Magnetism and Its Uses · Chapter Resources Magnetism and Its Uses ... Teaching Transparency Activity ... Move the magnet at different speeds inside the coil and record the current

Glencoe Science

Chapter Resources

Magnetism and Its Uses

Includes:

Reproducible Student Pages

ASSESSMENT

✔ Chapter Tests

✔ Chapter Review

HANDS-ON ACTIVITIES

✔ Lab Worksheets for each Student Edition Activity

✔ Laboratory Activities

✔ Foldables–Reading and Study Skills activity sheet

MEETING INDIVIDUAL NEEDS

✔ Directed Reading for Content Mastery

✔ Directed Reading for Content Mastery in Spanish

✔ Reinforcement

✔ Enrichment

✔ Note-taking Worksheets

TRANSPARENCY ACTIVITIES

✔ Section Focus Transparency Activities

✔ Teaching Transparency Activity

✔ Assessment Transparency Activity

Teacher Support and Planning

✔ Content Outline for Teaching

✔ Spanish Resources

✔ Teacher Guide and Answers

Copyright © by The McGraw-Hill Companies, Inc. All rights reserved.Permission is granted to reproduce the material contained herein on the conditionthat such material be reproduced only for classroom use; be provided to students,teachers, and families without charge; and be used solely in conjunction with theMagnetism and Its Uses program. Any other reproduction, for use or sale, is pro-hibited without prior written permission of the publisher.

Send all inquiries to:Glencoe/McGraw-Hill8787 Orion Place Columbus, OH 43240-4027

ISBN 0-07-866119-6

Printed in the United States of America.

1 2 3 4 5 6 7 8 9 10 067 08 07 06 05 04

Glencoe Science

Photo CreditsSection Focus Transparency 1: Gabe Palmer/The Stock Market;Section Focus Transparency 2: Doug Martin;Section Focus Transparency 3: Bettmann/CORBIS

iii

To the Teacher iv

Reproducible Student Pages■ Hands-On Activities

MiniLab Observing Magnetic Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3MiniLab: Try At Home Making Your Own Compass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Lab Magnets, Coils, and Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Lab: Design Your Own Controlling Electromagnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Laboratory Activity 1 Comparing Magnetic Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Laboratory Activity 2 Creating Electromagnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Foldables: Reading and Study Skills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

■ Meeting Individual NeedsExtension and Intervention

Directed Reading for Content Mastery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Directed Reading for Content Mastery in Spanish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Enrichment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Note-taking Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

■ AssessmentChapter Review. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Chapter Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

■ Transparency ActivitiesSection Focus Transparency Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Teaching Transparency Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Assessment Transparency Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Teacher Support and PlanningContent Outline for Teaching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T2Spanish Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T6Teacher Guide and Answers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T12

Table of Contents

Additional Assessment Resources available with Glencoe Science:

• ExamView® Pro TestMaker• Assessment Transparencies• Performance Assessment in the Science Classroom• The Princeton Review Standardized Test Practice Booklet• MindJogger Videoquizzes• Vocabulary PuzzleMaker at: gpscience.com• Interactive Chalkboard• The Glencoe Science Web site at: gpscience.com• An interactive version of this textbook along with assessment resources are available

online at: mhln.com

Magnetism and Its Uses 1

Reproducible Student Pages■ Hands-On Activities

MiniLab Observing Magnetic Interference . . . . . . . . . . . . . . . . . . . . . . . 3MiniLab: Try at Home Making Your Own Compass . . . . . . . . . . . . . . . 4Lab Magnets, Coils, and Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Lab: Design Your Own Controlling Electromagnets . . . . . . . . . . . . . . . . . . . . 7Laboratory Activity 1 Comparing Magnetic Fields . . . . . . . . . . . . . . . . 9Laboratory Activity 2 Creating Electromagnets . . . . . . . . . . . . . . . . . . 13Foldables: Reading and Study Skills . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

■ Meeting Individual NeedsExtension and Intervention

Directed Reading for Content Mastery . . . . . . . . . . . . . . . . . . . . . . . . 19Directed Reading for Content Mastery in Spanish . . . . . . . . . . . . . . . 23Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Enrichment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Note-taking Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

■ AssessmentChapter Review. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Chapter Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

■ Transparency ActivitiesSection Focus Transparency Activities . . . . . . . . . . . . . . . . . . . . . . . . . 44Teaching Transparency Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Assessment Transparency Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

ReproducibleStudent Pages

2 Magnetism and Its Uses

Hands-OnActivities

Hands-On Activities

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Observing Magnetic Interference

Data and Observations

Analysis1. Which materials caused the paper clip to fall? Why do you think these materials interfered

with the magnetic field?

