no matter which charge is present.

10. The metal rod is a conductor, so electrons can easily move down the rod to the metal leaves or up the rod from the metal leaves and confirm any charge present. The rubber stopper is an insulator. Electrons will not move through rubber, so the electroscope will not perform as intended.

11. The balloons have the same charge. Each balloon is pushing the other away.

12. The photograph would look the same. The balloons have the same charge. Giving each bal-loon the opposite charge to the charge it has now would mean that the balloons would still have the same charge and would repel one another.

CHAPTER RESOURCES


CRF • Section Quiz g • Section Review g • Vocabulary and Section Summary g • Reinforcement Worksheet b • Datasheet for Quick Lab

Technology

Interactive Explorations CD-ROM • Tunnel Vision

Answers to Section Review

1. Static electricity is the buildup of electric charges on an object. Electric discharge happens when the electric charges move off of an object.

2. Electric force is the push or pull on a charged object that is a result of an electric field.

3. Electric charges move freely in an electrical conductor. Electric charges do not move freely in an electrical insulator.

READING STRATEGY

Electric Current and Electrical EnergyYou might not realize that when you watch TV, use a computer, or even turn on a light bulb, you depend on moving charges for the electrical energy that you need.

Electrical energy is the energy of electric charges. In most ofthe things that use electrical energy, the electric charges flowthrough wires. As you read on, you will learn more about howthis flow of charges—called electric current—is made and howit is controlled in the things that you use every day.

Electric CurrentAn electric currentelectric current is the rate at which charges pass a givenpoint. The higher the current is, the greater the number ofcharges that pass the point each second. Electric current isexpressed in units called amperes (AM PIRZ), which is oftenshortened to amps. The symbol for ampere is A. And in equa-tions, the symbol for current is the letter I.

✓✓Reading Check What is the unit of measurement for electric current? (See the Appendix for answers to Reading Checks.)

Making Charges MoveWhen you flip the switch on a flashlight, the light comes oninstantly. But do charges in the battery instantly reach the bulb?No, they don’t. When you flip the switch, an electric field isset up in the wire at the speed of light. And the electric fieldcauses the free electrons in the wire to move. The energy ofeach electron is transferred instantly to the next electron, asshown in Figure 1.

2

Figure 1 Electrons moving in a wire make up current and provide energy to the things that you use each day.

What You Will Learn

Describe electric current.Describe voltage and its relationshipto electric current.Describe resistance and itsrelationship to electric current.Explain how a cell generateselectrical energy.Describe how thermocouples andphotocells generate electrical energy.

Vocabularyelectric currentvoltageresistancecellthermocouplephotocell

Reading Organizer As you read thissection, make a table comparing elec-tric current, voltage, and resistance.

OverviewThis section defines current andexplains the two types of cur-rent: AC and DC. Students learnabout voltage and resistance,including factors that affectresistance. Students also learnhow batteries, thermocouples,and photocells generate electri-cal energy from different formsof energy.

BellringerWrite the following questionon the board: “What is thedifference between somethingthat is direct and somethingthat is alternating?” Discussstudent responses.

Discussion ----------------------------------gWhat’s Inside? Show students aphoto or illustration of theinside of a car battery or D cell.Ask them to describe, based onwhat they see, how they thinka battery generates electricalenergy. Tell them that they willlearn the answer in thissection.l Visual ee


amperes (A)

2

Q: What part of the newspaper do

electricians read first?

A: current events

CHAPTER RESOURCES



Technology

Transparencies• Bellringer

Workbooks



ONE WAY

TWO WAY

Direct Current

Alternating Current

electric current the rate at whichcharges pass through a given point;measured in amperes

Figure 2 Charges move inone direction in DC, butcharges continually changedirection in AC.Commanding Electrons to Move

This electric field is created so quickly that all electrons startmoving through the wire at the same instant. Think of theelectric field as a command to the electrons to charge ahead.The light comes on instantly because all of the electrons obeythis command at the same time. So, the current that lightsthe bulb is established very quickly even though each electronmoves quite slowly. In fact, a single electron may take morethan an hour to travel 1 m through a wire.

AC and DCThere are two kinds of electric current—direct current (DC) andalternating current (AC). Look at Figure 2. In direct current,the charges always flow in the same direction. In alternatingcurrent, the charges continually shift from flowing in onedirection to flowing in the reverse direction.

The electric current from the batteries used in a camera isDC. The electric current from outlets in your home is AC. Inthe United States, the alternating current changes directions120 times each second, or has 60 cycles each second.

Both kinds of current can give you electrical energy. Forexample, if you connect a flashlight bulb to a battery, the lightbulb will light. And you can light a household light bulb byputting it in a lamp and turning the lamp on.

✓Reading Check What are two kinds of electric current?

StrategiesStrategiesINCLUSIONINCLUSION

• Learning Disabled• Attention Deficit Disorder• Developmentally DelayedRole-play the differencesbetween AC and DC. Ask stu-dents to line up and marchcompletely around the roomgoing in one direction.Discuss that charges in directcurrent (DC) also goes in onedirection. Ask students toline up again and go in onedirection for the count of fiveand then reverse and go inthe other direction for thecount of five. Tell them youwill call out “Alternate!”when you want them toswitch. After several switches,stop and discuss that thisalternating back and forthis the way that charges inalternating current(AC) move.l Kinesthetic ee


alternating current (AC) and directcurrent (DC)

oTesla and Edison In the late 1800s, a con-troversy brewed between advocates of alter-nating current and advocates of directcurrent. The Croatian-born inventor NikolaTesla and the American inventor ThomasEdison championed their respective inven-tions. Eventually, the advantages of Tesla’sAC system won out, and it was demon-strated to the public at the 1893 World’sColumbian Exposition, in Chicago.

SUPPORT FOR

English LanguageLearnersWord Webs Students willbetter absorb the specializedvocabulary of this section bylinking it to prior knowledge.As they read, have them cre-ate a word web for each of thefollowing terms: alternatingcurrent, direct current, volt-age, amperes, resistance. Tellstudents to write words theyalready know that will helpthem remember the mean-ings of the terms. Evaluate thewebs on the number and ap-propriateness of words used,as well as spelling. Return thewebs to students for correc-tion and to use as referencematerials throughout thechapter.l Verbal/Intrapersonal

Section 2 • Electric Current and Electrical Energy 483

VoltageIf you are on a bike at the top of a hill, you know that you canroll down to the bottom. You can roll down the hill becauseof the difference in height between the two points. The “hill”that causes charges in a circuit to move is voltage. Voltage isthe potential difference between two points in a circuit. It isexpressed in volts (V). In equations, the symbol for voltageis the letter V.

✓Reading Check What is the unit of measurement for voltage?

Voltage and EnergyVoltage is a measure of how much work is needed to move acharge between two points. You can think of voltage as theamount of energy released as a charge moves between twopoints in the path of a current. The higher the voltage is, themore energy is released per charge.

Voltage and Electric CurrentAs long as there is a voltage between two points on a wire,charges will flow in the wire. The size of the current dependson the voltage. The greater the voltage is, the greater thecurrent is. A greater current means that more charges movein the wire each second. A large current is needed to starta car. So, the battery in a car has a fairly high voltage of12 V. Figure 3 shows batteries that have a number of differentvoltages. If you have a device that uses direct current, one ofthese batteries might help.

voltage the potential differ-ence between two points;measured in volts

Figure 3 Batteries are made withvarious voltages for use in manydifferent devices.

12 V

9 V1.5 V

6 V


volts (V)

Research -------------------------------------------aWriting Alternative Energy

Encourage students toresearch and write about

one alternative way of produc-ing electrical energy, such asusing wind or water power. Tellthem to include a basic explana-tion of the scientific principlesinvolved. l Logical

CONNECTION toCONNECTION toHistory --------------------------------------------------g

Count Volta The Italian physicist CountAlessandro Volta (1745–1827) probablydeveloped the first battery in the late1790s. His battery was a stack of pairs ofsilver and zinc disks separated by disks ofcardboard moistened with salt solution.Napoleon bestowed the title of “Count” onVolta for his work on electricity. The volt isnamed after him.


Varying Nature of VoltageThings that run on batteries usually need a low voltage. For example, a portable radio might need only 3 V. Compare the voltage of such a radio with the voltage created by the eel in Figure 4. Most devices in your home use alternating current from an outlet. In the United States, electrical outlets usually supply AC at 120 V. So, most electrical devices, such as televi-sions, toasters, and alarm clocks, are made to run on 120 V.

ResistanceResistance is another factor that determines the amount of current in a wire. Resistance is the opposition to the flow of electric charge. Resistance is expressed in ohms (, the Greek letter omega). In equations, the symbol for resistance is the letter R.

You can think of resistance as “electrical friction.” The higher the resistance of a material is, the lower the current in the material is. So, if the voltage doesn’t change, as resistance goes up, current goes down. An object’s resistance depends on the object’s material, thickness, length, and temperature.

