Charging Ahead - An Itroduction to Electromagnetism Malestrom

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A n I n t ro d u c t i o nt o E l e c t ro m a g n e t i s mBy Larry E. Schafer

Featuring sci LINKS©óa new way of connecting text andthe Internet. Up-to-the-minute online content, classroomideas, and other materials are just a click away.

Go to page xiii to learn more about this educational resource.

Arlington, Virginia



Shirley Watt Ireton, Director

Beth Daniels, Managing Editor

Judy Cusick, Associate Editor

Jessica Green, Assistant Editor

Linda Olliver, Cover Design

Art and Design

Linda Olliver, Director

NSTA WebTim Weber, Webmaster

Periodicals Publishing

Shelley Carey, Director

Printing and Production

Catherine Lorrain-Hale, Director

Publications Operations

Erin Miller, Manager

sciLINKS

Tyson Brown, Manager

National Science Teachers Association

Gerald F. Wheeler, Executive Director

David Beacom, Publisher

NSTA Press, NSTA Journals,

and the NSTA website deliver

high-quality resources for

science educators.

Charging Ahead: An Introduction to Electromagnetism

NSTA Stock Number: PB155X

ISBN 0-87355-188-5

Library of Congress Card Number: 2001086220

Printed in the USA by FRY COMMUNICATIONS, INC.

Printed on recycled paper

Copyright © 2001 by the National Science Teachers Association.

The mission of the National Science Teachers Assocation is to promote

excellence and innovation in science teaching and learning for all.

Permission is granted in advance for reproduction for purpose of classroom

or workshop instruction. To request permission for other uses, sendspecific requests to:

NSTA Press

1840 Wilson Boulevard

Arlington, Virginia 22201-3000

www.nsta.org

http://www.nsta.org/

http://www.nsta.org/



Acknowledgments .......................................................................................................... iv

Overview .......................................................................................................................... v

A Learning Map on Electricity and Magnetism ........................................................ viii

Guide to Relevant National Science Education Content Standards ..................... xii

sciLINKS ........................................................................................................................... xiii

A c t i v i t y l : A B o n us f ro m E l e c t r i c a l F l o w — M a g n e t i s m

Student Worksheet........................................................................................................ 1

Teacher’s Guide to Activity 1 ..................................................................................... 9

A c t i v i t y 2 : C o i l s a n d E l e c tro m a g n e t s



A c t i v i t y 3 : M a k i n g a n E l e c t r i c M o t o r —E l e c t ro m a g n e t i s m i n A c t i o n



A c t i v i t y 4 : M o t i o n , M a g n e t i s m , a n d t h e P ro d u c t i o n o f

E l e c t r i c i t y



G l o s s a r y ..................................................................................................................... 65

Contents



NATIONAL SCIENCE TEACHERS ASSOCIATIONiv

Acknowledgments

Larry E. Schafer, the author of Charging Ahead: An Introduction to Electromagnet-ism, teaches physical science and elementary science methods courses at Syracuse

University, where he has also chaired teaching and leadership programs. His previ-

ous work for the National Science Teachers Association (NSTA) was the student-

activity book Taking Charge: An Introduction to Electricity (1992, 2000). He has

directed many funded projects designed to help teachers improve the science edu-

cation in their schools, has worked with the New York State Education Department

to create a statewide system of elementary science mentors, and has co-authored

books for middle school science teachers and their students.

The book’s reviewers were Chris Emery, a physics teacher at Amherst Regional

High School, Amherst, Massachusetts; Dale Rosene, a science teacher at MarshallMiddle School in Marshall, Michigan; Daryl Taylor, a physics teacher at

Williamstown High School in Williamstown, New Jersey; and Ted Willard, senior

program associate at the American Association for the Advancement of Science’s

Project 2061.

The activities in the book were field-tested by Mark M. Buesing and Suzanne

Torrence, both physics teachers at Libertyville High School, Libertyville, Illinois,

and Jay Zimmerman, a physics teacher at Brookfield Center High School, Brookfield,

Wisconsin.

The book’s figures were created by Kim Alberto, Linda Olliver, and Tracey Shipley,

from originals by Larry Schafer.

The NSTA project editors for Charging Ahead: An Introduction to Electromagnet-

ism were Judy Cusick and Anne Early. Linda Olliver designed the book and the

cover. Catherine Lorrain-Hale coordinated production and printing of the book.



CHARGING AHEAD: AN INTRODUCTION TO ELECTROMAGNETISM

Overview

Charging Ahead: An Introduction to Electromagnetism is a set ofhands-on activities designed to help teachers introduce

middle-level and general high school students to electro-magnetism, one of the most fascinating and life-changingphenomenon humankind has witnessed. In 1820, Hans Chris-

tian Oersted, a Danish physicist and schoolteacher, discovered that an elec-trical current produces magnetism. Little did he know that his discoverywould have an impact on modern day lives in profound ways: that electri-cal motors would start cars, turn CDs and disk drives, run can openers,food processors, refrigerators, and clocks, operate pumps for maintaininglife support, and run nearly all of the machines that produce and manufac-ture the many goods upon which we rely. Little did he know that this con-nection between electricity and magnetism would lead others (Michael Fara-

day and Joseph Henry) to discover ways of creating electricity from motionand magnetism and in so doing make it possible for human beings the worldover to move about, heat and light their environments, and instantly andconveniently communicate.

Charging Ahead uses readily available materials to introduce studentsto electromagnetism, to the factors that determine the magnetic strength ofelectrical coils, to the application of electromagnetism in the construction ofan electrical motor, and to the production of electricity through the con-struction of a generator. Throughout Charging Ahead, students are introducedto historical perspectives and to technological applications (circuit break-ers, mag-lev trains, superconducting generators, etc.) of electromagnetism.

F i t t i n g Charging Ahead i n t o Yo u r C u r r i c u l u m

Charging Ahead is a companion guide to NSTA’s Taking Charge: An Intro-duction to Electricity. While students would benefit from experiencing theactivities in Taking Charge, it is not necessary that students complete TakingCharge before attempting the activities in this book. Students will neverthe-less need a basic understanding of electrical circuits to understand the ideaspresented in Charging Ahead.

Topic: electromagnetism

Go To: www.scilinks.org

Code: CH001

Topic: Hans Christian

Oersted


Code: CH002

http://www.scilinks.org/






NATIONAL SCIENCE TEACHERS ASSOCIATIONvi

Key relationships are developed from what students experience in the

activities. Abstract formulations and mathematical descriptions, althoughimportant, are minimized in Charging Ahead. The activities therefore serveas “end points” for middle school students and “starting points” for highschool students who are on the path toward understanding abstract formu-lations of electromagnetism and electromagnetic induction.

Charging Ahead addresses the National Science Education Standards in anumber of ways. Students learn about energy forms and energy transfer,engineering design and troubleshooting, and science-technology relation-ships. Students are challenged to solve problems and to think critically andcreatively. See p. xii for a Guide to Relevant National Science EducationContent Standards.

O rg a n i z a t i o n

The activities in Charging Ahead use an inquiry approach to guide stu-dent understanding of the concept goals. Each student activity includes anintroduction, a description of the materials needed, a statement of whatstudents will learn, and procedures to follow. None of the activities require“high tech” equipment. Wires, flashlight batteries and bulbs, magnets, andmagnetic compasses are the basic materials used in the activities.

The procedure section of each activity is designed so that students canperform the activity without the teacher’s constant involvement and direc-tion. The procedure section presents students with problems to solve, ques-

tions to answer, and tasks to accomplish. It should be clear that studentswill occasionally face difficulty as they work through the procedures. Un-derlying the design of these activities is the idea that students will moremeaningfully understand the concepts and relationships if they are chal-lenged to figure some things out for themselves.

Each activity is accompanied by a teacher’s guide to the activity. Theguide is written so that the teacher acquires a brief overview of what willhappen in the activity, directions for the construction of equipment and/orthe selection of materials, time management recommendations, cautionarynotes, ideas for extended activities, and answers to questions.

A s s e s s m e n t M e t h o d sThe teacher can use both formative and summative assessment with Charg-

ing Ahead. The answers that students give to the questions in each activity pro-vide a formative record of their thinking and learning—showing students andthe teacher what students understand, what is still fuzzy or missing, andwhether students can now use what they know. The suggestions for furtherstudy at the end of each activity can be used to extend—and then test—stu-



vCHARGING AHEAD: AN INTRODUCTION TO ELECTROMAGNETISM

dents’ learning. These extensions are authentic applications of the concepts

students have just investigated. You may wish to build an assessment rubricfor one or more of the extensions and use it as a summative assessment of yourstudents’ mastery of electromagnetism concepts.

S p e c i a l C o n s i d e r a t i o n s

The first and second activities are fairly straightforward. They call onstudents to examine the relationship between electrical flow and magnetismand investigate how to increase the magnetic forces created by a current-carrying wire. The third and fourth activities challenge students to build anelectric motor and an electric generator. Electrical motors and generators builtfrom readily available materials are somewhat temperamental. While each

design has been thoroughly tested (75 percent of sixth graders had an electri-cal motor going in 30 minutes), neither students nor teachers should expectsuccess without some “troubleshooting.” Success can be greatly improved byusing the recommended materials and by carefully following the directionsand suggestions. The need to “troubleshoot” to get things to work should betaken as an opportunity to help students value the creative and persistentwork done by engineers who design and debug the devices that reliably work.

Initial construction of motor and generator parts will take some time.Students can help with the construction of those parts. Once the parts areconstructed, they can be used repeatedly by different classes of students.

As a consequence of taking part in electricity activities, some students

may become very interested in motors, generators, and other electrical de-vices. They may be inclined to examine these devices on their own in back-yards and basements. The investigation of household electrical devices canlead to serious injury. Therefore, please warn students that they should notinvestigate electrical devices without the help and supervision of a knowl-edgeable adult.

The activities in Charging Ahead are safe since small currents and volt-ages are used. Short circuits are sometimes used in the activities and thesecircuits can produce hot wires. Student should be warned to keep shortcircuits on only for short periods of time (a few seconds). In such shortperiods of time, the wires wil not significantly heat up nor will batteries

quickly wear out.The four Charging Ahead activities build on each other, connecting sci-ence content as described in the Atlas of Science Literacy map on p. xi. Youcan compare the concept goals at the start of each activity with your owninstructional goals to determine which activity to use.



NATIONAL SCIENCE TEACHERS ASSOCIATIONviii

W h a t I s T h i s M a p ?

The map on page xi is a way of considering and organizing sciencecontent standards. The map uses the learning goals (or parts of them) of theAmerican Association for the Advancement of Science’s Science for All Ameri-cans (1989) and Benchmarks for Science Literacy (1993). Content standards fromthe National Science Education Standards (NSES) (National Research Council1996) overlap nearly completely with those goals. Arrows connecting thegoals imply that understanding one goal contributes to the understandingof another. Goals that deal with the same idea are organized into vertical

“strands,” with more sophisticated goals above simpler ones. Descriptivelabels for the strands appear at the bottom of the map.The science content on the map lists the ideas relevant to students’ un-

derstanding of electricity and magnetism that are both important and learn-able. Your students may well learn more, but will learn better after the basicscience literacy described on the map has been achieved. This map tracesthe ideal development of electricity and magnetism knowledge from kin-dergarten to twelfth grade. Horizontal lines represent the level of gradeappropriateness.

Charging Ahead provides instructional methods that primarily achievelearning goals for the map strand labeled “electromagnetic interactions.”The map suggests what ideas students must have before trying to examinethe relationship between electricity and magnetism. Unit activities as pre-sented may not be sufficient for students to become proficient with some ofthe basic or extended ideas in the map strand; checking the progress of yourstudents along the way will help you see how to adapt instruction. Unitactivities may also touch on concepts outside of what the various sciencestandards consider essential for basic science literacy. Therefore, you maydecide to focus activities to make sure your core learning goals are achieved.

A Learning Mapon Electricity andMagnetism




H o w C a n I U s e t h e M a p ?

An Atlas map is designed to help clarify the context of the benchmarkor standard: where it comes from, where it leads, and how it relates to otherstandards. With the map as a guide, you can make sure your students haveexperience with the prerequisite learning, and you can actively draw stu-dents’ attention to related content—getting their framework for learningready!

In addition to using the map to plan instruction, you may wish to an-notate the map with common student misconceptions to address or com-mon accurate conceptions that you can invoke to dispel these misconcep-tions. Motivating questions that have worked for you, and phenomena toillustrate points, may also find a place on your annotated map.