2. Which materials did not cause the paper clip to fall? Why do you think these materials did notinterfere with the magnetic field?

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Procedure 1. Clamp a bar magnet to a ring stand. Tie a thread around one end of a

paper clip and stick the paper clip to one pole of the magnet.

2. Anchor the other end of the thread under a book on the table. Slowly pullthe thread until the paper clip is suspended below the magnet but nottouching the magnet.

3. Without touching the paper clip, slip a piece of paper between the magnetand the paper clip. Does the paper clip fall? Note your result in the table.

4. Try other materials such as aluminum foil, fabric, or a butter knife. Writeyour findings in the table.

Material tested Result

Paper

Aluminum foil

Fabric

Butter knife

Other ___________


Name Date Class

Making Your Own CompassProcedure WARNING: Use care when handling sharp objects.

1. Cut off the bottom of a plastic foam cup to make a polystyrene disk.

2. Magnetize a sewing needle by continuously stroking the needle in the samedirection with a magnet for 1 min.

3. Tape the needle to the center of the foam disk.

4. Fill a plate with water and float the disk, needle-side up, in the water.

5. Bring the magnet close to the foam disk.

Hands-On Activities

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Analysis1. How did the needle and disk move when you placed them in the water? Explain.

2. How did the needle and disk move when the magnet was brought near it? Explain.

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Lab PreviewDirections: Answer these questions before you begin the Lab.

1. Why is the insulation removed from the wire?

2. What is the purpose of the galvanometer or ammeter in this lab?

Huge generators in power plants produce electricity by moving magnets pastcoils of wire. How does that produce an electric current?

Real-World QuestionHow can a magnet and a wire coil be used toproduce an electric current?

Materialscardboard tubescissorsbar magnetinsulated wiregalvanometer or ammeter

Goals■ Observe how a magnet and a wire coil

can produce an electric current in a wire.■ Compare the currents created by

moving the magnet and the wire coil in different ways.

Safety Precautions

WARNING: Be careful with scissors. Do nottouch bare wires when current is runningthrough them.

Procedure1. Wrap the wire around the cardboard tube

to make a coil of about 20 turns. Removethe tube from the coil.

2. Use the scissors to cut and remove 2 cm ofinsulation from each end of the wire.

3. Connect the ends of the wire to a gal-vanometer or ammeter. Record the readingon your meter.

4. Insert one end of the magnet into the coiland then pull it out. Record the current.Move the magnet at different speeds insidethe coil and record the current.

5. Watch the meter and move the bar magnetin different ways around the outside of thecoil. Record your observations in the Dataand Observations section.

6. Repeat steps 3 through 4, keeping the magnetstationary and moving the wire coil.

Magnets, Coils, and Currents

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Step 3:

Step 5:

Step 6:

Conclude and Apply1. How was the largest current generated?

2. Does the current generated always flow in the same direction? How do you know?

3. Predict what would happen if you used a coil made with fewer turns of wire.

4. Infer whether a current would have been generated if the cardboard tube were left in the coil.Why or why not? Try it.

Hands-On ActivitiesCommunicating Your Data

Compare the currents generated by different members of the class. What was the value ofthe largest current that was generated? How was this current generated?

(continued)

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Lab PreviewDirections: Answer these questions before you begin the Lab.1. Why is the safety symbol for extreme temperatures included in this lab?

2. What is the maximum voltage to be used in this lab?

You use electromagnets every day when you use stereo speakers, power doorlocks, and many other devices. To make these devices work properly, thestrength of the magnetic field surrounding an electromagnet must be con-trolled. How can the magnetic field produced by an electromagnet be madestronger or weaker? Think about the components that form an electromag-net. Make a hypothesis about how changing these components would affectthe strength of the electromagnet’s magnetic field.

Real-World QuestionHow can you control the strength of an electromagnet?