Resistance and MaterialGood conductors, such as copper, have low resistance. Poor conductors, such as iron, have higher resistance. The resistance of insulators is so high that electric charges cannot flow in them. Materials with low resistance, such as copper, are used to make wires. But materials with high resistance are also helpful.For example, the high resistance of the filament in a light bulb causes the light bulb to heat up and give off light.

Figure 4 An electric eel can create a voltage of more than 600 V!

resistance in physical science, the opposition presented to the current by a material or device

Help for a Heart Pacemaker cells in the heart produce low electric currents at regular intervals to make the heart beat. During a heart attack, pacemaker cells do not work together, and the heart beats irregularly. Research how doctors sometimes “jump start” the heart during a heart attack. Make a poster to share your findings.


Discussion ----------------------------------gElectrician Invite a local elec-trician or electrical engineer to visit the classroom to talk about working with and around elec-tric current. Ask your guest to discuss the safety aspects of his or her job. Before the speaker’s visit, ask students to write down one or two questions to ask the speaker. l Interpersonal

READINGSTRATEGY --------------------g

Prediction Guide Before stu-dents read the passage on resis-tance, ask them to choose the correct term in the following statements:

1. If resistance in a material increases and the voltage across the object is constant, current (increases, decreases). (decreases)

2. Assuming constant voltage, the (higher, lower) the resistance is, the higher the current. (lower)

3. Resistance depends on an object’s material, thickness, length, and (color, temperature). (temperature)

l Visual

A span of electrical transmission line between two support structures stretches 5,379 m across the Ameralik Fjord, in Greenland. The line weighs 42 tons!

Resistance, Thickness, and LengthTo understand how the thickness and length of a wire affect the wire’s resistance, look at the model in Figure 5. The pipe filled with gravel represents a wire. The water flowing through the pipe represents electric charges.

Resistance and Temperature Resistance also depends on tempera ture. In general, the resis-tance of metals increases as temperature rises. The atoms vibrate faster at higher temperatures and get in the way of the flowing electric charges. If you cool certain materials to a very low temperature, resistance will drop to 0 . Materials in this state are called superconductors. A small superconductor is shown in Figure 6. Very little energy is wasted when electric charges move in a superconductor. However, a large amount of energy is needed to cool them. Scientists are studying how superconductors can be used to store and transmit energy.

A Model of ResistanceFigure 5

Figure 6 One interesting property of superconductors is that they repel magnets. The superconductor in this photo is repelling the magnet so strongly that the magnet is floating.

A short pipe has less resis-tance than a long pipe does because the water in a short pipe does not have to work its way around as many pieces of gravel.

A thick pipe has less resistance than a thin pipe does because there are more spaces between pieces of gravel in a thick pipe for water to flow through.


GroupGroup vv -------g

Modeling Resistance Divide the class into groups of two or three. Instruct each group to cre-ate a model or a poster that illustrates the factors that affect resistance—material, thickness, length, and temperature. Encourage students to show clearly why a short, thick pipe, for example, has less resistance than a long, narrow one. Give students 2–3 days to complete their project. They can then make a short presentation about their poster or model to the class. l Visual/Verbal cc

MISCONCEPTIONALERT

Wandering Electrons Elec-trons do not travel single file in a straight line through a wire. Instead, electrons move in the wire much like water would move through the spaces in a pipe filled with rocks. Electrons frequently change direction because of interactions with atoms and other electrons.

There was tin being electrically inducted

By current that it naturally conducted.

Then along came some fool,

Who said, “Let’s make tin cool!”

And now the tin’s superconducted!

Flow

Generating Electrical EnergyYou know that energy cannot be created or destroyed. It canonly be changed into other kinds of energy. Many thingschange different kinds of energy into electrical energy. Forexample, generators convert mechanical energy into electricalenergy. Cells change chemical or radiant energy into electricalenergy. Batteries are made of one or more cells.

Parts of a CellA cell, such as the one in Figure 7, contains a mixture ofchemicals called an electrolyte (ee LEK troh LIET). Electrolytesallow charges to flow. Every cell also has a pair of electrodesmade from conducting materials. An electrode (ee LEK TROHD)is the part of a cell through which charges enter or exit.Chemical changes between the electrolyte and the electrodesconvert chemical energy into electrical energy.

Kinds of CellsTwo kinds of cells are wet cells and dry cells. Wet cells, suchas the one in Figure 7, have liquid electrolytes. A car battery ismade of several wet cells that use sulfuric acid as the electrolyte.You can make your own wet cell by poking strips of zinc andcopper into a lemon. When the metal strips are connected,enough electrical energy is generated to run a small clock, asshown in Figure 8. Dry cells work in a similar way. But theelectrolytes in dry cells are solid or pastelike. The cells usedin small radios and flashlights are types of dry cells.

✓Reading Check What are two kinds of cells?

A chemical reaction with theelectrolyte leaves extra elec-trons on one electrode. Thiselectrode is made of zinc.

a

A different chemical reactioncauses electrons to be pulledoff the other electrode. Inthis cell, this electrode ismade of copper.

b

If the electrodes are con-nected by a wire, electronsflow through the wire andions move in the electrolyte.The moving charges makean electric current.

c

How a Cell WorksFigure 7

cell in electricity, a device thatproduces an electric current byconverting chemical or radiantenergy into electrical energy

Figure 8 This cell usesthe juice of a lemon as anelectrolyte and uses strips ofzinc and copper as electrodes.

vv---------------------------------------------------a

Lemon Cells A variation of thelemon clock pictured inFigure 8 can be constructed eas-ily in the classroom. Divide stu-dents into small groups for thisactivity.

M A T E R I A L SFOR EACH GROUP• cables with alligator clips (2)• lemon• strip of copper• strip of zinc• voltmeter

1. Have students firmly roll thelemon on a hard surface tobreak up some of the juicesacs inside it.

2. Instruct students to stick thestrips of copper and zinc intothe lemon so that the stripsare close together but nottouching.

3. Tell students to fasten analligator clip to each stripand plug the other end intothe appropriate slot in thevoltmeter.

4. Have students record theirresults.

Discuss the results with yourstudents.l Visual ee

CONNECTION toCONNECTION toLife Science ----------------------------g

Nerves We use electrolytes inour bodies as well. In biology,electrolytes are considered sub-stances that can conduct anelectric current when they are insolution. Electrolytes in thebody include sodium ions andpotassium ions in body fluids.Different concentrations of theseions inside and outside nervecells enable nerve cells to con-duct electrical impulses. Use theteaching transparency “What Isa Nerve?” to teach studentsmore about nerves.


wet cells and dry cellsCHAPTER RESOURCES

Technology

Transparencies• P70 How a Cell Produces an Electric Current

• LINK TOLINK TO LIFE SCIENCELIFE SCIENCE L90 What Is a Nerve?


Copper wire

Burner

Iron wire

Ice water

Currentmeter

Figure 9 In a simple thermocouple, one section of the loop is heated and one section is cooled.

thermocouple a device that con-verts thermal energy into electrical energy

photocell a device that converts light energy into electrical energy

For another activity related to this chapter, go to go.hrw.com and type in the keyword HP5ELEW.

ThermocouplesThermal energy can be converted into electrical energy by a thermocouple. A simple thermo couple, shown in Figure 9, is made by joining wires of two different metals into a loop. The temperature difference within the loop causes charges to flow through the loop. The greater the temperature difference is, the greater the current is. Thermocouples usually do not generate much energy. But they are useful for monitoring the temperatures of car engines, furnaces, and ovens.

PhotocellsIf you look at a solar-powered calculator, you will see a dark strip called a solar panel. This panel is made of several photocells. A photocell converts light energy into electrical energy. How do photocells work? Most photocells contain silicon atoms. As long as light shines on the photocell, electrons gain enough energy to move between atoms. The electrons are then able to move through a wire to provide electrical energy to power a device, such as a calculator.

In larger panels, photocells can provide energy to buildings and cars. Large panels of photocells are even used on satellites. By changing light energy from the sun into electrical energy, the photocells provide energy to the many devices on the satellite to keep the devices working.

✓Reading Check What device converts light energy into electri-cal energy?


Reteaching -------------------------------------bResistance To help students having difficulty understanding resistance, take the entire class out to a school hallway. Ask stu-dents the following question: “If 100 students raced to the exit, which would offer less resistance to their movement: a narrow hallway or a wide hallway?”

Referring to Ohm’s law, make sure students understand that as resistance decreases, current (the rate at which charges flow) increases. l Logical

Quiz ---------------------------------------------------------------------g

1. What are two factors that affect the amount of electric current in a wire? (voltage and resistance)

2. Explain the difference between wet cells and dry cells. (Wet cells contain a liquid electrolyte, such as sulfuric acid. Dry cells, such as flashlight cells, contain solid or pastelike electrolytes.)


Making Models Supply stu-dents with materials to construct a model of a cell. The materials could include colored construc-tion paper, foam board, markers, and ice-cream sticks. Instruct students that their model should include all parts of a cell, as well as labels for each part. l Visual ee Answer to Reading Check

a photocell


SummarySummary

A B

Review

• Electric current is the rate at which charges pass a given point.

• An electric current can be made when there is a potential difference between two points.