The map can help you connect your instruction to your state sciencestandards. As of this writing, 49 of the 50 states in the United States havedeveloped their own standards, most modeled directly on the National Sci-ence Education Standards or the Benchmarks for Science Literacy. The correla-tion between the NSES and Benchmarks in science content is nearly 100 per-cent. So there is a unity of purpose and direction, if not quite a commonlanguage. Fortunately, the National Science Foundation, the Council of ChiefState School Officers, and other groups have funded and developed websitesto guide educators in correlating these national standards with their stategoals (e.g., the ExplorAsource website at www.explorasource.com/educator. Thewebsites of many state departments of education also provide this correla-

tion service for educators.The map can also provide a way to think about the design of studentassessment . The goal of your summative assessment is to determine whetherstudents can apply their learning to new situations—to show you, and toshow themselves, that they have a new tool for understanding.

A re T h e re O t h e r M a p s ?

These maps are being copublished by AAAS and NSTA in a new two-volume work, Atlas of Science Literacy . The complete Atlas will contain nearly100 similar maps on the major elementary and secondary basic science top-ics: gravity, cell functions, laws of motion, chemical reactions, ratios and

proportionality, and more.The connected learning goals displayed in Charging Ahead are only part

of a map that is—at the time of this printing—subject to revision. As addi-tional maps are developed and tested, they will be linked to the Charging

Ahead page on the NSTA website and added to successive editions of Charg-ing Ahead.

http://www.explorasource.com/educator





NATIONAL SCIENCE TEACHERS ASSOCIATIONx

M a p , A s s e s s m e n t , a n d t h e C o n s t r u c t i v i s t

P ro c e s sUse the map as an aid to your constructivist teaching methods, allow-

ing students to recognize and integrate concepts—either those never learnedor those incompletely remembered—into the big picture of why these con-cepts are useful to know.

Before you undertake any of the four activities in this book, it is impor-tant to know whether your students have mastered the principles in themap that lead to their current grade level. You may, for example, be sur-prised to learn that some of your high school juniors do not really under-stand that “magnets can be used to make some things move without beingtouched,” a concept that, according to the strand map, should be mastered

by grade three. Students may also have a mix of true and false understand-ings about electricity and magnetism as they begin the Charging Ahead ac-tivities. It may be wise to ascertain—perhaps by having each student do a“web” of everything he or she can think of about the term “magnetism”and reviewing those webs—to ensure that all students are starting with the

basic information they need to build on in order to understand the conceptspresented in these activities.



Grades 6-8

Grades 3-5

Grades K-2

Moving electric charges

produce magnetic forces

and moving magnets

produce electric forces.

4G/H5

The interplay of electric

and magnetic forces is the

basis for electric motors,

generators, and many

other modern

technologies, including the

production of

electromagnetic waves.

4G/H5

Different kinds of materials

respond differently to

electric forces. In

conducting materials such

as metals, electric charges

flow easily, whereas in

insulating materials, such

as glass, they can move

hardly at all. 4G/H4

Vibrating electric charges

produce electromagnetic

waves around them.

4F/H3

Negative charges, being

associated with electrons,

are far more mobile in

materials than positive

charges are. 4G/H3

Electricity is used to

distribute energy quickly

and conveniently to

distant locations. 8C/M4

There are two kinds of

charges—positive and

negative. Like charges

repel one another,

opposite charges attract.

4G/H3

Without touching them, a

magnet pulls on all things

made of iron and either

pushes or pulls on other

magnets. 4G/E2

Magnets can be used to

make some things move

without being touched.

4G/P2

Electric currents and

magnets can exert a force

on each other. 4G/M3

Electric currents circulating

in the Earth’s core give the

Earth an extensive

magnetic field, which we

detect from the orientation

of our compass needles.

SFAA p.56

Electric ChargesStrand

Electric CurrentsStrand

ElectromagneticInteractions Strand

Magnets Strand

ELECTROMAGNETISM

This map was adapted from Atlas of Science Literacy (AAAS 2001). For more information, or to order, go to www.nsta.org/store.

Map Key

Codes(e.g.,

4G/45)

SFAA

chapter, section,and number ofcorrespondinggoal fromBenchmarks for Science Literacy (AAAS 1993)

concept fromScience for All Americans (AAAS 1989)

Grades 9-12

http://www.nsta.org/store

http://www.nsta.org/store



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Charging Ahead: An Introduction to Electromagnetism brings you sciLINKS, a new project that blendsthe two main delivery systems for curriculum—books and telecommunications—into a dynamicnew educational tool for children, their parents, and their teachers. sciLINKS links specific sciencecontent with instructionally rich Internet resources. sciLINKS represents an enormous opportu-nity to create new pathways for learners, new opportunities for professional growth among teach-ers, and new modes of engagement for parents.

In this sciLINKed text, you will find an icon near several of the concepts you are studying.Under it, you will find the sciLINKS URL (www.scilinks.org) and a code. Go to the sciLINKS web-site, sign in, type the code from your text, and you will receive a list of URLs that are selected byscience educators. Sites are chosen for accurate and age-appropriate content and good pedagogy.The underlying database changes constantly, eliminating dead or revised sites or simply replacingthem with better selections. sciLINKS also ensures that the online content teachers count on re-mains available for the life of this text. The sciLINKS search team regularly reviews the materialsto which this text points—revising the URLs as needed or replacing webpages that have disap-peared with new pages. When you send your students to sciLINKS to use a code from this text,you can always count on good content being available.

The selection process involves four review stages:

1 A cadre of undergraduate science education majors searches the World Wide Web forinteresting science resources. The undergraduates submit about 500 sites a week forconsideration.

2 Packets of these webpages are organized and sent to teacher-webwatchers with ex-pertise in given fields and grade levels. The teacher-webwatchers can also submitwebpages that they have found on their own. The teachers pick the jewels from thisselection and correlate them to the National Science Education Standards. These pagesare submitted to the sciLINKS database.

3Scientists review these correlated sites for accuracy.

4 NSTA staff approve the webpages and edit the information for accuracy and consis-tent style.

sciLINKS is a free service for textbook and supplemental resource users, but obviously some-one must pay for it. Participating publishers pay a fee to NSTA for each book that contains sciLINKS.The program is also supported by a grant from the National Aeronautics and Space Administra-tion (NASA).

xCHARGING AHEAD: AN INTRODUCTION TO ELECTROMAGNETISM






NATIONAL SCIENCE TEACHERS ASSOCIATIONxiv




B a c k g ro u n d

When you create a closed circuit with a battery, electrons flow throughthe wires, the bulb lights up and gets hot, and the wires and battery warmup. Besides the chemical reactions going on inside the battery, is anythingelse happening? It is hard to tell unless you can use some detection device.In this investigation, you will use a compass to detect magnetism. You willuse the compass to investigate the relationship between electrical flow and

any magnetism that is produced from that flow.

C o n c e p t G o a l s

■ A current-carrying wire produces a magnetic effect (deflects a compassneedle) in the region around the wire. That magnetic effect is calledelectromagnetism.

■ Electrons move along a wire from the negative end of the battery to thepositive end of the battery.

■ The direction of the electron flow in a wire determines the direction ofthe magnetic field around the wire.

■ The strength of the magnetic influence (field) around a wire becomes lessat greater distances from the wire.

■ Magnetic fields (regions of magnetic influence) have direction and“strength.”

■ The direction of the magnetic field at a particular point in space is thedirection a compass needle would point if the compass were located atthat point.

A c t i v i t y 1

S t u d e n t W o r k s h e e t

A Bonus from

Electrical Flow —Magnetism

Topic: electrical circuit

Go To: www.scilinks.org Code: CH003

Topic: magnetic effect


Code: CH004







NATIONAL SCIENCE TEACHERS ASSOCIATION2

■ A left hand is an effective model for showing the relationship between

the direction of the magnetic field and the direction of electron flow.

P ro c e d u re

1 If you have not used a compass recently, you may want to refreshyour memory. The colored or pointed end of the needle usually pointsapproximately toward the Earth’s geographic north. Hold the compassout in front of you, away from any metal objects, and note that the coloredor pointed end of the needle always points in the same direction, evenwhen you rotate the base or case of the compass.

Move your compass close to an iron or steel object and notice that thecompass needle is attracted to the object. It is important, therefore, to keepthe compass away from iron or steel objects when you are using it to detectmagnetism from other objects. Iron or steel under the desktops can influ-ence the direction in which the compass needle points.

The compass needle is nothing more than a small, light magnet thateasily spins about its center when it interacts with other magnets. Thecompass needle is attracted to iron and steel objects because the needleitself causes those objects to become temporarily magnetized.

2 In 1820, Hans Christian Oersted, a Danish physicist and schoolteacher,made the observation you are about to make. His discovery set the stage forthe development of many modern conveniences, including electrical mo-

Compass

Wire on top of compass

Needle position when wireis not connectedto battery

Battery

F i g u re 1 . 1

M a t e r i a l s

For each group:■ one “D” battery (dry

cell) and one battery

holder

■ one directional,

magnetic compass

with a needle that is

free to move easily

without sticking

■ one 60-cm piece of

#24 enamel-coated

(insulated) wire (with sanded ends) or #22

plastic-coated wire

(with stripped ends)

tors and the generation of electricityfrom motion.

a Place the compass on the table atleast 15 cm away from the bat-tery. Connect one end of the wireto the battery. Place the wire in astraight line directly over thecompass and in line with the

needle. Briefly touch (no morethan two seconds) the other endof the wire to the battery and ob-serve what happens to the com-pass needle.

Draw an arrow on the com-pass illustration in Figure 1.1 toshow the direction of the needle




Compass

Wire beneath compass

Needle position when wireis not connectedto battery

Battery

when a current-carrying wire is

on top of the compass. Thepointed end of the arrow repre-sents the “north-seeking” end ofthe needle. Also draw an arrowon the wire showing the directionin which the electrons are mov-ing in the wire. Recall that elec-trons move along a wire from thenegative end of the battery to thepositive end of the battery.

b Repeat the above activity, but this

time place the wire under thecompass and align the wire withthe compass needle. Draw an ar-row on the compass drawing(Figure 1.2) to record the direc-tion of the needle when a current-carrying wire is under the compass. Also, draw an arrow showing thedirection of electron flow in the wire. Remember to keep the electricityflowing in the wire for only two seconds.

c Note the direction in which the needle moved (“deflected”) in 2b above.

With the wire under the compass and without changing the positions ofthe compass or the wire, what can you do to make the deflected needlepoint in the opposite direction? Describe your solution in the space

below.

d It should be clear that a current-carrying wire is somehow creating amagnetic influence in the space around it. What can you do to find out

how the “strength” of that influence changes with different distancesfrom the wire? Describe your solution, your conclusion about distanceand “strength,” and how your observations support your conclusion.

F i g u re 1 . 2




e A magnetic field is a region of space in which there is a magnetic influ-ence. There is a magnetic field in the space around a magnet. A compasscan detect a magnetic field if the field is strong enough. Because thecompass needle is deflected in the region around the current-carryingwire, you can conclude that there is_____________________________________________________________________around a current-carryingwire.

f Magnetic fields have both “strength” and direction at each point in space.The direction is the direction that a compass will point if it is held at thatpoint in space. The magnetic field both above and below a current-carry-ing wire is: (circle 1 or 2)

1 in line with the wire.

2 across the wire.

g To change the direction of the magnetic field above a wire, you wouldhave to change the __________________ of the electron flow in the wire.Without moving the wire above the compass, you can do this by

______________________________________________________.

h The magnetic field around a current-carrying wire is “stronger”: (circle1 or 2)

1 closer to the wire.

2 farther away from the wire.

3 You can use your left hand as a model of the relationship between thedirection of the electron flow and the direction of the magnetic field (thedirection the compass would point) created by that flow.




A L e f t - h a n d M o d e l

Pretend to grasp the wire with your left hand. Wrap your fingers aroundthe imaginary wire in such a way that your left thumb points in the direc-tion of electron flow (Figure 1.3). Your fingers will then wrap around thewire in the direction of the magnetic field. You can rotate your hand aroundthe wire to see which way your fingers point at any position around thewire (Figure 1.4).

Practice using the left-hand model by answering the following ques-tions associated with Figure 1.5. (circle the correct answer)

a The magnetic field directly above the wire at “a” would point:

1 to the left.

2 to the right.

3 straight up out of the page.

4 straight down into the page.

Direction of

magnetic field

Direction ofelectron flow

Left hand

F i g u re 1 . 3




b The magnetic field directly belowthe wire at “b” would point:

1 to the left.

2 to the right.



c The magnetic field directly to theleft of the wire (neither above nor

below the wire) at “c” wouldpoint:

1 to the left.

2 to the right.



Wire

Field below wire?

Field above wire?

Field to theright of wire?

Field to theleft of wire?

b

c d

Electron flow in wire

a

F i g u re 1 . 5

Direction ofelectron flow

Direction of magnetic field

Left hand

F i g u re 1 . 4




Compasses

End of wire

coming out of

page; electrons flowalong wire, up

and out of pageCompasses

F i g u re 1 . 6d The magnetic field directly to the

right of the wire (neither abovenor below the wire) at “d” wouldpoint:

1 to the left.