Form a HypothesisAs a group, write down the components of anelectromagnet that might affect the strength ofits magnetic field.

Possible Materials22-gauge insulated wire16-penny iron nailaluminum rod or nail0–6 V DC power supply1.5 V “D” cells (3)steel paper clipsmagnetic compassduct tape (to hold “D” cells together)

Goals■ Measure relative strengths of electromagnets.■ Determine which factors affect the strength

of an electromagnet.

Safety Precautions

WARNING: Do not leave the electromagnetconnected for long periods of time because thebattery will run down. Magnets will get hotwith only a few turns of wire. Use caution inhandling them when current is flowing throughthe coil. Do not apply voltages higher than 6 Vto your electromagnets.

Make a Plan1. Write your hypothesis for the best way to

control the magnetic field strength of anelectromagnet.

2. Decide how you will assemble and test theelectromagnets. Which features will youchange to determine the effect on thestrength of the magnetic fields? How manychanges will you need to try? How manyelectromagnets do you need to build?

3. Decide how you are going to test thestrength of your electromagnets. Severalways are possible with the materials listed.Which way would be the most sensitive? Beprepared to change test methods if necessary.

4. Write your plan of investigation. Make sureyour plan tests only one variable at a time.

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Design Your Own

Controlling Electromagnets

Analyze Your Data1. Make a table showing how the strength of your electromagnet depends on changes you made

in its construction or operation.2. Examine the trends shown by your data. Are there any data points which seem out of line?

How can you account for them?

Conclude and Apply1. Describe how the electromagnet’s magnetic-field strength depended on its construction

or operation.

2. Identify the features of the electromagnet’s construction that had the greatest effect on its magnetic-field strength? Which do you think would be easiest to control?

3. Explain how you could use your electromagnet to make a switch. Would it work with both ACand DC?

4. Evaluate whether or not your results support your hypothesis. Why or why not?

Testing ElectromagnetsTrial Electromagnet Construction Features Strength of Electromagnet


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Hands-On Activities

Communicating Your Data

Compare your group’s result with those of other groups. Did any other group use a different method to test the strength of the magnet? Did you get the same results?

Follow Your Plan1. Before you begin to build and test the elec-

tromagnets, make sure your teacherapproves of your plan.

2. Carry out your planned investigation.3. Record your results.

(continued)

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Comparing Magnetic Fields

A magnetic material is made of small regions called magnetic domains. These magneticdomains can be pictured as small bar magnets. When the domains are aligned, as shown in Figure1, the magnetic fields of the domain add together. This causes the material to be surrounded by amagnetic field.

The magnetic field surrounding a magnet exerts a magnetic force on other magnets and magnetic materials. The direction of the magnetic field around a magnet can be represented bymagnetic field lines. Magnetic field lines always begin on the north pole of a magnet and end onthe south pole. Magnetic field lines are closer together where the magnetic field is stronger, and farther apart where the field is weaker.

Figure 1

StrategyYou will observe the effect of a magnetic field around a magnet.You will represent the shape of magnetic field lines by drawing an example.You will compare and contrast the magnetic field lines around a bar magnet and a horseshoe magnet.You will observe the interaction of two magnetic fields.

Materials sheet of clear plasticcardboard framemasking tapeshort bar magnets (2)iron filings in a plastic container with a shaker topsmall horseshoe magnet

ProcedurePart A—Magnetic Field of a Magnet1. Attach the plastic sheet to the cardboard

frame with masking tape.2. Lay one bar magnet on a flat surface with its

north pole at the left. Place the frame overthe magnet so that the magnet is centeredwithin the frame as shown in Figure 2.

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Bar Magnet

S N

Cardboard frame

Plastic sheet

Bar magnet

SN

Figure 2


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Laboratory Activity 1 (continued)

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3. Gently sprinkle iron filings onto the plasticsheet. Observe how the magnetic field ofthe magnet affects the iron filings. The iron filings line up along the magnetic fieldlines around the bar magnet.

4. Sketch the magnetic field lines around thebar magnet in Figure 3 in the Data and Observations section.

5. Remove the lid from the container of theiron filings. Remove the tape holding theplastic sheet to the frame. Carefully lift thesheet and pour the iron filings into thecontainer. Pick up any spilled filings withthe other bar magnet and return them to the container. Replace the lid on thecontainer.