• As voltage, or potential difference increases, current increases.

• An object’s resistance varies depending on the object’s material, thickness, length, and temperature. As resistance increases, current decreases.

• Cells and batteries convert chemical energy or radiant energy into electrical energy.

• Thermocouples and photocells are devices used to generate electrical energy.

Topic: Electric CurrentSciLinks code: HSM0472

Critical Thinking

10. Making Comparisons A friend is having trouble studying the types of cells in this section. Explain to your friend how the terms photocell and thermocouple hold clues that can help him or her remember the type of energy taken in by each device.

11. Making Inferences Why do you think some calculators that contain photocells also contain batteries?

12. Applying Concepts Which wire would have the lowest resistance: a long, thin iron wire at a high temperature or a short, thick copper wire at a low temperature?


13. The wires shown below are made of copper and have the same temperature. Which wire should have the lower resistance? Explain your answer.

Using Key Terms

Complete each of the following sentences by choosing the correct term from the word bank.

voltage electric currentresistance cell

1. The rate at which charges pass a point is a(n) .

2. The opposition to the flow of charge is .

3. Another term for potential difference is .

4. A device that changes chemical energy into electrical energy is a(n) .


5. Which of the following factors affects the resistance of an object?

a. thickness of the objectb. length of the objectc. temperature of the objectd. All of the above

6. Name the parts of a cell, and explain how they work together to produce an electric current.

7. Compare alternating current with direct current.

8. How do the currents produced by a 1.5 V flash-light cell and a 12 V car battery compare if the resistance is the same?

9. How does increasing the resistance affect the current?



1. electric current2. resistance3. voltage4. cell5. d6. A cell is made of an elec-

trolyte and two electrodes. Chemical reactions in the elec-trolyte leave extra electrons on one electrode and strip them from the other. If the charged electrodes are connected with a wire, electric charges will flow between them.

7. Charges in an alternating current reverse direction many times a second. Charges in direct current move in only one direction.

8. Under equal conditions, the current from a 12 V car battery is greater than the current from a 1.5 V flashlight cell. (Students will learn in the next section that resistance might change this comparison.)

9. Increasing the resistance decreases the current.

10. Sample answer: The prefix photo- refers to light, as in the terms photosynthesis or photo-graph. So, a photocell must take in light energy. The prefix thermo- refers to heat, as in the term thermometer. So, a thermo-couple must take in thermal energy.

11. Some solar calculators contain batteries as a backup power source, for when there is not enough light.

12. A short, thick copper wire at a low temperature would have a lower resistance than a long, thin iron wire at a high temperature.

13. Wire A should have the lower resistance because it is shorter than wire B. The resistance of a wire increases as the length of the wire increases.

CHAPTER RESOURCES


• Section Quiz g • Section Review g • Vocabulary and Section Summary g

CRF

Current Versus Voltage

Voltage (V)

Curr

ent

(A)

2.0

2.5

1.5

1.0

0.5

0.00 10 20 30 40 50

Current Versus Resistance at Constant Voltage

Resistance (Ω)

Curr

ent

(A)

16

20

12

8

4

00 4 8 12 16 20

READING STRATEGY

Electrical CalculationsA German school teacher named Georg Ohm wondered howelectric current, voltage, and resistance are related.

Connecting Current, Voltage, and ResistanceOhm (1789–1854) studied the resistances of materials. He mea-sured the current that resulted from different voltages appliedto a piece of metal wire. The graph on the left in Figure 1 issimilar to the graph of his results.

Ohm’s LawOhm found that the ratio of voltage (V ) to current (I ) is aconstant for each material. This ratio is the resistance (R) ofthe material. When the voltage is expressed in volts (V) andthe current is in amperes (A), the resistance is in ohms ().The equation below is often called Ohm’s law because of Ohm’swork.

As the resistance goes up, the current goes down. And asthe resistance decreases, the current increases. The second graphin Figure 1 shows this relationship. Notice that if you multiplythe current and the resistance for any point, you get 16 V.

R � , or V � I � RVI

3

Figure 1 The relationship between current and voltage isdifferent from the relationship between current and resistance.

What You Will Learn

Use Ohm’s law to calculate voltage,current, and resistance.Calculate electric power.Determine the electrical energy usedby a device.

Vocabularyelectric power

Paired Summarizing Read thissection silently. In pairs, take turnssummarizing the material. Stop todiscuss ideas that seem confusing.

OverviewIn this section, students learnhow to calculate resistance,voltage, and current usingOhm’s law. Students also learnabout electric power andelectrical energy.

BellringerWrite the following question onthe board: “How fast is a nano-second?” Discuss studentresponses, and tell them that ananosecond (ns) is one-billionthof a second. Then, explain thatelectrical signals travel at30 cm/ns. Hold up a ruler togive students a visual image of30 cm. Have students calculatehow far electrical signals travelin 1 s.

Demonstration ------------------bCurrent and Amps Set up a100 W light bulb at the frontof the classroom. Turn the lighton, and explain to students thatthe amount of current in thebulb is 1 amp. Ask students toguess how many amps a toasteruses (10 amps) and how manyamps a television set uses(3 amps). Encourage studentsto offer explanations for thesediffer ences. l Visual

3

MISCONCEPTIONALERT

Nonohmic Materials Materials thatdo not obey Ohm’s law are called non-ohmic materials. Semiconductors areexamples of nonohmic materials.

CHAPTER RESOURCES



Technology

Transparencies• Bellringer

Workbooks



100

Electric PowerThe rate at which electrical energy is changed into otherforms of energy is electric power. The unit for power isthe watt (W), and the symbol for power is the letter P.Electric power is expressed in watts when the voltageis in volts and the current is in amperes. Electric poweris calculated by using the following equation:

power � voltage � current, or P � V � I

Watt: The Unit of PowerIf you have ever changed a light bulb, you prob-ably know about watts. Light bulbs, such as theones in Figure 2, have labels such as “60 W,”“75 W,” or “120 W.” As electrical energy issupplied to a light bulb, the light bulb glows.As power increases, the bulb burns brighterbecause more electrical energy is convertedinto light energy. The higher power rating ofa 120 W bulb tells you that it burns brighterthan a 60 W bulb.

Another common unit of power is the kilo-watt (kW). One kilowatt is equal to 1,000 W.Kilowatts are used to express high values ofpower, such as the power needed to heat ahouse.

✓Reading Check What are two common unitsfor electric power? (See the Appendix for answers toReading Checks.)

electric power the rate at whichelectrical energy is converted intoother forms of energy

Using Ohm’s Law What is the voltage if the currentis 2 A and the resistance is 12 ?

Step 1: Write the equation for voltage.

V � I � R

Step 2: Replace the current and resistance with themeasurements given in the problem, andsolve.

V � 2 A � 12

V � 24 V

Now It’s Your Turn1. Find the voltage if the current is 0.2 A and

the resistance is 2 .2. The resistance of an object is 4 . If the

current in the object is 9 A, what voltagemust be used?

3. An object has a resistance of 20 . Calculatethe voltage needed to produce a current of0.5 A.

Figure 2 These light bulbs have differentwattages, so they use different amounts ofelectric power.

CONNECTIONCONNECTION vvMath -----------------------------------------------------------g

Electric Power In the passageabout electric power, refer to theequation:

power (watts) � voltage (volts) �

current (amperes)

Have students solve the twoproblems below.

1. A toaster draws approximately10 A of current. A homereceives 120 V at each electri-cal outlet. What is the powerof the toaster? (10 A � 120 V �

1,200 W)

2. A car uses a 12 V battery. Oneheadlight draws about 3 A.What is the power of theheadlight? (12 V � 3 A � 36 W)

l Logical

Answers to Math Focus

1. 0.4 V2. 36 V3. 10 V


watt (W) and kilowatt (kW)

CHAPTER RESOURCESWorkbooks

Math Skills for Scienceg• Multiplying Whole Numbers

SUPPORT FOR

English Language LearnersOhm’s Law Paraphrase can promoteand demonstrate student comprehen-sion. After students have read aboutOhm’s Law, ask groups of 3 studentsto prepare a brief paraphrase. Then,have pairs of groups share their para-phrases with each other orally. Theyshould combine their explanations tomake sure there is no missing or inac-curate information. Invite a volunteerfrom each paired group to share thegroup paraphrase orally with the class.l Verbal/Interpersonal Section 3 • Electrical Calculations 491

Measuring Electrical EnergyElectric power companies sell electrical energy to homes and businesses. Such companies determine how much a home or business has to pay based on power and time. For example, the amount of electrical energy used in a home depends on the power of the electrical devices in the house and the length of time that those devices are on. The equation for electrical energy is as follows:

electrical energy � power � time, or E � P � t

Measuring Household Energy UseDifferent amounts of electrical energy are used each day in a home. Electric companies usually calculate electrical energy by multiplying the power in kilowatts by the time in hours. The unit of electrical energy is usually kilowatt-hours (kWh). If 2,000 W (2 kW) of power are used for 3 h, then 6 kWh of energy were used.

Electric power companies use meters, such as the one in Figure 3, to determine how many kilowatt-hours of energy are used by a household. These meters are often outside of buildings so that someone from the power company can read them.