2 to the right.



e Observe Figure 1.6 and assume

that the dot in the center is theend of a wire that is coming outof the page. Further assume thatelectrons are flowing along thatwire out of the page directly up-ward from the page. Use yourleft-hand model to determine thedirection of the compass needle(direction of the magnetic field) at each of the compass points aroundthe wire. Draw the compass needles in the four compasses and use thepointed head of the arrow as the “north-seeking” end of the compass

needle.




C a u t i o n

Short circuits are

created when the

wire is connected to

the ends of the bat-

tery. The short circuit

will heat up the wire

and quickly wear

down the battery.

Caution the students

to maintain a short

circuit for only a

couple of seconds at

a time. They can do

this by connecting

one end of the wire

to the battery and

briefly touching the

other end of the wire

to the battery.

T e a c h e r ’ s G u i d e T o

A c t i v i t y 1

A Bonus from

Electrical Flow —Magnetism

W h a t i s h a p p e n i n g ?

In this activity, students dis-cover that a current-carrying wireproduces a magnetic field around it.

They use a compass to detect thismagnetic field, and they observethat the direction of the field isacross the direction of the electronflow. Furthermore, the studentslearn that the field is “stronger”closer to the wire. In addition, thestudents learn that the direction ofthe magnetic field at a point in spaceis described as the direction thenorth-seeking end of a compass

would point. Students can use theirleft hands to model the relationship between the direction of the electronflow and the direction of the mag-netic field it produces. Studentspractice applying the model to dif-ferent examples.

T i m e m a n a g e m e n t

One class period (40–60 minutes)should be enough time to completethe activity and discuss the results.

P re p a r a t i o n

Collect the materials listed onpage 2. Make sure that the batteriesare not dead, that the compasseswork, and that the ends of the wiresare stripped (plastic-coated wire) orsanded (enamel-coated wire). If thestudents have not worked withenamel-coated wire, show them howto use sand paper to sand off theenamel from the ends of the wires.

Students may find that their com-passes point in different directionswithout any current-carrying wires ormagnetic materials nearby. Why don’tall the compasses point north? Whydo the compasses point in different




Wire on top ofcompass

Drawn

needle

Electron flow

Electron flow

Compass

Battery

F i g u re 1 . 7

directions when they are moved

around on the desks or in the room?Often the iron or steel in desks, filingcabinets, walls, etc. influences the di-rection of the compasses. For an ac-curate “north reading,” a compassmust be away from all iron and steelobjects.

S u g g e s t i o n s f o r f u rt h e rs t u d y

Challenge groups to get together

to see what happens when two cur-rent-carrying wires are held in linewith a compass needle. Studentsshould discover that when bothwires carry electrons in the same di-rection over and in line with a com-pass needle, the needle deflection isgreater than when just one wire isused. Students also should discover

that when the wires carry electrons

in opposite directions over and in linewith the compass needle, the needledeflection is less because the mag-netic fields exert forces on the needlein opposite directions.

Students have studied direct cur-rent electricity where the electronsmove in one direction in the conduc-tor. Alternating current electricity isused in our homes. The electrons inthe alternating currents switch direc-tions 60 times each second. If this elec-tron jiggling is going on in the wiresin our homes, what is happening tothe magnetic field surrounding thosewires? Have students consider thisquestion and guide them to under-stand that the magnetic field aroundthe wires in our homes must be jig-gling or changing directions 60 timeseach second. When held near a cur-rent-carrying house wire, a typicalcompass needle does not show deflec-

tion. The inertia of the needle preventsthe needle from changing directions60 times each second. Just as theneedle begins to move in one direc-tion, it is forced in the opposite direc-tion.

Answers to questions found within

Procedure on pages 2–7.

2a. Draw an arrow on the compass in

Figure 1.1 to show the direction of the needle when a current-carryingwire is on top of the compass. Alsodraw an arrow showing the directionof electron flow in the wire.

One answer is shown in Figure1.7. If the terminals of the battery




F i g u re 1 . 8

wire and compass are closer. As-suming that more deflection

means a “stronger” interaction,the conclusion is that the mag-netic influence is “stronger”closer to the wire.

2e. When a compass needle is deflectedin the region around a current-car-rying wire, you can conclude thatthere is a magnetic field around thewire.

2f. The magnetic field both above and

below a current-carrying wire is: (1)in line with the wire or (2) across thewire?

(2) across the wire.

2g. To change the direction of themagnetic field above a wire, youwould have to change the direction

Compass

Electron flow

Electron flow

Drawnneedle

Wire beneathcompass

Battery

were reversed, the drawn arrow

would be deflected to the otherside of the wire.

2b. Draw an arrow on the compass inFigure 1.2 to record the direction of the needle when a current-carryingwire is under the compass. Also,draw an arrow showing the directionof electron flow in the wire.

One answer is shown in Figure1.8. If the terminals of the battery

were reversed, the drawn arrowwould be deflected to the otherside of the wire.

2c. Note the direction in which the needlemoved (“deflected”) in 2b above. Withthe wire under the compass and with-out changing the positions of the com-

pass or the wire, what can you do tomake the deflected needle point in theopposite direction?

The solution is to keep the wiresand compass the same, butswitch wires on the terminals ofthe battery. This sends the elec-trons in the opposite directionthrough the wire.

2d. What can you do to find out how the“strength” of the magnetic influencearound the current-carrying wirechanges at different distances fromthe wire? Describe your solution,

your conclusion about distance and“strength,” and how your observa-tions support your conclusion.

Change the distance between thecurrent-carrying wire and com-pass. Note that there is greater de-flection in the compass when the




of the electron flow in the wire. With-

out moving the wire above the compass, you can do this by switching the ends of the wire on the termi-nals of the battery.

2h. The magnetic field around a current-carrying wire is “stronger”: (1)closer to the wire or (2) farther away

from the wire.

(1) closer to the wire.

3a. The magnetic field directly above thewire at “a” would point: (1) to theleft, (2) to the right, (3) straight upout of the page, or (4) straight downinto the page.

(1) to the left.

3b. The magnetic field directly below thewire at “b” would point: (1) to theleft, (2) to the right, (3) straight up

out of the page, or (4) straight down

into the page.(2) to the right.

3c. The magnetic field directly to the leftof the wire (neither above nor belowthe wire) at “c” would point: (1) tothe left, (2) to the right, (3) straightup out of the page, or (4) straightdown into the page.

(4) straight down into the page.

3d. The magnetic field directly to theright of the wire (neither above norbelow the wire) at “d” would point:(1) to the left, (2) to the right, (3)straight up out of the page, or (4)straight down into the page.

(3) straight up out of the page.

3e. Observe Figure 1.6 and assume thatthe dot in the center is the end of awire that is coming out of the page and

that electrons are flowing along thatwire directly upward from the page.Use the left-hand model to determinethe direction of the compass needle ateach of the compass points around thewire. Draw the compass needles in thecompasses; use the pointed head of thearrow as the “north-seeking” end of the compass needle.

The compass directions are

shown in Figure 1.9.

Compasses

Compasses

End of wire

coming out of

page; electrons flowalong wire, up and

out of page

F i g u re 1 . 9

N o t e : The left-hand model is the sameas the right-hand rule found in physicstextbooks. Here, the direction of electron

flow is used. The right-hand rule usescurrent direction (positive charge flow).




A c t i v i t y 2


Coils and

Electromagnets

B a c k g ro u n d

Hans Christian Oersted was probably very excited about his discoverythat a current-carrying wire produces a magnetic effect in the region aroundthat wire. Perhaps he realized that current-carrying wires could produce

very strong magnetism that may be able to exert forces to turn wheelsand accomplish work. All of modern day electric motors depend on theproduction of magnetism from current-carrying wires. In this activity, youwill investigate how to make the magnetism from current-carrying wiresstronger. In the next activity you will use an electromagnet to make an elec-tric motor.


■ A coil of wire that carries a current produces a stronger magnetic fieldthan just a straight wire that carries the same current.

■ A piece of iron (e.g., a nail) placed in a coil that carries a current will become magnetized by the coil.

■ A piece of magnetized iron in a coil that carries a current will produce astronger magnetic field than just the coil alone.

■ An electromagnet is a magnet that is produced by a coil that carries anelectrical current.

Topic: electromagnet


Code: CH005






Briefly touch wire

to battery terminal

Straws

V shapedpaper clip

M a t e r i a l s

For each group:■ one “D” battery (dry

cell) and one battery

holder


enamel-coated

(insulated) wire (with

sanded ends) or bell

wire (with stripped

ends)


enamel-coated

(insulated) wire (with

sanded ends) or bell

wire (with stripped

ends)

■ three plastic drinking

straws

■ two pieces of masking

tape

■ one large, steel paper

clip (4.8 cm x 1 cm)

■ twenty large, steel

paper clips chained

together

■ one steel or iron nail

(8–10 cm long )

■ one beaker, or a foam

or plastic cup

■ one light bulb in its

socket

■ scissors

■ The strength of an electromagnet increases as the number of wraps in the

coil increases.■ The strength of an electromagnet decreases as the electrical current in the

coil decreases.

P ro c e d u re

1 In the last activity, you deflected a compass needle with a current-car-rying wire. Because a current-carrying wire acts like a magnet (it producesa magnetic effect in the region around it), perhaps the wire will attract ironobjects just as a regular permanent magnet does.

a Tape two plastic drinking straws to the bottom of an overturned cup or beaker. The ends of the straws should be about 8 cm apart. Open thelarge paper clip and bend it into a “V” shape as shown below. Place the“V” shaped paper clip on the “arms” of the drinking straws so that iteasily moves back and forth (Figure 2.1).

F i g u re 2 . 1




b Attach one end of the 80-cm wire to one end of the battery. Use your

fingers to stop the paper clip from swinging back and forth. Move thewire very near the bottom part of the “V” (again, see Figure 2.1). Don’ttouch the paper clip. When the wire is very close to the stationary paperclip, briefly touch the other end of the wire to the battery to send a cur-rent through the wire. Is the paper clip attracted to the current-carryingwire? Write your answer below.

c Starting about 8 cm from one end of the wire, wind the wire aroundyour index finger. Be careful not to wind too tightly. Stop winding whenyou are about 8 cm from the other end of the wire and slip the coil ofwire off your finger. Keep the coil together.

Attach one end of the wire to one end of the battery. Again use yourfingers to stop the paper clip from swinging back and forth. Move thecoil very near the bottom part of the “V.” Don’t touch the paper clip.When the coil is very close to the stationary paper clip, briefly touch theother end of the wire to the battery to send a current through the coil. Isthe paper clip attracted to the current-carrying coil? How does the coil’s

attraction compare to the attraction of a single strand of wire? Writeyour answers below.

d Disconnect the wire from the battery and unwrap the coil of wire. Donot pull on the ends of the wire to straighten out the coil; this willproduce a kinky mess.

Next, starting about 8 cm from the end of the wire, wrap the wire arounda drinking straw (Figure 2.2). Try to keep all the coils within a 1-cmsection of the straw. Keep the coil rather tight but do not wrap so tightly

C a u t i o n

A short circuit is

created when the

wire is attached to

the battery. The

wire gets hot. Do

not allow the ends

of the wire to touch

the battery for more

than two seconds

at a time.




that the straw is crushed. Stop wrapping when there are about 8 cm of

wire left. Next, use the scissors to cut one end of the straw close (0.3 cm)to the coil.

Connect one end of the wire toone of the battery terminals. Stopthe “V” from moving. Move thecoil near the end of the bottom ofthe “V.” Briefly touch the otherend of the wire to the otherterminal of the battery to send acurrent through the coil. Describe

below the extent to which the cur-

rent-carrying coil attracts the “V”paper clip.

F i g u re 2 . 2

Briefly touch wire tobattery terminal

Coil aroundend of straw

Next, place the nail into the end of the straw near the coil. Hold the headof the nail near the “V” and briefly send a current through the coil. Howdoes the coil-and-nail’s attraction of the “V” compare to the coil’s at-traction alone? Write your answer below.

2 When you wrap an insulated current-carrying wire around an iron orsteel object, you create an electromagnet. As you found in step 1d above,the iron or steel can greatly increase the magnetic force exerted on nearbyobjects. The magnetism created by the coil turns the nail into a temporarymagnet. For electromagnets to be of any use, they must be able to createrather large magnetic forces. The question arises: How can we increase thestrength of an electromagnet?




Challenge: Use the nail, the bat-

tery, and the chain of 20 paperclips to investigate how the number of coils wrapped around thenail determines the strength ofthe electromagnet (the number ofpaper clips lifted off the table).