6. Repeat steps 1 through 5 with the horse-shoe magnet. Use Figure 4 in the Data andObservations section to sketch the magneticfield lines around the horseshoe magnet.

Part B—Interaction of Magnetic Fields1. Attach the plastic sheet to the cardboard

frame with masking tape.2. Lay two bar magnets end to end on a flat

surface as shown in Figure 5 in the Data andObservations section. Place the frame overthe magnets so that they are centered withinthe frame.

3. Gently sprinkle iron filings onto the plasticsheet.

4. Sketch the magnetic field lines around thetwo bar magnets in Figure 5 in the Data andObservations section.

5. Remove the plastic sheet and return theiron filings to the container as before.

6. Repeat steps 1 through 5 for each positionof the magnets shown in Figure 6 throughFigure 8 in the Data and Observations section.


Part A—Magnetic Field of a Magnet

Figure 3 Figure 4

Hands-On Activities

SNSN

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Part B—Interaction of Magnetic Fields

Figure 5 Figure 6

Figure 7 Figure 8

SN SN

NS SN SN NS

NS NS


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Questions and Conclusions1. Why were you able to see the magnetic field lines using iron filings?

2. Which has greater strength—the bar magnet or the horseshoe magnet? How do you know?

3. What are the characteristics of the magnetic field surrounding two bar magnets with oppositepoles near each other?

4. What are the characteristics of the magnetic field surrounding two bar magnets with like polesnear each other?

Strategy Check

Can you see the effect of a magnetic field around a magnet?

Can you compare and contrast the magnetic field lines around a bar magnet and a horseshoe magnet?

Can you observe the interaction of two magnetic fields?

Hands-On Activities

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Creating Electromagnets

A magnetic field exists around any wire that carries an electric current. By coiling the wirearound a bolt or nail, the strength of the magnetic field will increase. A coil of wire wrappedaround a bolt or nail will become an electromagnet if the wire is connected to a battery or othersource of current. The magnetic force exerted by an electromagnet can be controlled by changingthe electric current.

StrategyYou will construct several electromagnets.You will compare the strength of the magnetic force of four electromagnets.You will determine the relationship between the strength of the magnetic force and the number of

turns of wire in the coil of the electromagnet.

Materials iron bolts, identical, at least 5 cm long (4)marking penmasking tapeBBs, iron*paper clipssmall, plastic cups (2)insulated wire1.5-V dry cell battery*Alternate materials

Procedure1. Place masking tape on the heads of the

bolts and label the bolts A, B, C, and D.2. Put all the BBs in one cup.3. Test each bolt for magnetic properties by

attempting to pick up some of the BBsfrom the cup. Record your observations inthe Data and Observations section.

4. Wrap 10 full turns of wire around bolt A.Wrap 20 turns of wire around bolt B,30 turns around bolt C, and 40 turnsaround bolt D.

5. Use masking tape to connect the ends ofthe wires of bolt A to the dry cell as shownin the figure. Carefully use your electro-magnet to pick up as many BBs as possible.Hold the electromagnet with the BBs overthe empty cup and disconnect the wire tothe dry cell. Make sure all the BBs fall intothe cup. Count the number of BBs in thecup. Record this value in the table in theData and Observations section.

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Dry cell

Bolt

BBs

Figure 1


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Data and ObservationsObservation of the magnetic properties of the bolts alone:

Hands-On Activities

6. Return all the BBs to the first cup.7. Repeat steps 5 and 6 using bolts B, C, and

D. Record in the table the number of BBseach electromagnet picked up.

8. Use the blank graph in the Data andObservations section to construct a graphrelating the number of BBs picked up bythe electromagnet and the number of turnsof wire in the electromagnet.

Determine which axis should be labeledNumber of BBs picked up and which shouldbe labeled Number of turns of wire. Plotyour findings on the graph.

Electromagnet Number of turns of wire Number of BBs picked up

A

B

C

D

10

20

30

40

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Questions and Conclusions1. How is the number of BBs that were picked related to the magnetic force?

2. How is the strength of the magnetic force exerted by an electromagnet related to the number ofturns of wire?

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3. Explain how your graph supports your answer to question 2.