✓Reading Check What unit of measurement is usually used to express electrical energy?

Power and Energy A small television set draws a current of 0.42 A at 120 V. What is the power rating for the television? How much energy is used if the television is on for 3 h?

Step 1: Write the equation for power.

P � V � I

Step 2: Replace the voltage and current with the measurements given in the prob-lem, and solve.

P � 120 V � 0.42 A

P � 50.4 W, or 0.0504 kW

Step 3: Write the equation for electrical energy.

E � P � t

Step 4: Replace the power and time with the measurements given in the problem, and solve.

E � 0.0504 kW � 3 h

E � 0.1512 kWh

Now It’s Your Turn1. A computer monitor draws 1.2 A at a

voltage of 120 V. What is the power rating of the monitor?

2. A light bulb draws a 0.5 A current at a voltage of 120 V. What is the power rating of the light bulb?

3. How much electrical energy does a 100 W light bulb use if it is left on for 24 h?

Figure 3 These photographs were taken 10 days apart. According to the dials on the meter, 101 kWh of energy were used.


Reteaching -------------------------------------bConverting Watts Remind stu-dents that they must divide a power rating in watts by 1,000 to convert it into kilowatts for use in calculating electrical energy. Have students pair up and practice the conversion of the power ratings of common light bulbs. l Logical

Quiz ---------------------------------------------------------------------g

1. According to Ohm’s law, what happens to the current if the voltage increases and the resistance stays constant? (Current increases.) If the cur-rent in a wire is 4 A, what is the ratio of the voltage applied to the wire to the wire’s resistance in ohms? (You may wish to have stu-dents read the Math Refresher in the Appendix if they need help with ratios.) (4:1)

2. How do electric power compa-nies keep track of how much electrical energy a household or business uses? (Usually, they use electric meters that record the kilowatt-hours of energy used by a household or a business.)


kilowatt-hour (kWh)Answers to Math Focus

1. 144 W2. 60 W3. 2.4 kWh



SummarySummary

Review

• Ohm’s law describes the relationship between current, resistance, and voltage.

• Electric power is the rate at which electrical energy is changed into other forms of energy.

• Electrical energy is elec-tric power multiplied by time. It is usually expressed in kilowatt-hours.

Using Key Terms

1. In your own words, write a defi-nition for the term electric power.


2. Which of the following is Ohm’s law?

a. E � P � tb. I � V � Rc. P � V � Id. V � I � R

3. Circuit A has twice the resistance of circuit B. The voltage is the same in each circuit. Which circuit has the higher current?

Math Skills

4. Use Ohm’s law to find the volt-age needed to make a current of 3 A in a resistance of 9 .

5. How much electrical energy does a 40 W light bulb use if it is left on for 12 h?

Critical Thinking

6. Applying Concepts Explainwhy increasing the voltage applied to a wire can have the same effect on the current in the wire that decreasing the resis-tance of the wire does.

7. Identifying Relationships Using the equations in this section, develop an equation to find electrical energy from time, current, and resistance.

Topic: Electrical EnergySciLinks code: HSM0475

Saving EnergyWith a parent, identify the power

rating for each light in your home and estimate how long each light is on during a day. In your science journal,determine how much electri-cal energy each light uses per day. Then, describe two ways to save energy with the lights.

How to Save EnergyEvery appliance uses energy. But a fan, such as the one in Figure 4, could actually help you save energy. If you use a fan, you can run an air conditioner less. Replacing items that have high power ratings with items that have lower ratings is another way to save energy. Turning off lights when they are not in use will also help.

Figure 4 Using a fan to stay cool and using a small toaster instead of a larger toaster oven are ways to save energy.

WRITING

SKILL

Section 3 • Electrical Calculations 493

Answer to School-to-Home Activity

Ways to save energy include turning off lights when they are not in use and installing bulbs that are more efficient and have a lower power rating.


Writing Electrical Energy Havestudents write a para-graph about electrical

energy. Tell them to include each of the units of measure-ment discussed in this section (kilowatt-hours, volts, amperes, ohms, watts). Have them read their finished paragraph aloud.l Visual


1. Sample answer: Electric power is how fast electrical energy is changed into other forms of energy.

2. d3. Circuit B4. V � I � R � 3 A � 9 Ω � 27 V5. E � P � t � 0.040 kW � 12 h �

0.48 kWh6. Increasing the voltage applied to

a wire will increase the current. Reducing the resistance of the wire would also increase the current.

7. Substituting P � V � I into E � P � t results in the equation E � V � I � t. Substituting V � I � R into the new equation for electrical energy results in the equation E � I � R � I � t.This can be rearranged to E � I 2 � R � t.

CHAPTER RESOURCES


• Section Quiz g • Section Review g • Vocabulary and Section Summary g • Critical Thinking a

CRF

READING STRATEGY

Necessary Parts of a CircuitFigure 1

4 Electric CircuitsThink about a roller coaster. You start out nice and easy. Then, you roar around the track. A couple of exciting minutes later, you are right back where you started!

A roller-coaster car follows a fixed pathway. The ride’s startingpoint and ending point are the same place. This kind of closedpathway is called a circuit.

Parts of an Electric CircuitJust like a roller coaster, an electric circuit always forms aloop—it begins and ends in the same place. Because a circuitforms a loop, a circuit is a closed path. So, an electric circuit isa complete, closed path through which electric charges flow.

All circuits need three basic parts: an energy source, wires,and a load. Loads, such as a light bulb or a radio, are con-nected to the energy source by wires. Loads change electricalenergy into other forms of energy. These other forms mightinclude thermal energy, light energy, or mechanical energy.As loads change electrical energy into other forms, they offersome resistance to electric currents. Figure 1 shows examplesof the parts of a circuit.

✓✓Reading Check What are the three parts of an electric circuit? (See the Appendix for answers to Reading Checks.)

What You Will Learn

Name the three essential parts of acircuit.Compare series circuits with parallelcircuits.Explain how fuses and circuit breakers protect your home againstshort circuits and circuit overloads.

Vocabularyseries circuitparallel circuit

Brainstorming The key idea of thissection is electric circuits. Brainstormwords and phrases related to electriccircuits.

Wires connect the other parts of a circuit. Wires are made of conducting materials that have low resist-ance, such as copper.

The energy sourcecan be a battery, a photocell, a thermo-couple, or an electric generator at a power plant.

Examples of loads arelight bulbs, appliances, televisions, and motors.

OverviewIn this section, students learnthe definition of an electric cir-cuit, the main parts of a circuit,and the difference betweenseries and parallel circuits. Thesection also discusses circuits inthe home and circuit safety.

BellringerWrite the following question onthe board: “What happens whenyou turn the lights on?”

Encourage students to thinkbeyond the obvious. Have themexplain what allows lights to beturned on and off. Havestudents write down theiranswer or draw an explanatorypicture for later reference.

Demonstration --------------gCircuit Building Create a cir-cuit, and demonstrate how itworks to the class. Connect a6 V battery to a small light bulbwith copper wire. Students willobserve that the bulb lights. Askthem to explain why this deviceconstitutes a circuit. (When prop-erly connected, the parts form acomplete path through which electric charges flow.) l Visual


an energy source, wires, and a load CONNECTIONCONNECTION vvLanguage Arts ------------------g

Writing A Circuit Story After studentsunderstand what a circuit is andwhat its parts are, have them write a

short story that includes a circuit in somemeaningful way. For example, a studentcould write about the role of a faulty circuitswitch in solving a mystery or about aworld where circuits behave differentlythan they do in this one. Have interestedstudents read their story to the class.l Verbal

4

CHAPTER RESOURCES



Technology

Transparencies• Bellringer• P71 Parts of a Circuit

Workbooks



Load

Energy source

Wire

Switch

Load

Energy source

Wire

Switch

A Switch To Control a CircuitSometimes, a circuit also contains a switch, such as the one shown in Figure 2. A switch is used to open and close a cir-cuit. Usually, a switch is made of two pieces of conducting material, one of which can be moved. For charges to flow through a circuit, the switch must be closed, or “turned on.” If a switch is open, or “off,” the loop of the circuit is broken. Charges cannot flow through a broken circuit. Light switches, power buttons on radios, and even the keys on calculators and computers open and close circuits.

Types of CircuitsLook around the room. Count the number of objects that use electrical energy. You might have found things, such as lights, a clock, and maybe a computer. All of the things you counted are loads in a large circuit. The circuit may connect more than one room in the building. In fact, most circuits have more than one load.

The loads in a circuit can be connected in different ways. As a result, circuits are often divided into two types. A circuit can be a series circuit or a parallel circuit. One of the main differences in these circuits is the way in which the loads are connected to one another. As you read about each type of circuit, look closely at how the loads are connected.

✓Reading Check What are two types of electric circuits?

When the switch is closed, the two pieces of conducting material touch, which allows the electric charges to flow through the circuit.

When the switch is open, the gap between the two pieces of conducting material prevents the electric charges from traveling through the circuit.