Keep the coils near the head ofthe nail.

Stretch out the chain of paperclips on the table.

Use the head of the nail to pickup the first paper clip in thechain. Smoothly move the nail(with the first paper clip at-tached) over the second paperclip and try to pick two paperclips off the table (Figure 2.3).Keep moving down the chain tosee how many paper clips theelectromagnet will pick off the

Three paperclips

lifted off

tabletop

F i g u re 2 . 3

table. Keep the nail vertical and in line with the string of paper clips that

have been picked off the table.

Now wrap some more coils around the nail and follow the same stepsas above.

Conclusion: In the space below, describe the relationship betweenthe number of coils in an electromagnet and the strength of theelectromagnet.




3Construct an electromagnet thatwill consistently pick up at least three

paper clips from a chain of paperclips on the tabletop.

Next, place a light bulb andsocket in the circuit, as shown in Fig-ure 2.4. Use the electromagnet to tryto pick up at least three paper clipsalong the chain.

a Describe below how the bulb inthe circuit with the electromag-

net influenced the strength of theelectromagnet.

F i g u re 2 . 4

Bulb in the circuitwith the electromagnet

b When the bulb was placed in the circuit with the electromagnet, the bulb provided resistance to the flow of electricity and caused the electri-cal flow to be reduced in all parts of the circuit. In other words, the bulbreduced the rate of electrical flow or current through the electromagnet.How does the current (rate of electrical flow) in an electromagnet deter-mine the strength of the electromagnet?




S u m m a r i z e

c List the factors found in this activity that influence the strength of anelectromagnet.

d Describe the relationship between each factor and the strength of theelectromagnet.



2CHARGING AHEAD: AN INTRODUCTION TO ELECTROMAGNETISM


In this activity, students learnthat a current-carrying wire is notonly able to show magnetic effects bydeflecting compass needles, but, likeregular, permanent magnets, it is ableto attract iron and steel objects. Ad-ditionally, students discover thatmagnetic forces increase when thenumber of wraps, coils, or windingsin an electromagnet increases andwhen the current in the coils in-creases.


One or two class periods (40–60minutes each) should be enough timeto complete the activity and discuss

the student responses.


Collect the materials listed onpage 14. Make sure that the ends ofthe wires are sanded or stripped.Also, because the batteries must be


A c t i v i t y 2

Coils andElectromagnets

C a u t i o n

The students will

be creating short

circuits with their

electromagnets and

there is a dangerthat the wires and

battery will get hot.

Remind the stu-

dents to disconnect

their batteries from

the electromagnet

as soon as they

have made an

observation or as

soon as the wirebegins to get warm.

rather “strong” for this activity, the batteries should be checked. If the batteries are weak, it may be neces-sary to provide each group with two

batteries hooked up in series.

S u g g e s t i o n s f o rf u r t h e r s t u d y

Electromagnets are used inmany different places throughout thehome. There are electromagnets inevery electric motor (e.g., disk, CD,and tape drives; can openers; fans;electric toothbrushes; garage dooropeners). Electromagnets also areused in sound speakers (e.g., head-sets, phones, radios).

There are electromagnets that

protect our homes from fires that arecaused by overheated wires in elec-trical systems. The protection devicesare called circuit breakers, and they

break or open circuits when the cur-rent becomes great enough to heatthe wires to dangerous temperatures.Figures 2.5 and 2.6 show the basic




workings of the circuit breaker. The

more current that runs through thecircuit, the stronger the pull of theelectromagnet (e). If the current getstoo high, the electromagnet becomesstrong enough to pull open lever A.This allows lever B to spring back-ward and open the circuit at 1 and 2.To reset the switch, lever B has to bepushed back to where it connectswith lever A and closes the circuit at1 and 2.

Challenge: Have students createtheir own circuit breakers using

batteries, bulbs, wires, nails, tape,paper clips, etc. They can testtheir circuit breakers by shortingaround the bulb in the circuit. Toshort around the bulb, use a 20-cm wire to connect the two ter-minals of the bulb holder(Figure 2.7). The short shouldgreatly increase the current and

the increased current shouldstrengthen the electromagnet thatpulls open the switch and breaksthe circuit.

However, as soon as the circuitis opened, the electromagnetshould stop pulling. Without thepull of the electromagnet, thecircuit may close again. If thecircuit does close again, theelectromagnet will turn on and

reopen the circuit. This circuit,which repeatedly opens andcloses, is the type of circuit foundin doorbell buzzers.

Because it would be unwise to al-low a circuit breaker to close the

Circuit breakerclosed

1 2

e

Iron

AB

To power To power

Spring

To rest of circuit

To rest of circuit

12

e

Iron

AB

To power To power

Spring

Circuit breaker

open

To rest of circuit

To rest of circuit

F i g u re 2 . 6

F i g u re 2 . 5




circuit immediately after

breaking it, the student in-ventors will have to designa way to keep the circuitopen once the electromag-net opens the circuit andturns off the electromagnet.In real circuit breakers, theelectromagnet pulls on atrigger that releases aspring-loaded switch. Thespring holds the switchopen until it is reset.



1b. Attach one end of the 80-cm wire toone end of the battery. Move the wirevery near the bottom part of the “V”of the paper clip. Briefly touch theother end of the wire to the batteryto send a current through the wire.

Is the paper clip attracted to the cur-rent-carrying wire?

If the batteries are new, studentsmay see a very slight movementof the paper clip. Most likely themagnetic force from one strandof wire will not be great enoughto move the paper clip.

1c. Attach one end of the wire to one endof the battery. Move the coil very

near the bottom part of the “V” of the paper clip. Briefly touch the otherend of the wire to the battery to senda current through the coil. Is the

paper clip attracted to the current-carrying coil? How does the coil’sattraction compare to the attractionof a single strand of wire?

The coil should attract the paperclip, but not strongly. The attrac-tion from the coil, however,should be greater than the attrac-tion from just one strand of wire.

1d. Connect one end of the wire to oneof the battery terminals. Move thecoil near the end of the bottom of the

paper clip “V.” Briefly touch theother end of the wire to the other ter-

minal of the battery to send a cur-rent through the coil. Describe theextent to which the current-carryingcoil attracts the paper clip.

The coil wrapped on the drink-ing straw should slightly attractthe paper clip.

Next, place the nail into the end of the straw near the coil. Hold the headof the nail near the “V” and brieflysend a current through the coil. Howdoes the coil-and-nail’s attraction of the “V” compare to the coil’s attrac-tion alone?

Iron

Short here

F i g u re 2 . 7




The nail placed inside the straw

and coil should produce a signifi-cantly greater attraction than thecoil alone.

2. How can we increase the strength of an electromagnet?

As the number of coils or wind-ings increases, the strength of theelectromagnet increases. (Thenumber of paper clips picked up

by the electromagnets also de-

pends on whether the battery isin good condition or not.)

3a. Describe how the bulb in the circuitwith the electromagnet influencedthe strength of the electromagnet.

When a bulb is placed in the cir-cuit with an electromagnet, thestrength of the magnet decreases.

3b. How does the current (rate of elec-

trical flow) in an electromagnet de-termine the strength of the electro-magnet?

Lesser current produces a weakerelectromagnet. A greater currentproduces a stronger electromagnet.

3c. List the factors found in this activ-

ity that influence the strength of anelectromagnet.

The primary factors that influ-ence the strength of an electro-magnet are the number of coilsand the rate of electrical flow(current).

3d. Describe the relationship betweeneach factor listed above and thestrength of the electromagnet.

Increases in either will result in astronger electromagnet. Also, aniron core (such as a nail) inside acoil greatly increases the strengthof magnetism.




Topic: mag-lev trains


Code: CH006

Topic: MRIGo To: www.scilinks.org

Code: CH007

T E C H N O L O G I C A L T I E - I N

M a g - l e v Tr a i n s a n d M R I s

Electromagnets are used in some of the newest technology being de-veloped today. One project is the development of mag-lev (“magnetic levi-tation”) trains. These trains do not ride on wheels; in fact the train doesnot even touch the track. Strong electromagnets keep the train near thetrack but off the track. Strong electromagnets also propel the train downthe track. Without the friction of rolling wheels on hard track, the mag-lev trains will be able to travel faster (300 miles per hour) and with lessenergy and less pollution than the trains of today.

Magnets attract iron objects and attract or repel other magnets with-out touching them. Levitation occurs when an object is held up withouttouching another object. When magnets are involved in producing levita-tion, we call that “magnetic levitation.” Mag-lev trains hold up and pro-pel the train with electromagnets.

Ordinary electromagnets would not be strong enough to run mag-lev trains and would require a great deal of energy. Superconductors areused in making the very strong magnets needed to run mag-lev trains.Superconductors are materials that have no electrical resistance to the flowof electricity. Without electrical resistance, very strong magnets can beproduced. Certain materials become superconductors at very low tem-peratures. The materials have to be kept cold and this requires energy.

Scientists and engineers are working hard to create materials that becomesuperconductors at higher temperatures.

MRI (magnetic resonance image) machines are used in hospitals totake very detailed pictures of tissues inside the body. These machines makeimages by producing strong magnetic fields through which the bodymoves. The strong magnetic fields are produced by strong electromag-nets that are made with superconducting coils. These machines help doc-tors diagnose and treat disease. Again, electromagnets are used in newways that improve our lives.








A c t i v i t y 3


Making an

Electric Motor—Electromagnetism in Action

B a c k g ro u n d

The last activity focused on electromagnetism and factors that deter-mine the strength of magnetic interaction. Scientists and engineers haveused their knowledge of electromagnets to create simple electromagnetic

devices (doorbells, switches, circuit breakers, sound speakers, etc.) that arevery much a part of our everyday lives. One of the more complex, ingen-ious, and useful devices is the electric motor. Electric motors are all aroundus, turning VCR tapes, CDs, computer disk drives, can openers, tooth-

brushes, refrigerator and air conditioner pumps, drills, saws, fans, and more.Each electric motor turns because of electromagnets and electromagneticinteraction. In this activity, you will build an electric motor out of commonmaterials, including plastic drinking cups, wire, batteries, plastic drinkingstraws, and magnets. Although the motor you build will not be able to ac-complish much, it should provide you with a basic understanding of howreal electric motors work. You will learn that “timing is everything.” Fur-

thermore, as you persist in getting your motor to work, you may under-stand better the persistence and problem solving required to create a usefulproduct that works reliably.

Your teacher will either provide you with the rotor, flopper switch, andpenny switch for this activity or guide you through constructing them.

Topic: electric motor


Code: CH008






M a t e r i a l s

For each group:For Part 1—the

“strobe” light

■ one rotor on its stand

(see Figure 3.1)

■ one flopper (with

washer) (to make a

flopper, see page 42)

■ one penny switch

(with wires attached)

(to make a penny

switch, see page

39–42)

■ two 1.5-volt dry cells

in dry cell holders

■ one light bulb in a

socket

■ two 15-cm wires

■ masking tape


■ An electric motor can be built from available simple materials (magnets,wire, batteries, cups, etc.).

■ Electric motors work because of the interaction between electromagnetsor because of the interaction between electromagnets and permanentmagnets.

■ Rotors are what move in motors and the rotors are pushed around be-cause the magnets on them interact with other magnets in the motor.

■ For electric motors to work, electromagnets must turn on and off at justthe right times.

P a rt 1 — Bu i l d i n g a “ S t ro b e ” L i g h t

1 Set up the rotor as shown below (Figure 3.1). Leave at least a 30 x 30-cmarea of empty tabletop in front of the rotor. Position the cup stands so thatthe rotor easily rotates or spins, but does not move sideways by more thana centimeter. When you have properly placed the rotor and stands, tape thecup stands to the tabletop.

2 Adjust the position of the washer on the flopper so the flopper tips up

slightly on the magnet end (Figure 3.2).

End of small loop

of paper clip

Rotor

magnet0.5 cm 0.5 cm

F i g u re 3 . 1




Flopper straw Small loopof paper clip Large loop

of paper clip

Adjuster straw

Washer

Flopper magnet

Fulcrum

M a t e r i a l s

… c o n t ’ d .

For Part 2—

the electric motor

■ one electromagnet

on its cup stand

■ all the above

materials except one

15 cm wire and the

bulb and its socket

■ additional materials

as listed in the

Teacher’s Guide,pages 38–39

F i g u re 3 . 2

3Rotate the rotor and hold it so one of its magnets is as close to thetable as possible (directly under the middle of the rotor). Slide the mag-

net end of the flopper under the rotor so the magnet of the flopper isdirectly under the lowest rotor magnet. The rotor magnet and the floppermagnet should repel one another and the magnet end of the flopper shouldtip down. The objective is to get the magnet end of the flopper to tipdown when a rotor magnet is at the lowest point and to tip up after arotor magnet moves by the lowest point. It may be necessary to bend thepaper clip holding the flopper magnet in order to move the flopper mag-net closer to the rotor magnet. After making adjustments, tape both sidesof the fulcrum to the table. Make a final test by rotating the rotor. Themagnet end of the flopper should move down when a rotor magnet comesclose to it and then should move back up after a rotor magnet goes by(Figure 3.3).