4. Use your graph to predict how many BBs a bolt wrapped with 50 turns of wire will pick up.

5. Why is it important that the bolts used in this experiment are identical?

6. A magnetic force exists around a single loop of wire carrying an electric current. Explain whycoiling a wire around a piece of iron increases the strength of an electromagnet.

Strategy Check

Can you construct electromagnets of different strengths?

Can you compare the strength of the magnetic force exerted by different electromagnets?

Can you explain how the strength of the magnetic force is related to the number of turnsof wire in the coil of an electromagnet?

Hands-On Activities

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Directions: Use this page to label your Foldable at the beginning of the chapter.

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NS

NS


Meeting IndividualNeeds

Meeting Individual Needs

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OverviewMagnetism and Its Uses

Directions: Circle the term in parentheses that correctly completes the sentence.

1. The north pole of one magnet will be attracted to the (north/south) pole of

another magnet.

2. In an iron nail that is not a magnet, the magnetic domains are

(arranged randomly/aligned).

Directions: Complete the concept map using the terms in the list below.

mechanical energy galvanometers

electrical energy transformers electric motors

Mee

ting

Indi

vidu

al N

eeds

Directed Reading for

Content Mastery

3.

that measure thestrength of

Uses of electromagnetic coils

include

generators

6.

that change

5.

voltage

that increaseor decrease

the

4.

electricalenergy

that change

to

electric current

7.alternatingcurrent

mechanicalenergy

of to

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Section 1 ■ Magnetism

Directions: Use the following terms to complete the crossword puzzle.

north domain opposite like

two magnetic permanent poles

Across2. Type of magnet that keeps its magnetic properties for a long time

4. Group of aligned atoms that behaves like a magnet

5. Number of poles of a horseshoe magnet

6. Type of magnetic poles that attract one another

8. Type of magnetic poles that repel one another

Down1. Type of force that becomes stronger as two magnets are brought closer together

3. Direction a compass needle points

7. Parts of a magnet where the magnetic force is strongest

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Content Mastery

1

2 3

5

4

6 7

8

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Section 2 ■ Electricity and Magnetism

Section 3 ■ Producing ElectricCurrent

Directions: For each of the following, write the letter of the term or phrase that best completes the sentence.1. You can increase the strength of an electromagnet by ______.

a. adding loops to the coil b. reducing the current

2. A transformer that ______ voltage has more loops of wire in its primary coil than in its secondary coil.

a. increases b. decreases

3. An electric fan plugged into a wall outlet runs on ______ current.

a. direct b. alternating

4. The current in an electric motor comes from ______.

a. direction of the current b. amount of current flowing

Directions: Study the following diagram. Then identify each part by filling in each blank below.

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Content Mastery

5. A step-up transformer increases voltage to reduce heat loss.

6. An electric motor uses electrical energy to open a garage door.

7. A generator produces electricity when a coil of wire is rotated in a magnetic field.

8. A step-down transformer decreases voltage for safety reasons.

A

B

C

D

Name Date Class


Key TermsMagnetism and Its Uses

Directions: Match the term in the first column with the definition in the second column by writing the correctletter in the space provided.

1. magnetic domain

2. magnetism

3. magnetic poles

4. galvanometer

5. electric motor

6. electromagnet

7. direct current (DC)

8. transformer

9. electromagnetic induction

10. generator

11. alternating current (AC)

a. temporary magnet made by placing apiece of iron inside a coil of wire thatcarries an electric current

b. device that changes electrical energyinto mechanical energy, such as thatused to turn an electric fan

c. places on a magnet where the magnetic force is the strongest

d. device that increases or decreases thevoltage of alternating current

e. device that uses an electromagnet tomeasure electric current

f. device that produces electric currentby rotating a coil of wire in a magneticfield

g. group of atoms whose magnetic polesare aligned

h. electric current that reverses directionregularly as it flows through a wire

i. properties of magnets and their interactions

j. process of producing an electric current in a loop of wire by eithermoving a magnet through the loop ormoving the loop through a magneticfield

k. electric current that flows only in onedirection through a wire C

opyr

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El magnetismo y sus usos 23

SinopsisEl magnetismo y sus usos

Instrucciones: Haz un círculo alrededor del término que completa correctamente cada oración.