Using a SwitchFigure 2

WRITINGSKILL

Nervous Impulses Believe

it or not, your body is con-trolled and monitored by electrical impulses. Research the electrical impulses that travel between your brain and the muscles and organs in your body. Then, in your science journal, write a one-page comparison of your nervous system and an electric circuit.

Section 4 • Electric Circuits 495

MISCONCEPTIONALERT

When Charges Flow Some students may have difficulty understanding that charges can flow only through a cir-cuit that is “closed,” or com-plete. To help students remember that charges flow only when a circuit is closed, arrange blocks in a circle. Designate one of the blocks as the switch. Pivot this block away from the circle to show students that if the switch is open, the circle is incom-plete. When the switch is closed, the circle (that is, the circuit) is complete again.

StrategiesStrategiesINCLUSIONINCLUSION

• Behavior Control Issues • Developmentally Delayed• Hearing ImpairedGive students a chance to “see” the idea of the flow and interruption of electric cur-rent. Place several books end-to-end about 1/2 in. from the wall. Roll a small ball (about the size of a ping-pong or golf ball) down the indented path created by the space between the book and the wall. Ask students to notice how the ball can roll from the first book to the last book. Explain that electric charges in a circuit also flow freely. Then, ask a student to watch until the ball has started rolling and then pull out a book at about the half-way point. When the ball reaches the point where the book is missing and falls into the opening, point out that the pulling out of the book is similar to the flipping of a switch in an electric circuit because the continuous path is broken, causing the flow to stop. l Visual


series circuits and parallel circuits

Nikola Tesla, who developed the alternating-current system, was known as a brilliant but eccentric inventor. To dispel fears about the safety of his AC system, Tesla would light lamps using himself in place of the wires; the charges flowed through his body instead!

Series CircuitsA series circuit is a circuit in which all parts are connected ina single loop. There is only one path for charges to follow, sothe charges moving through a series circuit must flow througheach part of the circuit.

All of the loads in a series circuit share the same current.The four identical light bulbs in Figure 3 are joined in series.Because the current in each bulb is the same, the lights glowwith the same brightness. But if you add more light bulbs, theresistance of the whole circuit would go up and the currentwould drop. Therefore, all of the bulbs would be dimmer.

✓Reading Check How are loads connected in a series circuit?

Uses for Series CircuitsA series circuit has only one pathway for moving charges. Ifthere is any break in the circuit, the charges will stop flowing.For example, if one light bulb in a series circuit burns out,there is a break in the circuit. None of the light bulbs in thecircuit would light. Using series circuits would not be a veryconvenient way to wire your home. Imagine if your refrigeratorand a lamp were in a series circuit together. Your refrigeratorwould run only when the lamp was on. And when the bulbburns out, the refrigerator would stop working!

But series circuits are useful in some ways. For example,series circuits are useful in wiring burglar alarms. If any part ofthe circuit in a burglar alarm fails, there will be no current inthe system. The lack of current signals that a problem exists,and the alarm will sound.

Figure 3 In this series circuit,the charges flow from the batterythrough each light bulb (load)and finally back to the battery.

series circuit a circuit in which theparts are joined one after anothersuch that the current in each part isthe same

A Series of Circuits1. Connect a 6 V battery

and two flashlightbulbs in a series circuit.Draw a picture of yourcircuit.

2. Add another flashlightbulb in series with theother two bulbs. Howdoes the brightness ofthe light bulbs change?

3. Replace one of the lightbulbs with a burned-outlight bulb. What happensto the other lights in thecircuit? Why?


Loads are connected in a singleloop in a series circuit.


• battery, 6 V• flashlight bulb, burned-out• flashlight bulb with holder (3)• screwdriver• tape• wire, copper, insulated with ends

stripped (5)

Safety Caution: Remindstudents not to touch theends of the wire and to useonly the screwdriver to con-nect the wire to the bulbholders. Also, make sure thatstudents do not connect thebattery to itself (with noload), as this could create ashort circuit. Have all stu-dents wear safety goggles.

Answers

1. The drawing of the circuitshould show the light bulbsand the 6 V battery connectedin a loop.

2. The light bulbs do not glow asbrightly as they did when onlytwo bulbs were attached.

3. The other light bulbs in the cir-cuit do not glow. The burned-out bulb causes a break in thecircuit, so no charges canflow.

MISCONCEPTIONALERT

Cannot Run Out of Charge Studentsmay think that charges are “used up” asthey pass through a circuit. Reinforcethat charge must be conserved. Chargesthat enter a device, such as a light bulb,must also leave the device.

SUPPORT FOR

English Language LearnersCircuit Diagrams Students will havea better understanding of how circuitsfunction if they create a visual aid andto have for reference. Have studentsdraw and label two diagrams of seriescircuits; one with two light bulbs andone with three. Elicit from studentswhat parts they will need to draw andlabel, writing each term on the board asstudents mention it: load, wire, switch,energy source. Have them add notesnext to each part of the diagram to helpthem remember what it does.l Visual496 Chapter 17 • Introduction to Electricity

Parallel CircuitsThink about what would happen if all of the lights in your home were connected in series. If you needed to turn on a light in your room, all other lights in the house would have to be turned on, too! Instead of being wired in series, circuits in buildings are wired in parallel. A parallel circuit is a circuit in which loads are connected side by side. Charges in a parallel circuit have more than one path on which they can travel.

Unlike the loads in a series circuit, the loads in a parallel circuit do not have the same current. Instead, each load in a parallel circuit uses the same voltage. For example, each bulb in Figure 4 uses the full voltage of the battery. As a result, each light bulb glows at full brightness no matter how many bulbs are connected in parallel. You can connect loads that need dif-ferent currents to the same parallel circuit. For example, you can connect a hair dryer, which needs a high current to run, to the same circuit as a lamp, which needs less current.

✓Reading Check How are loads connected in a parallel circuit?

Uses for Parallel CircuitsIn a parallel circuit, each branch of the circuit can work by itself. If one load is broken or missing, charges will still run through the other branches. So, the loads on those branches will keep working. In your home, each electrical outlet is usually on its own branch and has its own switch. Imagine if each time a light bulb went out your television or stereo stopped working. With parallel circuits, you can use one light or appliance at a time, even if another load fails.

Figure 4 In this parallel circuit, the electric charges flow from the battery and branch off through each bulb. The charges then flow back to the battery.

parallel circuit a circuit in which the parts are joined in branches such that the potential difference across each part is the same

A Parallel Lab1. Connect a 6 V battery

and two flashlight bulbs in a parallel circuit. Draw a picture of your circuit.

2. Add another flashlight bulb in parallel with the other two bulbs. How does the brightness of the light bulbs change?

3. Replace one of the light bulbs with a burned-out light bulb. What happens to the other lights in the circuit? Why?



Loads are connected side by side in branches in a parallel circuit.


• battery, 6 V• flashlight bulb, burned-out• flashlight bulb with holder (3)• screwdriver• tape• wire, copper, insulated with ends stripped, long (2)• wire, copper, insulated with ends

stripped, short (6)

Safety Caution: Tell stu-dents not to touch the ends of the wire and to use only the screwdriver to connect the wire to the light bulbs. Make sure that they do not connect the battery to itself (with no load), as this could create a short circuit. Also, have all students wear safety goggles.

Answers

1. The drawing of the circuit should show the light bulbs on different branches.

2. The light bulbs glow with the same brightness as they did when only two bulbs were attached.

3. The other light bulbs in the circuit still glow because charges can flow through the other branches.

h-----------------------------g

PORTFOLIO

Making a Poster Have students research to

learn more about series circuits and parallel circuits and make a poster presenting their research. Students should point out the advantages and disadvantages of each type of circuit and make recommendations for when to use each type of circuit. Posters should be clear and easy to read. Then, have students share their posters with the class. l Visual

GroupGroup vv -------g

Concept Mapping Have students, in groups, create a concept map to describe what they have learned about electricity. Have the map begin with the topic electricity. Students should use the terms and concepts learned in this chapter to describe the many aspects of this broad topic. Encourage students to link as many terms as possible with appropriate phrases. l Visual/Logical cc

Is That a Fact!A voltmeter is an instrument used in electrical work to measure the voltage between two conductors. Car mechan-ics, electricians, and industrial techni-cians routinely use voltmeters in their work.

Household Circuit SafetyIn every home, several circuits connect all of the lights, appli-ances, and outlets. The circuits branch out from a breaker box or a fuse box that acts as the “electrical headquarters” for the building. Each branch receives a standard voltage, which is 120 V in the United States.

Circuit FailureBroken wires or water can cause a short circuit. In a short circuit, charges do not go through one or more loads in the circuit. The resistance decreases, so the current increases. The wires can heat up, and the circuit could fail. The wires might even get hot enough to start a fire. Circuits also may fail if they are overloaded. When too many loads are in a circuit, the current increases, and a fire might start. Safety features, such as fuses and circuit breakers, help prevent electrical fires.

FusesA fuse has a thin strip of metal. The charges in the circuit flow through this strip. If the current is too high, the metal strip melts, as shown in Figure 5. As a result, the circuit is broken, and charges stop flowing.