Rotor magnet

Adjuster straw

Washer

Flopper magnetrepelled downward

Rotor

Fulcrum

F i g u re 3 . 3




Adjuster straw(twist to raise or lower

center penny)

Wire

Penny switch

Wire

Center penny stringtaped to adjuster straw

4 Move the penny switch

under the back portion of theflopper as shown in Figure3.4. One edge of the adjusterstraw should be midway be-tween the side pennies of thepenny switch. Make sure theshiny side of the middlepenny is facing up. Use avery small piece of tape totape the string of the middlepenny to the middle of theadjuster straw. Make surethere is at least 3–4 cm ofstring between the middlepenny and the straw. Twistthe adjuster straw to shortenor lengthen the penny string.When everything is in place,tape both sides of the pennyswitch to the table.

5 Challenge: Your set-upshould look something like

Figure 3.5. Create a circuitso that the light bulb blinkson and off as the rotor is

turned. Do not remove the wires from the penny switch. Try not to move the flopper. Use theadjuster straw to raise and lower the middle penny of the penny switch. Draw “wires” on Figure3.5 to show how you connected the various parts to create the “strobe” light.

6 When the rotor magnet is directly over the flopper magnet, what does the flopper magnet do?What does the switch end of the flopper do? Write your answers here.

F i g u re 3 . 4




F i g u re 3 . 5

7 When a rotor magnet is directly over the flopper magnet, what hap-pens to the middle penny of the penny switch? Write your answers here.

+-

-

+

Rotor

Washer

Flopper

Penny switch




8 When a rotor magnet is directly over the flopper magnet, is the pennyswitch on (conducting electricity through it) or is the penny switch off?

9 When there is no rotor magnet directly over the flopper magnet, de-scribe what happens to the flopper magnet and describe what happens tothe switch end of the flopper.

1 0 When no rotor magnet is directly over the flopper magnet, describewhat the flopper is doing to the middle penny of the penny switch.

1 1When no rotor magnet is directly over the flopper magnet, is the pennyswitch on (conducting electricity through it) or is the penny switch off?

P a rt 2 — B u i l d i n g a n E l e c t r i c M o t o r

1 2 Put away the bulb and its socket. Place the electromagnet so that itis as close as possible to the rotor magnets but does not touch any of therotor magnets as they pass by (Figure 3.6). Thoroughly tape the electromag-net cup to the table. Any movement of the cup and electromagnet will re-duce the operation of the motor.




Wire coil

Rotor Electromagnet0.5 to 1.0 cm

3.0 to 5.0 cm

60 cm

60 cm

F i g u re 3 . 6

S o m e n o t e s a n d h i n t s :

■ The electromagnet should repel the rotor magnets. If thisdoes not occur, change the direction of the currentthrough the electromagnet by turning the batteries

around or by switching the electromagnet wires in thecircuit.

■ Adjust the position of the washer on the flopper. Youmight try to get the motor to work without the washer.

■ Try spinning the rotor in different directions. One direc-tion may work better than the other direction.

■ Try spinning the rotor slowly or giving the rotor a gentle, but fast spin.

■ Twist the adjuster straw to raise and lower the middle

penny of the penny switch.■ All electrical contacts must be good. You may have to

use sandpaper to clean the contact points. Make sure theenamel has been removed from the ends of all wires.

■ Make sure your batteries are fresh. Do not leave a closedcircuit on for very long. A closed circuit through an elec-tromagnet will quickly wear out the batteries.

1 3 Challenge :

Arrange the batteriesand wires so that whenthe rotor is gently spun,the rotor keeps spinningdue to the interaction ofthe rotor magnets andthe electromagnet. Ar-range your set-up sothat the electromagnetrepels each of the rotormagnets. Draw “wires”

on Figure 3.7 to showhow you connected theobjects to get the motorto work.

1 4Consider what is happen-ing when a rotor magnet is di-rectly over the flopper magnet.When this occurs, another rotor

magnet is very close to (almostdirectly in front of) the electro-magnet. The penny switch should

be on and electricity should beflowing through the electromag-net. Recall that the current-carry-ing electromagnet and the rotormagnets have the same poles fac-ing each other. In this position,describe below what the electro-magnet is doing to the rotor mag-net near it.




F i g u re 3 . 7

+-

-+

Electromagnet

Rotor

Washer

Flopper

Penny switch




1 5 Now consider what is happening when there is no rotor magnet

directly over the flopper magnet. In this case, the electromagnet is in- between two rotor magnets. One rotor magnet is moving away from theelectromagnet and one is moving toward the electromagnet. Now the pennyswitch should be off and no electricity should be going through the electro-magnet. Explain below why it is a good idea to have the electromagnetturned off as a rotor magnet moves toward the electromagnet.

H o w R e a l E l e c t r i c M o t o r s Wo r k

Small electric motors, like the motor made in this activity, turn becauseof the magnetic interaction between electromagnets and permanent mag-nets. Usually there are a number of coils or electromagnets in the motor. Tomaximize turning, these electromagnets must turn on at precise moments.

In larger motors there are no permanent magnets. The motors operatedue to the magnetic interaction between electromagnets. Again, timing is

everything. The electromagnets must turn on or change their polarity atprecise moments to maximize the turning.

Small motors use a number of electromagnets rather than just one. Inaddition, real motors use a commutator and brushes, instead of floppersand penny switches, to turn the electromagnets on and off. The commuta-tor rotates with the coils. The brushes remain stationary and conduct elec-tricity from the power supply to the commutator. The commutator thenconducts the electricity to just one of the coils at a time. The commutator isinsulated so electricity is not conducted from coil to coil.

In Figure 3.8, notice that coil A is receiving electricity from the brushesthrough the commutator. Coil B is not in contact with the brushes and is

not receiving electricity. With current flowing through coil A, a magneticfield is created around coil A. This magnetic field interacts with the mag-netic field of the permanent magnets and rotates all the coils and the com-mutator. As the coils and commutator rotate, the brushes lose contact(through the commutator) with coil A and make contact with coil B. Coil Bthen turns on and coil A turns off. The drawing shows just one loop in eachcoil. Real coils have many loops wrapped around iron cores and can createvery strong magnetic fields.




To power

To power

BrushBrush

Insulator

Commutator

Coil A

Coil B

Permanentmagnet

Permanentmagnet

F i g u re 3 . 8





In this activity, students build anelectric motor from common objects.

In doing so, they see how the mag-netic interaction between a perma-nent magnet and electromagnet pro-duces the rotation of the rotor (seeFigure 3.19). They also see how aflopper and penny switch maintainrotation of the rotor by turning theelectromagnet on and off at the rightmoments.

The direction of the currentthrough the electromagnet is chosen

so the electromagnet repels the per-manent magnets on the rotor. Therepelling force turns the rotor. Theelectromagnet turns off as a perma-nent magnet rotates toward it. Thisallows the permanent magnet to ap-proach the electromagnet without

being repelled by the electromagnet.


A c t i v i t y 3

Making anElectric Motor—

Electromagnetism in Action

Then, just as a permanent magnetmoves in front of the electromagnet,

the electromagnet turns on and re-pels the permanent magnet to pushit around. The flopper and pennyswitch work to turn the electromag-net on and off at the appropriatetimes. Students will have to trouble-shoot and make various changes toget the motor to work. Trial and er-ror, persistence, and creative prob-lem solving will lead to success!Once students understand the motorin this activity, they are better pre-pared to understand the presentationof how real motors work. The expe-rience is not unlike what scientistsand engineers go through as they cre-ate or improve devices. It takes mucheffort, testing, and sound thinking toproduce a device that works reliably.





At least two class periods of 40–60 minutes will be required to com-plete this activity and discuss the re-sults.


The first time this activity isused, significant preparation is re-quired. However, since the batteriesare the only consumable items, youcan save your motors for use withfuture classes.

There should be one motor foreach group of three to four students(eight to ten motors per class ofstudents). Before constructing all ofthe materials for class use, youshould build a working model foryourself so you are familiar withthe construction and operation ofthe motor.

There are a number of different

approaches to constructing the partsof the motor. You can (a) construct allthe parts yourself; (b) enlist a fewcareful students to help you with theconstruction; or (c) guide groups ofstudents in the step-by-step construc-tion of most of the parts.

M a k i n g t h e R o t o r a n d

R o t o r S t a n d s

a To make stands for the rotor, open

and straighten the large loops oftwo large paper clips. Tape theseclips to the bottoms of two cups(Figure 3.9). Make sure there isabout 1 cm of the small loop thatextends beyond the bottom of thecup. The end of the small loopwill prevent the rotor from rub-

bing against the stand.

b Glue two cups together to makethe rotor that will rotate on the

M a t e r i a l s

For theconstruction of one

motor:

■ five 1-inch-long

ceramic, rectangular

magnets (available

from Radio Shack ®

Cat. # 64-1879); not

always in stock—

purchase well in

advance

■ five 16-oz plastic drinking cups

■ three new pennies

■ three plastic drinking

straws

■ one 5-m piece of #24

enamel-coated

magnet wire (with

sanded ends)

■ two 60-cm pieces of

#24 enamel-coated magnet wire (with

sanded ends)


wire with stripped

ends

■ one large, iron nail

(approximately 8–10

cm long)

■ four 1.5-volt dry cells

(“C” or “D” size)

■ two battery holders

■ three large paper

clips (giant or jumbo

clips measuring

about 1 cm x 4.8 cm)

Rotorsupport

cup

1.0 cm

F i g u re 3 . 9




■ masking tape

■ one 4 cm x 8.5 cm-

piece of cardboard

from one tablet-back

■ one 18 cm x 2.5 cm-

and two 3 cm x 4 cm-

pieces of corrugated

cardboard

■ one 4 cm x 6 cm-

piece of medium or

fine grit sandpaper

■ one tube of silicon

glue

■ one light bulb (#48 or

1.5–3 volt) in its

socket

■ vinegar and salt (to

clean the pennies)

■ one 3 cm x 0.2 cm-

iron washer


sewing thread

■ utility knife

■ scissors

■ stapler

■ pliers

■ heat source

paper clips of the stands. Melt a

small hole into the bottom of eachof these rotor cups. Open up oneloop of a large paper clip. Usepliers to hold the end of the pa-per clip in a flame. Use the hotend of the paper clip to melt asmall hole in the bottom of eachcup. The hole should be centered,small, and smooth so the rotorrotates freely and evenly.

c To indicate where to place the

permanent magnets on the rotor,draw a square with sides equalto the diameter of the cup. Drawdiagonal lines from corner to cor-ner in the square. Place the cupupside down inside the squareand mark the rim where the linescross the rim.

d Use silicon glue to glue the rimof the marked rotor cup to the rim

of the other rotor cup. Make sureyou can see the marks when thetwo cups are glued together.

e After the glue on the rotor cupsis dry, tape (or glue) the four rec-tangular magnets to the rims ofthe cups at the marked positions.Make sure that the same pole(north or south) faces outward onall four magnets. In other words,the outward facing side of each

magnet should repel the outwardfacing side of all the other mag-nets. Make sure that your lastpiece of tape is along the rims, notacross the rims. This reduces thechance of a snag when you movethe electromagnet close to the ro-tor magnets.

M a k i n g t h e E l e c t ro m a g n e t

About 60 cm from one end of the5-m length of #24 magnet wire, startwrapping most of the wire aroundthe 3-cm section of nail near the headof the nail. Do not wrap the last 60cm of wire. Twist the two 60-cmlengths of wire together to keep themfrom unraveling from the coil. Tapethe nail to the bottom of a cup. Sandthe enamel off the last 3 cm of eachwire. When the electromagnet is

used, you will have to tape the cupwith the electromagnet securely tothe tabletop so that the head of thenail is about 1 cm from a magnet onthe rotor.

M a k i n g t h e P e n n y S w i t c h

The penny switch consists ofthree pennies. Two of the pennies areseparated from each other and are

attached to wires in the circuit. In between these two side pennies is thethird, middle penny. When thismiddle penny is lifted and touchesthe two side pennies, the switch isclosed and a current can pass alongthe chain of pennies.

a The pennies must be clean andshiny. To clean and shine the pen-nies, put the pennies in a con-tainer and add enough vinegar to

cover them. Rub salt over thepennies in this vinegar bath. Theobjective is to remove nearly allof the tarnish from the pennies.Sand both sides of all the pennies.

b Use masking tape to attach themiddle of a 20-cm piece of thread

M a t e r i a l s

… c o n t ’ d .




to one side of the middle penny(Figure 3.10). Trim off any excesstape.

c Staple the two 3 cm x 4 cm-piecesof corrugated cardboard to the 4cm x 8.5-cm piece of tablet-backcardboard as shown below (Fig-ure 3.11). Make sure there is 2.5cm of space between the twosmall rectangles. Cut a short slitin the middle of one long side ofthe base.