Circuit BreakersA circuit breaker is a switch that automatically opens if the current is too high. A strip of metal in the breaker warms up, bends, and opens the switch, which opens the circuit. Charges stop flowing. Open circuit breakers can be closed by flipping a switch after the problem has been fixed.

A ground fault circuit interrupter (GFCI), shown in Figure 6,acts as a small circuit breaker. If the current in one side of an outlet differs even slightly from the current in the other side, the GFCI opens the circuit and the charges stop flowing. To close the circuit, you must push the reset button.

✓Reading Check What are two safety devices used in circuits?

Figure 5 The blown fuse on the left must be replaced with a new fuse, such as the one on the right.

Figure 6 GFCIs are often found on outlets in bathrooms and kitchens to protect you from electric shock.


Reteaching -------------------------------------bFlashcards Students may have difficulty remembering the parts of a series or parallel circuit. To help them, make flashcards with the words battery, series, paral-lel, and bulb, and make cards that represent wires. Help them arrange the cards in proper order. l Visual/Kinesthetic

Quiz ---------------------------------------------------------------------g

Ask students whether these statements are true or false.

1. If a switch is closed, charges flow through the circuit. (true)

2. The loads in a parallel circuit do not necessarily all have the same amount of current in them. (true)

3. When a short circuit occurs, resistance increases and cur-rent decreases. (false)


Writing Section Summary Have students write a one-page synopsis of the concepts

covered in this section. Tell them that their synopsis should read like an essay and that it should be understandable to someone with little prior expo-sure to the material. l Verbal


fuses and circuit breakers

Is That a Fact!Thomas Edison’s famous quotation, “Genius is one percent inspiration, ninety-nine percent perspiration,” is rep-resentative of his dedication and devo-tion to work. Edison and his assistants performed 1,200 experiments in an attempt to find the best material to use as a filament in light bulbs.

Among the fibers he tested were bay-wood, boxwood, hickory, cedar, flax, and bamboo. Finally, in 1879, Edison dis-covered that carbonized cotton thread—cotton sewing thread that has been burned to an ash—worked well. The light bulb that used a carbonized cotton filament burned for 2 days.


A

B

SummarySummary

Review

Electrical Safety TipsYou use electrical devices every day. So, remembering that using electrical energy can be hazardous is impor-tant. Warning signs, such as the one in Figure 7, canhelp you avoid electrical dangers. To stay safe while you use electrical energy, follow these tips:

• Make sure the insulation on cords is not worn.

• Do not overload circuits by plugging in too many electrical devices.

• Do not use electrical devices while your hands are wet or while you are standing in water.

• Never put objects other than a plug into an elec-trical outlet.

• Circuits consist of an energy source, a load, wires, and, in some cases, a switch.

• All parts of a series cir-cuit are connected in a single loop. The loads in a parallel circuit are on separate branches.

• Circuits fail through a short circuit or an over-load. Fuses or circuit breakers protect against circuit failure.

• It is important to follow safety tips when using electrical energy.

Using Key Terms

1. In your own words, write a definition for each of the following terms: series circuit and parallel circuit.


2. Which part of a circuit changes electrical energy into another form of energy?

a. energy sourceb. wirec. switchd. load

3. Name and describe the three essential parts of a circuit.

4. How do fuses and circuit breakers protect your home against electrical fires?

Critical Thinking

5. Forming Hypotheses Supposethat you turn on the heater in your room and all of the lights in your room go out. Propose a reason why the lights went out.

6. Applying Concepts Will a fuse work successfully if it is connected in parallel with the device it is supposed to protect? Explain your answer.


7. Look at the circuits below. Iden-tify each circuit as a parallel circuit or a series circuit.

Topic: Electric CircuitsSciLinks code: HSM0471

Figure 7 Obeyingsigns that warn of high voltage can keep you safe from electrical dangers.



1. Sample answer: A series circuit is a circuit in which the loads are joined one after another like the cars of a train. A parallel circuit is a circuit in which the loads are joined so that each load is on its own branch, like the wooden railroad ties under train tracks.

2. d3. The energy source provides

electrical energy. The load is any device that uses the electrical energy to do work. Wires con-nect the energy source to the load.

4. Fuses and circuit breakers cre-ate breaks in a circuit when the current gets too high, preventing charges from flowing. “Breaking” the circuit prevents overheating and fires.

5. One possible reason is that there is a short circuit in the heater. Another possible reason is that the heater, along with any other devices attached to the circuit, overloads the circuit and trips the breaker.

6. No, a fuse in parallel with the device it is supposed to protect will not work successfully. If the fuse should blow, it would open only the branch that the fuse is on. The device will continue run-ning because it is on a separate branch.

7. The circuit in A is a series cir-cuit. The circuit in B is a parallel circuit.

CHAPTER RESOURCES


• Section Quiz g • Section Review g • Vocabulary and Section Summary g • Reinforcement Worksheet b • Critical Thinking a • SciLinks Activity g • Datasheet for Quick Lab

CRF

LabSkills Practice

Build a series circuit and a parallel circuit.

Use Ohm’s law to calculate the resistance of a circuit from voltage and current.

• ammeter

• energy source—dry cell(s)

• light-bulb holders (3)

• light bulbs (3)

• switch

• voltmeter

• wire, insulated, 15 cm lengths with both ends stripped

Circuitry 101There are two basic types of electric circuits. A series circuit connects all of the parts in a single loop, and a parallel circuit connects each part on a separate branch. A switch wired in series with the energy source can control the whole circuit. If you want each part of the circuit to work on its own, the loads must be wired in parallel. In this lab, you will use an ammeter to measure current and a voltmeter to measure voltage. For each circuit, you will use Ohm’s law (resistance equals voltage divided by current) to determine the overall resistance.

Procedure

1 Build a series circuit with an energy source, a switch, and three light bulbs. Draw a diagram of your circuit. Caution: Always leave the switch open when building or changing the circuit. Close the switch only when you are test-ing or taking a reading.

2 Test your circuit. Do all three bulbs light up? Are all bulbs the same brightness? What happens if you carefully unscrew one light bulb? Does it make any difference which bulb you unscrew? Record your observations.

3 Connect the ammeter between the power source and the switch. Close the switch, and record the current on your dia-gram. Be sure to show where you measured the current.

4 Reconnect the circuit so that the ammeter is between the first and second bulbs. Record the current, as you did in step 3.

5 Move the ammeter so that it is between the second and third bulbs, and record the current again.

6 Remove the ammeter from the circuit. Connect the voltmeter to the two ends of the power source. Record the voltage on your diagram.

7 Use the voltmeter to measure the voltage across each bulb. Record each reading.

8 Take apart your series circuit. Reassemble the same items so that the bulbs are wired in parallel. (Note: The switch must remain in series with the power source to be able to control the whole circuit.) Draw a diagram of your circuit.

MATERIALS

OBJECTIVES

SAFETY


Skills PracticeSkills Practice LabLab

Circuitry 101

Teacher’s NotesTeacher’s Notes

Time RequiredTwo 45-minute class periods

Lab Ratings

rTeacher Prep ff

Student Set-Up ff

Concept Level fff

Clean Up f

M A T E R I A L SMaterials listed are for each group of 3–5 students. Use a series of three 1.5 V cells or a 6 V battery as a power source. If you use a series of 1.5 V cells, create a single battery by taping the cells together (positive to negative). Use only regular dry cell or alkaline batteries. Do not use nicad or lithium batteries.

Safety CautionRemind students to review all safety cautions and icons before beginning this lab activity. Caution students that the meters can be damaged if connected improperly.

Procedure NotesTell or show students how to build a circuit. Demonstrate the proper way to use an ammeter and a voltmeter. You may wish to perform this lab as a demon-stration if materials are limited.

Disposal InformationRegular dry cell or alkaline flashlight bat-teries (or regular 6 V batteries) can be dis-posed of in normal trash containers. Nicad and lithium batteries are toxic and should not be used.

CHAPTER RESOURCES


CRF • Datasheet for Chapter Lab• Lab Notes and Answers

Technology

Classroom Videos• Lab Video

• Stop the Static Electricity! • Potato Power

9 Test your circuit, and record your observations,as you did in step 2.

0 Connect the ammeter between the powersource and the switch. Record the current.

q Reconnect the circuit so that the ammeter isright next to one of the three bulbs. Record thecurrent.

w Repeat step 11 for the two remaining bulbs.

e Remove the ammeter from your circuit.Connect the voltmeter to the two ends of thepower source. Record the voltage.

r Measure and record the voltage across eachlight bulb.

Analyze the Results

1 Recognizing Patterns Was the current thesame at all places in the series circuit? Was itthe same everywhere in the parallel circuit?

2 Analyzing Data For each circuit, compare thevoltage across each light bulb with the voltageat the power source.

3 Identifying Patterns What is the relation-ship between the voltage at the power sourceand the voltages at the light bulbs in a seriescircuit?

4 Analyzing Data Use Ohm’s law and thereadings for current (I) and voltage (V) at thepower source for both circuits to calculate thetotal resistance (R) in both the series and par-allel circuits.

Draw Conclusions

5 Drawing Conclusions Was the total resis-tance for both circuits the same? Explain youranswer.

6 Interpreting Information Why did the bulbsdiffer in brightness?

7 Making Predictions Based on your results,what do you think might happen if too manyelectrical appliances are plugged into the sameseries circuit? What might happen if too manyelectrical appliances are plugged into the sameparallel circuit?

Analyze the Results

1. The current was the same at allpoints in the series circuit. Thecurrent was not the same at allpoints in the parallel circuit.

2. The voltage across each lightbulb in the series circuit wasabout the same and less thanthe voltage at the power source.The voltage across each lightbulb in the parallel circuit wasthe same as the voltage at thepower source.

3. The voltage at the power sourceis the sum of the voltages at thelight bulbs in a series circuit.

4. Answers will depend on thebulbs used. Check for correctcalculations.

Draw Conclusions

5. No, the series circuit had amuch higher resistance than theparallel circuit did. The resis-tance is less in a parallel circuitbecause the electric current hasmore than one path to follow.

6. The parallel circuit had brighterbulbs because the voltageacross each bulb was greaterthan in the series circuit.

7. Too many appliances on thesame series circuit would causeeach appliance to get very littlevoltage, so they may not receiveenough electric current to work.Too many appliances on thesame parallel circuit couldcause too much electric currentin the circuit (because all loadsin a parallel circuit draw thesame voltage), leading to anoverloaded circuit.

CHAPTER RESOURCESWorkbooks

Whiz-Bang Demonstrations• Hoop It Upa• Bending Watera

Long-Term Projects & Research Ideas• The Future Is Electrica

Calculator-Based Labs• Lemon “Juice”a

David Sparks

Redwater Junior HighRedwater, Texas

Holt Lab Generator CD-ROMSearch for any lab by topic, standard, difficulty level,or time. Edit any lab to fit your needs, or create yourown labs. Use the Lab Materials QuickList softwareto customize your lab materials list.

CLASSROOM

TESTED& APPRO

VED

Chapter 17 • Chapter Lab 501

The statements below are false. For each statement, replace the underlined term to make a true statement.

1 Charges fl ow easily in an electricalinsulator.

2 Lightning is a form of static electricity.

3 A thermocouple converts chemical energy into electrical energy.

4 Voltage is the opposition to the cur-rent by a material.

5 Electric force is the rate at which elec-trical energy is converted into other forms of energy.

6 Each load in a parallel circuit has the same current.

Multiple Choice

7 Two objects repel each other. What charges might the objects have?

a. positive and positiveb. positive and negativec. negative and negatived. Both (a) and (c)

8 Which device converts chemical energy into electrical energy?

a. lightning rodb. cellc. light bulbd. switch

9 Which of the following wires has the lowest resistance?

a. a short, thick copper wire at 25°Cb. a long, thick copper wire at 35°Cc. a long, thin copper wire at 35°Cd. a short, thick iron wire at 25°C

0 An object becomes charged when the atoms in the object gain or lose

a. protons.b. neutrons.c. electrons.d. All of the above

q Which of the following devices does NOT protect you from electrical fi res?

a. electric meterb. circuit breakerc. fused. ground fault circuit interrupter

wFor a cell to produce a current, the electrodes of the cell must

a. have a potential difference.b. be in a liquid.c. be exposed to light.d. be at two different temperatures.

e The outlets in your home provide

a. direct current.b. alternating current.c. electric discharge.d. static electricity.

USING KEY TERMS

UNDERSTANDING KEY IDEAS

Assignment GuideSECTION QUESTIONS

1 1–2, 7, 10, 15, 25–26

2 3–4, 8–9, 12–13, 16, 24

3 5, 17–21

4 6, 11, 14, 23

2 and 4 22

ANSWERS

Using Key Terms1. electrical conductor2. electric discharge3. cell4. Resistance5. Electric power6. series circuit

Understanding Key Ideas7. d8. b9. a

10. c11. a12. a13. b


CHAPTER RESOURCES


CRF • Chapter Reviewg• Chapter Test Ag• Chapter Test Ba• Chapter Test Cs• Vocabulary Activityg

Workbooks

Study Guide• Study Guide is also available in Spanish.

Short Answer

r Describe how a switch controls acircuit.

t Name the two factors that affect thestrength of electric force, and explainhow they affect electric force.

y Describe how direct current differsfrom alternating current.

Math Skills

u What voltage is needed to producea 6 A current in an object that has aresistance of 3 1?

i Find the current produced when avoltage of 60 V is applied to a resis-tance of 15 1.

o What is the resistance of an object ifa voltage of 40 V produces a currentof 5 A?

p A light bulb is rated at 150 W. Howmuch current is in the bulb if 120 V isapplied to the bulb?

aHow much electrical energy does a60 W light bulb use if it is used for1,000 hours?

sConcept Mapping Use the followingterms to create a concept map: electriccurrent, battery, charges, photocell, ther-mocouple, circuit, parallel circuit, andseries circuit.

dMaking Inferences Suppose your sci-ence classroom was rewired over theweekend. On Monday, you notice thatthe lights in the room must be on forthe fi sh-tank bubbler to work. And ifyou want to use the computer, youmust turn on the overhead projector.Describe what mistake the electricianmade when working on the circuits inyour classroom.

fApplying Concepts You can make a cellby using an apple, a strip of copper,and a strip of silver. Explain how youwould construct the cell, and identifythe parts of the cell. What type of celldid you make? Explain your answer.

gApplying Concepts Your friend showsyou a magic trick. First, she rubs aplastic pipe on a piece of wool. Then,she holds the pipe close to an emptysoda can that is lying on its side.When the pipe is close to the can, thecan rolls toward the pipe. Explain howthis trick works.

h Classify the objects in the photographbelow as electrical conductors or elec-trical insulators.

CRITICAL THINKING

INTERPRETING GRAPHICS

16. The charges in direct currentflow in one direction. In alter-nating current, the chargescontinually switch from flowingin one direction to flowing inthe reverse direction.

17. V � I � R � 6 A � 3 � 18 V18. I � V/R � 60 V/15 � 4 A19. R � V/I � 40 V/5 A � 8

20. I � P/V � 150 W/120 V �1.25 A

21. E � P � t �0.06 kW � 1,000 h � 60 kWh

Critical Thinking22. An answer to this

exercise can befound at the endof this book.

23. The electrician must have wiredthe fish-tank bubbler in serieswith the lights and the com-puter in series with the over-head projector.

24. You would push the strip ofcopper and the strip of silverinto the apple. The apple is theelectrolyte, and the metal stripsare the electrodes. Studentsmay identify the cell as a drycell because the apple is a solidor as a wet cell because theapple juice conducts the elec-tric current.

25. When the pipe is rubbed with apiece of wool, the pipe ischarged by friction. When thecharged pipe is held close tothe can, the charges in the canare rearranged and the can ischarged by induction. The sideof the can closest to the pipehas the opposite charge thatthe pipe has, and the can isattracted to the pipe.

Interpreting Graphics26. conductors: tap water in glass,

wrench, metal part of scissors,liquid soap in plastic bottle;insulators: basketball, glass,plastic bottle, plastic scissorshandles, wooden table

14. When a switch is open, it creates a break inthe circuit. Charges cannot flow in the cir-cuit. When a switch is closed, it closes thegap in the circuit. The circuit is complete,so charges can flow in it.

15. One factor is the amount of the electriccharge. The greater the charge is, thegreater the force. The other factor is thedistance between the charges. The closerthe charges are to each other, the greaterthe force between them.

Chapter 17 • Chapter Review 503

READING

MISCONCEPTIONALERT

Answers to the standardized test preparation can help you identify student misconcep-tions and misunderstandings.

Teacher’s NoteTeacher’s NoteTo provide practice under more realistic testing conditions, give students 20 minutes to answer all of the questions in this Standardized Test Preparation.

READINGRead each of the passages below. Then, answer the questions that follow each passage.

Passage 1 In 1888, Frank J. Sprague developed a way to operate trolleys by using electrical energy. These electric trolleys ran on a metal track and were connected by a pole to an overhead power line. Electric charges flowed down the pole to motors in the trolley. A wheel at the top of the pole, called a shoe, rolled along the power line and allowed the trolley to move along its track without losing contact with its source of electri-cal energy. The charges passed through the motor and then returned to a generator by way of the metal track.

1. In this passage, what does the word shoemean?

A a type of covering that you wear on your foot

B a device that allowed a trolley to get electrical energy

C a fl at, U-shaped metal plate nailed to a horse’s hoof

D the metal track on which trolleys ran

2. What is the main purpose of this passage?

F to inform the readerG to infl uence the reader’s opinionH to express the author’s opinionI to make the reader laugh

3. Which of the following statements describes what happens fi rst in the operation of a trolley?

A Charges fl ow down the pole.B Charges pass through the motor.C Charges enter the shoe from the power line.D Charges return to the generator through the

tracks.