10 cm 10 cm

Penny

Tape holdingthread to penny

F i g u re 3 . 1 0

Corrugatedcardboard

Side view

Top viewBase for penny switch

Slit

4 . 0 c m

2.5 cm

8.5 cm

3.0 cm

Tablet-back cardboard

F i g u re 3 . 1 1

d Sand the enamel from the ends oftwo 60-cm lengths of #24 magnetwire. Make sure there is no enamelleft on the last 3 cm of wire.

e Use masking tape to tape the wiresto the two side pennies and to thecardboard as shown in Figure3.12. The side pennies should be0.5 cm apart. Press the maskingtape tightly to the wires and pen-nies to ensure solid contact be-tween the wires and pennies.

f Insert the middlepenny beneath the

two side pennies.The middle pennyshould have itsshiny side facing upand its taped sidefacing down. Insertthe string into theslit and adjust thestring until themiddle penny is inabout the position

shown in Figure3.13. The string inthe slit keeps thepenny in place. Theother end of thestring will be tapedto the adjuster strawof the flopper (Fig-ure 3.13).




Side pennies

60-cmwire

60-cmwire

Side view

Topview

Side pennies and wires taped to penny switch base

60-cmwire

Slit

60-cmwire

0.5 cm

F i g u re 3 . 1 2

String to be taped to

adjuster straw of

flopperShiny side up;

taped side down

String in slit

F i g u re 3 . 1 3




M a k i n g t h e F l o p p e r

a Tape a 17-cm section of plasticdrinking straw (flopper straw) toan 18 cm x 2.5-cm piece of corru-gated cardboard as shown in Fig-ure 3.14. Start the straw 3 cm fromone end of the cardboard.

b Cut an 8-cm length of plastic

drinking straw (adjuster straw),crimp the one end, and insert thecrimped end about 1–2 cm intothe extended end of the flopperstraw. The adjuster straw shouldfit snugly inside the flopperstraw, but should be able to turninside the flopper straw.

17-cm plastic straw

Adjuster straw goes here

18 cm 3 cm

2 . 5 c

m

F i g u re 3 . 1 4

Side view

Small loop

Top view

Large loop

F i g u re 3 . 1 5

c Bend open the largeloop of a large paperclip as shown in Fig-

ure 3.15.

d Tape the small loopend of the paper clipto the end of theflopper as shown inFigure 3.16.

e Insert a rectangular magnet in thelarge loop of the paper clip. Makesure that the side facing upwardrepels the magnets on the rotor.

It is important to have theflopper magnet and each of therotor magnets repel one another.

f Place the washer under theflopper straw about midway be-tween the edges of the tape hold-ing the straw to the cardboard.Move the 12-cm section of plas-tic drinking straw (fulcrum) un-der the flopper until the flopper

just about balances. Tape the ful-crum to the underside of theflopper. Move the washer for-ward or backward along theflopper to make adjustments.




R e m i n d e r s a n d Tro u b l e

S h o o t i n g

When you introduce the activi-ties, draw students’ attention to thedrawings and materials, and go overthe names of objects (rotor, flopper,magnet end of the flopper, pennyswitch, etc.). This should help them

better understand the challenges andquestions.

It is unlikely that all students willconstruct a motor that works per-fectly. Therefore, you will have to beprepared to encourage persistence introubleshooting and problem solv-ing. Some potential problems (andsolutions) follow:

■ dry cells may be weak (add morecells in series)

■ the batteries may not be connectedin series (+ end of one connectedto the – end of the other)

■ the washer may be too far forwardor too far back

■ the adjuster straw may have to beturned one way or the other toraise or lower the middle penny ofthe penny switch

■ the electromagnet may not be re-

pelling the rotor magnets (changethe direction of current throughthe electromagnet)

■ the wires attached to the side pen-nies of the penny switch may not

be making good contact with thepennies (disassemble, sand, andreplace)

■ the rotor magnets may not all re-pel the flopper magnet (flip over

one or more magnets)

■ the electromagnet may be movingwhen it interacts with the rotormagnets (securely tape down theelectromagnet and the supportcup of the electromagnet)

Remind students not to leavetheir motors on for very long. Evenif the motor is not running, currentcould still be running through the

electromagnet, wearing out the drycells.

The same motor may run in dif-ferent ways. When the washer is onthe flopper, the motor will often runslowly. Each passing rotor magnetpushes the flopper down and turns

Adjuster strawFlopper straw

Floppermagnet

Small loop ofpaper clip

Large loop ofpaper clip

F i g u re 3 . 1 6




on the electromagnet. When a rotor

magnet moves past the flopper mag-net, the flopper magnet moves up-ward and opens the switch at theother end. When you remove thewasher from the flopper, the motoroften runs relatively fast. In this case,the flopper is just rapidly jiggling upand down and is not flopping. Theon-off switching, however, is some-how still synchronized with the ro-tor rotation, but how?

In this high-speed case, withoutthe washer, you would think that theelectromagnet would always be on.Even when there is no rotor magnetclose to the flopper magnet, theweight of the flopper magnet (notcounterbalanced by the washer)should keep the magnet end downand the switch on. Then, when a ro-tor magnet passes by, the floppermagnet should be pushed furtherdown, keeping the electromagnet on.

Since this is not likely the case, some-thing else must be occurring.

One possible explanation is thatthe flopper magnet might be re-

bounding upward after beingpushed down by a rotor magnet andheld in place by the middle pennystring. This upward rebound of theflopper magnet might be enough totip down the middle penny, break thecircuit in the penny switch, and turn

off the electromagnet.


You may want to challenge stu-dents to make changes that maketheir motors run faster (or slower).

You may also challenge them to cre-

ate a reliable switch that can replacethe flopper and penny switch. Someelectronics stores have reed switchesfor sale. The “reeds” in these switchesare conductors that come together inthe presence of a magnetic field andclose the circuit. A reed switch might

be an effective substitute for theflopper and penny switch.

Once the motor has operatedsuccessfully, students may want tosee what happens when there arechanges in the number of coils in theelectromagnet, the number of batter-ies in series, the distance between theelectromagnet and rotor magnets,and the position of the rotor magnets.

Some students may want toplace both the electromagnet and the

bulb in the circuit so the motor runsand the light blinks. However, theresistance of the bulb usually re-duces the current in the circuit to the

point where the strength of the elec-tromagnet is not great enough to runthe motor.

Students may want to find somereal motors that no longer work, care-fully open them, and observe thecommutator, coils, and brushes. Cau-tion students not to attach powersources to these dismantled motors.Serious injury may occur.

Students may also want to build

a very simple electric motor (Figure3.17):

a Tape a “D” battery to the bottomof a cup.

b Place the magnet, with poles onthe large faces, on the side of the

battery.




c Bend two large paper clips as

shown in Figure 3.17. Hold the pa-per clips to the battery with a rub- ber band or with masking tape.

d Wrap a meter of 24-gaugeenamel-coated magnet wirearound a toilet paper tube to cre-ate the coil. Make sure there isenough wire at the ends to wraparound the coil to hold the coiltogether and to extend out fromthe coil about 5 cm.

e Sand the enamel off the 5-cmends of the coil.

f Bend and move the end coil wiresso they are in line with the axisof the coil.

g Place the coil in the paper clipcradle and gently spin the coil.

h Bend the paper clips and move

the magnet to adjust the relativeposition of the coil and magnet.

i Press the paper clips to the ter-minals of the battery.

j With some trial and error adjust-ments, the coil should begin spin-ning. The coil spins as its mag-netic field interacts with themagnet field of the permanentmagnet. The momentum of the

coil carries the coil through thoseregions where the magnetic inter-action resists the motion of thecoil.

k Since a short circuit is created, thecoil and cradle wires could gethot. Remove the coil from the

Battery

Magnet

Coil

Sand enamel off

ends of coil

F i g u re 3 . 1 7

cradle if the coil and wires startheating up.

Answers to questions found within the

Student Worksheet on pages 30–35.

5. Draw “wires” on Figure 3.5 to showhow you connected the various partsto create the “strobe” light.

The correct connections for the“strobe” light are shown in Fig-ure 3.18.

6. When the rotor magnet is directlyover the flopper magnet, what doesthe flopper magnet do? What doesthe switch end of the flopper do?




+-

-+

Rotor

Washer

Flopper

Penny switch

F i g u re 3 . 1 8

When a rotor magnet is directlyover the flopper magnet, theflopper magnet moves down-ward and the switch end of the

flopper moves upward.

7. When a rotor magnet is directly overthe flopper magnet, what happens tothe middle penny of the pennyswitch?

When a rotor magnet is directlyover the flopper magnet, theswitch end of the flopper pullsthe middle penny upward.

8. When a rotor magnet is directly overthe flopper magnet, is the pennyswitch on (conducting electricitythrough it) or is the penny switch off?

When the switch end of theflopper pulls the middle pennyupward, the middle penny




touches the two side pennies,

closes the penny switch, and al-lows electricity to flow throughthe switch. The penny switchis on.

9. When there is no rotor magnet di-rectly over the flopper magnet, de-scribe the movement of the floppermagnet and describe the movementof the switch end of the flopper.

When no rotor magnet is directly

over the flopper magnet, theflopper magnet moves upwardwhile the switch end of theflopper moves downward.

10. When no rotor magnet is directlyover the flopper magnet, describewhat the flopper is doing to themiddle penny of the penny switch.

When no rotor magnet is directlyover the flopper magnet, the

switch end of the flopper movesdownward and allows themiddle penny to move down-ward away from the side pennies.

11. When no rotor magnet is directly overthe flopper magnet, is the pennyswitch on (conducting electricitythrough it) or is the penny switch off?

When the switch end of theflopper moves downward and

allows the middle penny to movedownward away from the sidepennies, the middle penny breakscontact with the side pennies andopens the penny switch so noelectricity flows through it. Thepenny switch is off.

13. Draw “wires” on Figure 3.7 to show

how you connected the objects to getthe motor to work.

The correct connections for themotor are shown in Figure 3.19.

14. When a rotor magnet is directly overthe flopper magnet, another rotormagnet is almost directly in front of the electromagnet. With the pennyswitch on and electricity flowingthrough the electromagnet, describe

what the electromagnet is doing tothe rotor magnet near it.

With the penny switch on, elec-tricity should be moving throughthe electromagnet and the elec-tromagnet should be magne-tized. Since the electromagnetand the rotor magnet are ar-ranged to repel one another, theelectromagnet should be repel-ling the rotor magnet that is di-

rectly in front of it. The repellingforce rotates the rotor.

15. In a case where the electromagnet isin-between two rotor magnets, onerotor magnet is moving away fromthe electromagnet and one is mov-ing toward the electromagnet. Ex-

plain why it is a good idea to havethe electromagnet turned off as a ro-tor magnet moves toward the elec-

tromagnet.

Knowing that the electromagnet(when on) and rotor magnets re-pel one another, it is a good ideato turn off the electromagnet sothat an approaching rotor mag-net is not repelled by the electro-magnet.




+-

-+

ElectromagnetTouch wiresto start motor

Rotor

Washer

Flopper

Penny switch

F i g u re 3 . 1 9




A c t i v i t y 4


Motion,

Magnetism, andthe Production of Electricity

Topic: generators


Code: CH009

B a c k g ro u n d

When Hans Christian Oersted discovered that a current-carrying con-ductor produces magnetism, the opposite process surely came into ques-tion: Can magnetism produce electricity? Oersted and others tried to pro-

duce electricity from magnetism, but it wasn’t until 1832—twelve years afterOersted’s discovery—that Michael Faraday, an English physicist, and Jo-seph Henry, an American physicist, independently and simultaneously pro-duced electricity from magnetism. Faraday gets the credit because he wasfirst to publish his discovery. What Oersted and others missed, but whatFaraday and Henry discovered, was that in order to produce electricity frommagnetism, it is necessary to move the magnet or the wire. In this activity,you will observe how motion and magnetism can produce electricity and inthe process you will be building a generator.


■ A generator can be built from available simple materials (magnets, wire,etc.).

■ If a closed circuit coil is moved in a magnetic field, an electrical current isproduced in the coil and circuit.

■ Motion and magnetism create the electricity that we use in our homes,schools, and businesses.






M a t e r i a l s

For each group:

■ one 3-m piece of 24-

gauge enamel-

coated wire (for the

rotating coil)


24-gauge enamel-

coated wire (sand the

enamel from 4-cm

sections at the end of

the wires)

■ two pieces of 20-

gauge copper wire,

each about 20 cm

long

■ two strong ceramic or

rubberized magnets

with the poles on the

larger surfaces or

faces. The magnets

can be circular or

rectangular and should measure

about 1.6 cm to 2.5

cm across and about

0.3 cm thick.

■ masking tape

■ wire cutters

■ one 7-cm x 11.5-cm

piece of medium or

fine grit sandpaper

(used to sand the

enamel from the

ends of the wires)

■ a felt-tipped marker to

wrap the coil around

(optional)

■ Stronger magnets, more loops in the coil, and a faster spinning coil pro-

duce more current.■ Some power plants use fossil fuel or nuclear energy to form steam that

turns coils to produce electricity. Other power plants use wind and mov-ing water (streams and rivers) to turn coils to produce electricity.

P ro c e d u re

1 As noted in the Background section above, electricity can be producedin wires from magnetism and either movement of the wire or movement ofthe magnet (WIRES + MAGNETISM + MOVEMENT = ELECTRICITY IN

THE WIRES). Movement of magnets might cause movement in the needlesof the current detectors. Therefore, to make sure that the movement in theneedles is caused by electricity and not by moving magnets, it will be betterto keep the magnets still and move the wires.

2 One way to make a lot of wire move rapidly in a small space is to createa coil of wire and have that coil spin in a cradle. If a coil has not been pro-vided, make a coil by following the directions at the end of this activity(“How to Make the Rotating Coil,” pages 58–60).

Cradle

Top view of cradle

3.5 - 4 cm

2.3 cm

Right angle bends

"Tails"of cradle

F i g u re 4 . 13 Making the Cradle

for the Rotating Coil(Figures 4.1 and 4.2). Thecradle consists of twocopper wires (each 20 cmlong) that hold the rotat-ing coil and allow it tospin. At least 5-cm sec-tions of the ends of thesewires must be bare cop-per wire (no plastic insu-lation or enamel). The

cradle conducts any elec-tricity generated by therotating coil to the cur-rent detector (galvanom-eter or coil and compass).The two pieces of 20-gauge wire (heavy wire)are bent into the shapes




M a t e r i a l s

… c o n t ’ d .

■ a current detector

(either a

galvanometer or a

coil and magnetic

compass)

If a galvanometer is

not available, the

following materials

are needed to

make a current

detector from acoil and magnetic

compass (See

“How to Make a

Current Detector”

on page 60):

■ one directional,

magnetic compass

(the compass must

not “lock up” or

“stick” when the

needle is stationary)

■ one 4.5-m piece of

24-gauge, enamel-

coated wire (for the

compass coil). Sand

the enamel from 4-

cm sections at the

ends of the wire.

■ one square piece of

cardboard (tablet-

back thickness) with

sides that are about 1 cm longer than the

diameter of the

compass body

~2.3 cm

Rotating coil

Side view of cradle

F i g u re 4 . 2

as shown in Figures 4.1 and 4.2 and are taped to the table about 3.5 cm to 4cm apart. The bottom of the cradle loops should be about 2.3 cm off thetabletop. Note in the top view that there are right-angle bends in the wireon the table. The cradle is more secure when the right-angle bends are se-curely taped to the table.

4 Connecting the Current Detector to the “Tails” of the Cradle. Use thetwo 40-cm pieces of 24-gauge wire to connect the “tail” of the cradle to thecurrent detector (see Figure 4.3). Make sure that 4-cm sections of the ends ofthe wires have been sanded to remove the enamel. Also, it might help tosand the “tails” of the cradle as well. Move the current detector at least 20

cm away from the rotating coil and cradle.If a compass and coil are used as a current detector, rotate the compassand coil on the tabletop until the compass needle lines up with the top ofthe coil. Since any movement of the compass and coil will make it hard todetect needle movement, tape the compass support to the table. Also, tapedown wires leading to the compass and coil.

5 Giving the Coil a Spin. Once the cradle has been connected to the cur-rent detector, place the rotating coil in the cradle. Using one of the “tails” ofthe rotating coil, give the coil a spin. Movement of the needle of the currentdetector indicates that electricity was produced in the rotating coil. Was

there any evidence that the electricity was produced in the rotating coil?




M a t e r i a l s

… c o n t ’ d .

Optional Materials

for Making a Magnet

Holder (See “How to

Make a Magnet

Holder” on page 61) :

■ one rectangular piece

of cardboard (tablet-

back thickness),

approximately 1 cm x

8 cm

■ one giant or jumbo paper clip

(approximately

4.8 cm x 1 cm)

■ one 4-cm section of

plastic drinking straw

■ one “D” battery or

beaker. Since the

battery is used only

to hold a magnet, the

battery can be dead.

6 Challenge: Figure out how to use one or both magnets with the rotat-ing coil to produce and detect electricity. Recall that sandwich magnets havepoles on the large, flat surfaces (not on the ends). Also, recall that like polesrepel and different poles attract. The position of the poles will likely be

important in meeting this challenge. One person may want to hold the mag-nets while another person spins the rotating coil. A third person may wantto watch the current detector. Whenever a test is made, make sure that themagnets are not moving.

Cradle

Rotating coil

Current detector(Galvanometer or

compass and coil)

40 cm

40 cm

"Tails"of cradle

F i g u re 4 . 3




Describe how you hold the magnets around the rotating coil to produce

and detect electricity. The poles are important. Try to discover and describehow the poles should be placed.

7 Once electricity is produced and detected, answer the following ques-tions through experimentation:

a Try spinning the coil in different directions. How is the direction of coilspin related to the direction in which the needle moves?

b Compare needle deflection for slow spinning and fast spinning. Howdoes the rate of spin relate to the extent of needle deflection and conse-quently to the electrical current in the wire?




c What do you think would happen to the deflection and current if just

1 m of wire, rather than 3 m, was used to make the rotating coil?

d What do you think would happen to the deflection and the current ifweaker magnets were used?

8 Faraday’s Law. Michael Faraday and Joseph Henry independently dis-covered that a current could be produced in a closed circuit coil if that coilmoved relative to a magnetic field or region of magnetic influence. The coilmust move and/or the magnetic field must move such that the coil wiresmove across the magnetic field, which runs from north pole to south pole.The production of electricity from motion and magnetism is called electro-magnetic induction.

Faraday was first to get his discovery published so he gets most of thecredit for discovering electromagnetic induction. Faraday also had a lawnamed after him, “Faraday’s Law of Induction.” In terms of this activity,

Faraday’s law would predict that if the number of loops in the coil is doubledand if the coil spins twice as fast (cuts the magnetic field twice as often), theinduced current would be four times as great (assuming the same resis-tance).

9 The Production of Electricity for the Community. The electricity thatis made available to your home and community is produced in a way that isvery similar to the way electricity was produced in this activity. In your




community or in a community

nearby there is an electrical powerplant. In that plant, coils of wire aremoved in a magnetic field. As a con-sequence, an electrical current is pro-duced in the coils and in the wiresleading to your home where the elec-tricity is used to run your electricaldevices.

In this activity, chemical energyin you was transformed into energyof motion (spinning the coil), whichwas transformed into electrical andmagnetic energy (current in thewires), which was transformed backinto energy of motion (movement ofcurrent detector needle). In electricalpower plants, motion energy (spin-ning of coils) is transformed into elec-trical and magnetic energy.

Power plants have different waysof moving the coils. For some (hydro-electric plants) running or falling wa-ter from rivers is used to turn the coils.

For others, coal or gas (fossil fuel) is burned to produce steam, which turnsthe coils. For still others, nuclear en-ergy is used to produce steam, whichturns the coils. In some cases (wind-mills), wind is used to turn the coils.It can be said that we get most of our

electrical energy from moving air or

water (liquid or gas).How fascinating it is to think thatenergy from some cold stream milesaway is transmitted almost instantlyto the warm computer on which thissentence is being typed and stored…and to think that others are dippinginto that same stream for the energyused to run their computers, lights,and innumerable gadgets.

Less than two and a half life-times ago we did not know how toproduce electricity from magnetism.Thanks to Faraday and Henry, notonly do we now know how to dothat, but we have built on that foun-dation to create a wondrous collec-tion of electrical systems and devices.Communication around the worldused to take months or years. Now,even without connecting wires, wecan communicate with minimumdelay in words and pictures with

nearly anyone in the world. The dis-covery of electromagnetism and elec-tromagnetic induction has shrunk thehuman world and stands as one ofthe most significant advances of the20th century.




Topic: conductors

Go To: www.scilinks.org Code: CH010

T E C H N O L O G I C A L T I E - I N

S u p e rc o n d u c t o r s

Scientists and engineers are working on improving the way we gen-erate and distribute electricity. Wires in the coils of generators and wires

between the power plant and our homes, schools, and businesses all re-sist the flow of electricity. If we could reduce that resistance so the elec-tricity could move more easily, then we would be able to use less energyto produce electricity and we would be able to reduce pollution that comesfrom the production of electricity. Scientists and engineers are workingon ways of reducing electrical resistance. They have already discoveredthat some materials at very low temperatures provide no resistance to the

flow of electricity. These materials are called superconductors. If we hadhighways that acted like superconductors, we could get our car up to 60miles per hour, shut off the engine, and coast at 60 miles per hour for aslong as we wanted to. We would not have to use fuel to move down thehighway; therefore we would save money and energy and have a cleanerenvironment. The problem at this point in time is that superconductorshave to be kept super cold. Keeping things cold (about 200 Celsius de-grees below the freezing point of water) requires the use of energy. Scien-tists and engineers are currently trying to create superconducting materi-als that operate at relatively high temperatures. Creating a superconductorthat operated at room temperature would revolutionize the electrical

world. Scientists and engineers are experimenting with superconductingpower lines and with superconducting electrical generators. If the super-conducting generators and power lines prove successful, we will prob-ably be able to cut our costs, energy requirements, and pollution to morethan half of what they are today.







A c t i v i t y 4

Motion,Magnetism, and

the Production of Electricity


In this activity, students learnhow to produce or generate electric-ity from moving a closed circuit (coil)

through a magnetic field. They con-struct a coil that spins in a cradle.Magnets held close to the spinningcoil create a magnetic field (region ofmagnetic influence) in which the coilspins. The wires of the coil cut acrossthe magnetic field between the twomagnets and a current is created inthe spinning coil, in the cradle, andin the current detector.

Students observe that the direc-

tion in which the coil is spun deter-mines the direction in which theneedle of the current detector is de-flected and hence the direction thecurrent is moving. They also learnthat when the coil is spun faster, thereis greater needle deflection, whichindicates greater current. In addition,

students learn that stronger magnetsand more loops in the spinning coilwould produce greater current (de-

flection).The simple generator made inthis activity is related to the genera-tors used by electrical power plants.Basically students learn that powerplants move coils in magnetic fieldsand in the process produce the elec-tricity used in homes and the com-munity. Energy is required to movethe coils, whether the coils are onclassroom desktops or in power

plants. Students learn that fossil fu-els and nuclear energy are used toform steam, which turns the powerplant coils. Students also learn thatwind and moving water (from riversand dams) are used to turn the coilsin the production of household elec-tricity.





Two class periods of 40–60 min-utes each should be enough time tocomplete the activity and discuss theresults. If galvanometers are avail-able, then less time is required sincestudents need not make the currentdetector from a compass and coil.Also, more time can be saved by hav-ing a couple of careful students helpafter school to make all the rotatingcoils for the class. Once these coils are

made they can be used repeatedly byother classes.


To save classroom time, use stu-dent help to cut all of the materialsprior to class (e.g., wires, sections ofdrinking straws, and the cardboardfor the compass and the magnetholders).

If a compass is being used to de-

tect currents, that compass should bein good working order. Very smallcurrents and their associated mag-netic fields will not deflect a compassneedle if that needle tends to stickwhen it is stationary. Check to seethat smoothly operating compassesare used in this activity. If a needledoes seem to stick, have the studentlightly tap the compass to set theneedle jiggling. With the needle jig-

gling, spin the rotating coil and lookfor evidence of deflection and cur-rent.

Also, if compasses are beingused to detect currents, warn stu-dents to keep magnets and iron ob-

jects away from their compasses. A

compass needle will be held in place

by a nearby iron object or magnet andtherefore might not be easily de-flected by the weak magnetic fieldfrom the coil around the compass.

H o w t o M a k e t h e R o t a t i n g

C o i l

1 About 15 cm from one end of the3-m wire, start wrapping the wirearound an index finger or a felt-tipped marker. Keep the wirerather snug around the object, butloose enough to get the coil off theobject. Leave about 15 cm of un-wrapped wire at the end of thewire. Wrap the two 15-cm endsabout three times around the coilon opposite sides of the coil. Cutthe wires so about 5 cm of wireextend outward on each side ofthe coil. These wires are the “tails”of the rotating coil (see Figure 4.4).