Passage 2 Benjamin Franklin (1706–1790) first suggested the terms positive and negative for the two types of charge. At the age of 40, Franklin was a successful printer and journalist. He saw some experiments on electricity and was so fascinated by them that he began to devote much of his time to experimenting. Franklin was the first person to realize that lightning is a huge electric discharge, or spark. He invented the first lightning rod, for which he became famous. He also flew a kite into thunderclouds—at great risk to his life—to collect charge from them. During and after the Revolutionary War, Franklin gained fame as a politician and a statesman.

1. Which of the following happened earliest in Franklin’s life?

A He gained fame as a politician.B He fl ew a kite into thunderclouds.C He saw experiments on electricity.D He was a successful journalist.

2. Which of the following statements is a fact according to the passage?

F Franklin became interested in electricity in 1706.

G There is no connection between lightning and an electric discharge.

H Franklin became a successful journalist after he performed experiments with electricity.

I Flying a kite into thunderclouds is dangerous.

Passage 11. B2. F3. C

Question 1: The meanings of the word shoe that are most familiar to students are a type of covering that is worn on the feet or a flat, U-shaped metal plate nailed to a horse’s hoof. However, as it is used in this passage, a shoe is a device that allowed a trol-ley to get electrical energy. Students might answer that it is the metal track on which trolleys ran because the sentence in which shoe appears also describes the track.

Passage 21. D2. I Question 1: Franklin was a successful journal-

ist at the age of 40 before he saw experiments on electricity. He did not fly a kite into thunderclouds until after his interest in electricity was sparked by seeing the experiments. He gained fame as a politi-cian late in life. In 1776, the time of the Revolutionary War, he was 70 years old.


Sta

nd

ard

ized

Test P

rep

ara

tion

1. Opening which switch will turn off only light bulb 2?

A switch 1B switch 2C switch 3D switch 4

2. Opening which switch will turn off exactly two light bulbs?

F switch 1G switch 2H switch 3I switch 4

3. If only switches 2 and 3 are open, which of the following will happen?

A All three bulbs will remain lit.B Only bulb 1 will remain lit.C Only bulb 3 will remain lit.D All three bulbs will turn off.

4. Which of the following statements is false?

F Bulb 2 will be off when bulb 1 is off.G Bulb 3 will be on if any other bulb is on.H Bulbs 1 and 3 can be on when bulb 2 is off.I Bulb 3 can be on when bulbs 1 and 2

are off.

1. Look at triangle ABC. If you want to draw square ADBC, what would the coordinates ofD be?

A (1, 5)B (3, 3)C (5, 5)D (5, 1)

2. The equation voltage � current � resistance is often called Ohm’s law. If the current in an object is 0.5 A and the voltage across the object is 12 V, what is the resistance of the object?

F 0.042 ΩG 6 ΩH 12.5 ΩI 24 Ω

3. Heather has six large dogs. In one day, each of the dogs eats 2.1 kg of dog food. Which is the best estimate of the total number of kilograms of food all of the dogs eat in 4 weeks?

A less than 150 kgB between 150 and 225 kgC between 225 and 300 kgD more than 300 kg

Use the diagram below to answer the ques-tions that follow.

Read each question below, and choose the best answer.

INTERPRETING GRAPHICS MATH

Switch 2

Switch 1

Switch 3Switch 4

Battery

Bulb 1

Bulb 2Bulb 3

00

1

2

3

4

5

6

1 2 3 4 5 6

A

BCx

y

Chapter 17 • Standardized Test Preparation 505

INTERPRETING GRAPHICS1. A2. H3. C4. F

Question 2: Opening switch 3 is the only way to turn off exactly two light bulbs with a single switch. Opening switch 4 will turn off three light bulbs. Students who select switch 4 might not have read the question carefully enough and might not have noticed the need for exactly two light bulbs. Opening either switch 1 or switch 2 will turn off only one light bulb.

MATH1. C2. I3. D

Question 2: The correct answer is calculated by dividing voltage by cur-rent, or 12 V/0.5 A. Students who select F divided current by voltage, or 0.5 A/12 V. Students who select G mul-tiplied the numbers given. Students who select H added the numbers given.

CHAPTER RESOURCES


CRF • Standardized Test Preparation g

State Resources

For specifi c resources for your state, visit go.hrw.com and type in the keyword HSMSTR.

Sciencein Action

in Action

Language ArtsImagine that you are a hunter living in about 5000 BCE. On a

hunt, you see a sprite as described above. Write a two-page short story explaining what you saw, what your reaction was, and why you think the sprite happened.

MathThe battery in a car provides 12 V. How many times more voltage can a fully grown eel provide than can a car battery? If the voltage provided by the eel were used in a circuit that had a resistance of 200 , what would the current in the circuit be?

Weird ScienceElectric EelsElectric eels are freshwater fish from Cen-tral and South America. They can producepowerful jolts of electrical energy. Electric discharges from eels are strong enough to stun or kill smaller fish and frogs in the water. The eels then swallow their motion-less prey whole. Early travelers to the Ama-zon River basin wrote that in shallow pools, the eels’ discharges could knock horses and humans over. Within the body of an eel, which is 2.5 m long, are a series of electro-plates, or modified muscle tissues that gen-erate low voltages. An eel has 5,000 to 6,000 connected electroplates. In lab experiments, the bursts of voltage from a fully grown eel have been measured to be about 600 V.

Scientific DiscoveriesSprites and ElvesImagine that you are in a plane on a moon-less night. You notice a thunderstorm 80 km away and see lightning move between the clouds and the Earth. Then, suddenly, a ghostly red glow stretches many kilometers above the clouds! You did not expect that!

In 1989, scientists captured the first image of this strange, red, glowing light-ning. Since then, photographs from space shuttles, airplanes, telescopes, and observers on the ground have shown several types of electrical glows. Two were named sprites and elves because, like the mythical creatures, they disappear just as the eye begins to see them. Sprites and elves last only a few thou-sandths of a second.

WRITINGSKILL


Answer to Math Activity

50 times more voltage; I � V/R � 600 V/200 � 3 A

Weird Science

BackgroundOther kinds of electric fish are the electric catfish, found in the larger rivers of tropical Africa, and the torpedo ray, found in warm deep-sea water close to the shore. Members of a species of torpedo ray that lives in the Atlantic Ocean can have a mass up to 90 kg!

Scientific Discoveries

BackgroundThis feature highlights the inter-disciplinary nature of current scientific investigations. Earth scientists, geophysicists, atmo-spheric scientists, astronomers, pilots, and astronauts are all contributing to the research. Researchers are studying diverse aspects of these phenomena, including causes and possible effects. For example, researchers might investigate the impact of these events on atmospheric chemistry. Students may need additional background on the layers of the atmosphere and their characteristics to under-stand the relationship between electrical events and atmo-spheric science.

Answer to Language Arts Activity

Students’ stories should describe the red glow of the sprite and will most likely attribute the sprite as an omen.

Social Studies

Imagine that you are helping run a job fair at your school. Research the requirements for becoming an electrician. Make a brochure that tells what an electrician does and what training is needed. Describe how much the training and basic equipment to get started will cost. Include the starting salary and information about any testing or certifica-tion that is needed.

Pete PerezElectrician Sometimes, you forget just how much of daily life is dependent on electricity—until the electricity goes out! Then, you call an electrician, such as Pete Perez. Perez has been installing electrical systems and solving electricity problems in commercial and residential settings since 1971. “I’m in this work because of the chal-lenge. Everywhere you go it’s something new.”

An electrician performs a wide variety of jobs that may include repairs, routine maintenance, or disaster prevention. One day, he or she might install wiring in a new house. The next day, he or she might replace wiring in an older house. Jobs can be as simple as replacing a fuse or as complicated as restoring an industrial machine. Also, electricians may work under many different conditions, including in a dark basement or at the top of an electrical tower. Perez’s advice to aspiring young electricians is, “Open up your mind.” You never know what kind of job is waiting for you around the corner, because every day brings stranger and more interesting challenges.

To learn more about these Science in Action topics, visitgo.hrw.com and type in thekeyword HP5ELEF.

Check out Current Science®

articles related to this chapter by visiting go.hrw.com. Just type in the keyword HP5CS17.

Chapter 17 • Science in Action 507

Careers

Teaching Strategy--

Tell students that they are most likely to observe sprites and elves while they are watching storms more than 150 km wide with many cloud-to-ground lightning strikes. Advise students to look for sprites at a height 4 to 5 times that of the cloud tops. Because of the nature of night vision, students are most likely to observe sprites out of the corners of their eyes. The actual color of a sprite is pinkish orange, but because of the low light level, students might see the color as green, orange, or white. A hazy or polluted atmo-sphere will make observing these phenomena more difficult.

BackgroundIn the year 2000, the median wage for an electrician was $19.29 per hour. Some earned as much as $31.71 per hour or more. Electricians can often charge more for emergency or late-night jobs. Perez has received calls at 1 A.M. and has worked on some jobs overnight until as late as 7 A.M.

Answer to Social Studies Activity

Students’ brochures should provide accurate information for electrician tools and training in their area. Salaries will vary.

hst physical science teachers edition · osp lesson plans(also in print) trbellringer transparency*...

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