2 Sand only the tops of the 5-cm“tails” (wires) of the rotating coil.To do this, place a piece of card-

board at the edge of the table (seeFigure 4.5). Hold the coil in a ver-tical position on the edge of atable with one “tail” resting onthe cardboard. Sand the top of the“tail.” Also, sand the top of theother “tail.” Make sure the same

sides of the wires are sanded.Also, make sure the tops of thewires are sanded near the coil. Donot sand the wire that is in thecoil.

3 Straighten and bend the “tails” sothey line up through the middle




Rotating coil made from wrapping3 mm of wire around a felt-tipped marker or index finger

5 cm 5 cm

F i g u re 4 . 4

Side view

Cardboard toprotect table

Table

Sand topof wires

Leave enamel onbottoms of wires

F i g u re 4 . 5

F i g u re 4 . 6

F i g u re 4 . 7




Side view

Compass

Sand ends

Coil

Cardboard

Twist

F i g u re 4 . 9

Top view

CompassWrap wire here

F i g u re 4 . 8 of the coil. Make sure the wires

line up from two different views(see Figures 4.6 and 4.7). You willwant to bend the wires so the coilis well balanced and does notwobble when it spins in thecradle.

H o w t o M a k e a C u r re n t

D e t e c t o r

1 Cut a square piece of cardboardwith sides about 1 cm longer than

the outside diameter of the com-pass. Cut 0.5-cm notches in themiddle of two opposite sides ofthe square. The notches will holdthe coil of wire over the middleof the compass.

2 Place the center of the compassover the center of the square.Starting about 12 cm from oneend of the 4.5-m piece of wire,

wrap the wire around the com-pass and square and through thenotches. Stop wrapping whenthere is about 12 cm of wire left.Twist the two wires togetherclose to the compass. Sand theenamel off 4-cm sections at theends of the wires. (See top viewin Figure 4.8 and side view in Fig-ure 4.9.)

If the electrical current flowing

through the coil is great enough,the current will produce mag-netism strong enough to movethe compass needle.




H o w t o M a k e a

M a g n e t H o l d e r

A magnet holder can be used tohold a magnet over the rotating coil(Figure 4.10).

1 Tape a magnet to the end of the 1cm x 8 cm-piece of cardboard.

2 Tape a 4-cm section of plasticdrinking straw to a battery (deador alive) or beaker.

3 Bend the large loop of a jumbopaper clip so that the large loopis a right angle to the rest of thepaper clip.

4 Tape the large loop of the paperclip to the piece of cardboard as

shown.

5 Slip the small loop of the paperclip into the straw.

6 Slide the cardboard, clip, andmagnet up and down in the strawto adjust the height of the magnet.

1 cm x 8 cm cardboard

Magnet

Large loop of paper clip

Small loop of paper clip

inside straw

Slide up and down

to adjust magnet

Battery

4-cm section of straw

F i g u re 4 . 1 0

7 Set the magnet over the top of therotating coil.

Question: If this magnet is directlyover the rotating coil, where shouldthe other magnet be placed to pro-duce the greatest current in the coil?


Students may be challenged tosee how changes in the rotating coilmight produce more or less current(deflections). Will a rotating coilmade from 1 m of wire produce thesame deflection (current) as a rotat-

ing coil made from 3 m of wire? Doesthe gauge of the wire make a differ-ence? What will happen if weaker orstronger magnets are used?

Students may wonder why onlyhalf the enamel is removed from bothends of the rotating coil wire. If theenamel is removed from all around




the wire, the coil should produce an

alternating current. An alternatingcurrent is a current that changes di-rections back and forth in the conduc-tor. For half a turn of the coil the elec-tricity would travel in one directionand for the other half of a turn theelectricity would travel in the oppo-site direction. Alternating current inthe compass coil would produce analternating magnetic field and theneedle would jiggle back and forthafter an initial jump in one direction.

To produce an intermittent, di-rect current, and hence sustainedneedle deflection in one direction, theenamel is left on half the wire so thatno electricity flows to the compass

coil during that half of the turn.

How can we tell which way thecurrent should be traveling in a con-ductor that is moving across a mag-netic field? A left-hand rule for gen-erators or electromagnetic inductioncan be used. To implement the rule,point the thumb and index finger ofthe left hand perpendicular to oneanother. Point the thumb in the di-rection the conductor is moving andpoint the index finger in the directionof the magnetic field (from north poleto south pole). The middle finger,held perpendicular to both thethumb and index finger, will point inthe direction of the electron flow (seeFigure 4.11).

Direction

conductor

is moving

Direction of

magnetic field

(north to south pole)

Direction of

electron flow

F i g u re 4 . 1 1




Interested students may be chal-

lenged to use this left-hand rule todetermine the direction of electronflow in a coil that is rotating in amagnetic field. It may help to sim-plify the rotating coil by consideringonly one or two loops. Studentsshould discover that the currentmoves in one direction during onehalf of a spin and moves in the op-posite direction during the other halfof the spin.



5. Was there any evidence that the elec-tricity was produced in the rotatingcoil?

Here the students spin the coil inthe cradle, but without using themagnets. If magnets are not heldclose to the spinning coil, no elec-

tricity will be produced in the coiland no current will be detected.

6. Describe how you hold the magnets

Side view of cradle

Cradle

Note: Magnet

poles onopposite sides

of coils aredifferent

Rotating coil

Magnet

To current

detectorMagnet

N N N N N

S S S S S

N N N N N

S S S S S

F i g u re 4 . 1 2

■ Place one magnet directly un-

der the rotating coil. Wherewould you place the othermagnet to produce electricityin the spinning coil?

■ Hold the other side (pole) ofthe magnet close to the spin-ning coil.

■ The magnets need to be on op-posite sides of the spinningcoil.

■ The pole (or side of the mag-net) facing the coil might makea difference.

The magnet arrangement thatwill produce the strongest cur-rent will be one in which magnetsare held on opposite sides of thecoil, with different poles facingeach other (see Figure 4.12). Forexample, if one magnet is placed

close to and directly under thecoil and the other magnet is heldclose to and directly over the top

around the rotating coilto produce and detectelectricity.

Students meet thischallenge by holdingthe two magnets mo-tionless in various

places about the spin-ning coil. The chal-lenge can be difficult.Here are a couple ofhints to give studentsif frustration levelsrun too high.




of the coil and if the magnets’

poles closest to the coil are dif-ferent (magnets attracting), thenelectricity should be generated inthe spinning coil.

7a. How is the direction of coil spin re-lated to the direction in which theneedle moves?

When the direction of coil spin isreversed, the needle deflectionand current are reversed as well.

7b. How does the rate of spin relate tothe extent of needle deflection andconsequently to the electrical currentin the wire?

Faster spin produces greaterneedle deflection and greater cur-rent.

7c. What would happen to the deflection

and current if just 1 m of wire (ratherthan 3 m) were used?

A coil made with 1 m of wirewould produce less needle de-flection and current than a simi-lar coil made from 3 m of wire.

7d. What do you think would happen tothe deflection and current if weakermagnets were used?

Weaker magnets would produceless needle deflection and currentthan stronger magnets.




C i rc u i t

A circuit is a path of objects alongwhich an electrical current can flow.The circuit usually includes an elec-trical power source (battery or gen-erator) and wires that run to and fromthe power source.

C l o s e d C i rc u i t

A closed circuit is a circuit that hasan unbroken path of conductors thatrun to and from the power source.There are no non-conducting sectionsalong a closed circuit path.

C o i l

A coil is made when an insulatedwire is wrapped a number of timesaround an object in the same direc-

tion. Usually the wraps of wire lie ontop of or next to the other wraps ofwire. If the object is removed, thewire wraps are still considered to bea coil. When an electrical currentpasses through the coil, magnetismis created around each wrap. Sincemany wraps are on top of each otheror beside each other, the magnetismfrom each wrap adds up to producea strong magnetic effect (attraction)

around the coil.

C o n d u c t o r

A conductor is a material that elec-tricity or an electrical current can eas-ily pass though. Metals are usuallygood conductors of electricity.

C u r re n t

Current is a measure of how “fast”the electricity is moving in a conduc-tor. The speed is not measured inspeedometer speed (e.g., 50 miles perhour). It is measured by counting thenumber of charges (electrons or pro-tons) that pass any point in the con-ductor in one second. If you sat be-side a highway and counted thenumber of cars that passed you in asecond or minute or hour, you would

be measuring the “current” of cars(e.g., 35 cars in one hour). The “cur-rent” of cars would not be the sameas their speed (e.g., 50 miles perhour).

E l e c t r i c a l R e s i s t a n c e

Some materials allow electricity to

easily flow through them. Other ma-terials make it difficult for electricityto flow through them. Electrical re-sistance is a measure of how hard anobject resists the flow of electricitythrough it. Objects with high resis-tance put up a great resistance to theflow. Objects with low resistance putup little resistance to the flow. Forexample, the longer and skinnier awire is, the more resistance it has to

the flow of electricity.

E l e c t ro m a g n e t i c I n d u c t i o n

When a conductor is in a changingmagnetic field (region of magnetism),a voltage is produced (induced) in theconductor and that voltage can pro-

Glossary




duce an electrical current in the con-

ductor. This process is called electro-magnetic induction. The electricitythat we use in our homes, schools, and

businesses is produced by electromag-netic induction. Generators produceelectricity by electromagnetic induc-tion. In Activity 4, when the genera-tor coil spins between two magnets,the coil moves though different re-gions of magnetism. This produces anelectrical current in the spinning coiland this current is detected by thegalvanometer or the stationary coiland compass.

E l e c t ro m a g n e t i s m

Electromagnetism is the productionof magnetism in the space around awire carrying an electrical current.Also, electromagnetism is the pro-duction of magnetism in the spacearound a moving charged particle.

E l e c t ro n s

Electrons are negatively charged par-ticles that move around the nucleusof atoms. Electrons in metals are notheld tightly to the nucleus and canmove in metals. Electrons move inwires that are part of closed circuits.

G e n e r a t o r

A generator is a device that trans-forms energy of motion into electri-cal energy. In a generator, a coil andmagnetic field move relative to eachother. This movement produces orgenerates electricity in the coil. The

generated electricity is sent over

power lines to homes, schools, and businesses.

I n t e r a c t i o n

Interaction occurs when objects dosomething to each other. When a batstrikes a ball, the ball and bat hit eachother and therefore interact. When amagnet is moved near an iron object,the magnet and iron object attracteach other and therefore interact.

Magnets, whether permanent mag-nets or electromagnets, can interact(attract and repel) with each other.

M a g - l e v Tr a i n s

Mag-lev trains are trains that do nottouch the track as they move along.The train is both held off the track(levitated) and propelled down thetrack by strong electromagnets. With-

out the friction of wheels rollingalone a track, the mag-lev trains canmove very fast (over 300 miles perhour), very smoothly, and with littlepollution. Scientists and engineersare experimenting with these mag-netic levitation (mag-lev) trains.

M a g n e t i c F i e l d

The magnetic field is the region orspace around an object where thereis a magnetic effect. A magnetic ef-fect is the attraction of iron or the at-traction and repulsion of a magnet.A magnet, a current-carrying wire,and a moving charged particle pro-duce magnetic fields around them.



M a g n e t i s m

Magnetism is the property of attract-ing iron or steel objects.

N o n - c o n d u c t o r

A non-conductor is a material thatelectricity or an electrical currentdoes not easily pass through. Non-metals are usually good non-conduc-tors. Another name for “non-conduc-tor“ is “insulator.” An insulator

keeps electricity from passing fromone object to another object.

O p e n C i rc u i t

An open circuit is a circuit that has anon-conductor (air or other non-con-ductors) in the path that runs to andfrom the power source.

R o t o r

The rotor is a part of a machine thatrotates or spins around and doeswork. The interaction of magnetsmakes the rotor spin around in anelectric motor.

S h o rt C i rc u i t

A short circuit is a closed circuit thatpresents little resistance to the flow

f l t i it A h t i it i th

S u p e rc o n d u c t o r s

Superconductors are electrical con-ductors that offer little or no resis-tance to the flow of electricity. At thepresent time, superconductors existonly at very low temperatures.

V o l t a g e

To get charges to move in conduc-tors, the charges have to be pushed.Voltage is a measure of how hard the

charges are pushed. When the volt-age is high, the charges are given a

big push and carry lots of energy.When the voltage is low, the chargesare given a small push and carry alittle energy. In a circuit, when thevoltage is increased, the current in-creases if everything else stays thesame.

Charging Ahead - An Itroduction to Electromagnetism Malestrom

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Transcript of Charging Ahead - An Itroduction to Electromagnetism Malestrom