1. El polo norte de un imán será atraído por el polo (norte/sur) de otro

imán.

2. Los dominios magnéticos están (arreglados al azar/alineados) en un clavo dehierro que no haya sido magnetizado.

Instrucciones: Completa el mapa conceptual usando los términos de la siguiente lista.

energía mecánica galvanómetros

energía eléctrica transformadores motores eléctricos

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Dominio del contenido

3.

que miden lafuerza de la

Los usos de los bucleselectromagnéticos

incluyen

generadores

6.

que con-vierten el(la)

5.

voltaje

que aumen-tan o

reducen el

4.

energíaeléctrica

que con-vierten la

en

corriente eléctrica

7.corriente alterna

energía mecánica

de una en

Nombre Fecha Clase

24 El magnetismo y sus usos

Sección 1 ■ El magnetismo

Instrucciones: Usa los siguientes términos para completar el crucigrama.

norte dominio opuesto iguales

dos magnética permanente polos

Horizontales

4. Parte de un imán donde las fuerzas magnéticas son más fuertes

6. Tipo de polos magnéticos que se rechazan

7. Tipo de imán que mantiene sus propiedades magnéticas por mucho tiempo

Verticales

1. Tipo de fuerza que se hace más fuerte cuando dos imanes se acercan uno al otro

2. Grupo de átomos alineados que se comportan como un imán

3. Dirección de la aguja de una brújula

4. Número de polos en un imán en forma de herradura

5. Tipo de polos magnéticos que se atraen Cop

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El magnetismo y sus usos 25

Sección 2 ■ Electricidad y magnetismo

Sección 3 ■ Producción de corriente eléctrica

Instrucciones: Para cada una de las siguientes, escribe la letra del término que complete mejor cada oración.1. Puedes aumentar la potencia de un electroimán al ______.

a. agregar vueltas de alambre b. reducir la corrientea la bobina

2. Un transformador que ______ su voltaje tiene más vueltas de alambreen su primera bobina que en la segunda bobina.a. aumenta b. disminuye

3. Un ventilador eléctrico que se conecta al enchufe de la pared usa corriente ______ .

a. directa b. alterna

4. La corriente de un motor eléctrico proviene de la ______.

a. dirección de la corriente b. cantidad de corriente que fluyeInstrucciones: Estudia el siguiente diagrama. Identifica cada parte llenando los espacios en blanco.

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5. Un transformador elevador aumenta el voltaje para reducir la pérdida de calor.

6. Un motor eléctrico usa energía eléctrica para abrir una puerta.

7. Un generador produce electricidad cuando una bobina de alambre rotadentro de un campo magnético.

8. Un transformador reductor disminuye su voltaje por razones de seguridad.

A

B

C

D

26 El magnetismo y sus usos

Términos clavesEl magnetismo y sus usos

Instrucciones: Coordina cada término de la primera columna con su definición en la segunda columna. Escribela letra correcta en el espacio dado.

1. dominio magnético

2. magnetismo

3. polos magnéticos

4. galvanómetro

5. motor eléctrico

6. electroimán

7. corriente directa (CD)

8. transformador

9. inducción electromagnética

10. generador

11. corriente alterna (CA)

a. imán temporal hecho al colocar untrozo de hierro dentro de una bobinade alambre que transporta una corri-ente eléctrica

b. aparato que cambia la energía eléctricaen energía mecánica, como el que seusa para que gire un ventilador eléc-trico

c. sitios en un imán en donde la fuerzamagnética es más fuerte

d. aparato de aumento o disminuye elvoltaje de la corriente alterna

e. aparato que usa un electroimán paramedir la corriente eléctrica

f. aparato que produce una corrienteeléctrica al rotar una bobina de alam-bre en un campo magnético

g. grupo de átomos cuyos polos mag-néticos están alineados

h. corriente eléctrica que cambia conti-nuamente de dirección al fluir a lolargo de un alambre

i. propiedades de un imán y sus interac-ciones

j. proceso en que se produce una corrienteeléctrica en una bobina de alambre, yasea moviendo un imán a través de labobina o moviendo la bobina a través de un campo magnético

k. corriente eléctrica que fluye solamenteen una dirección en un alambre

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Directions: Complete the diagrams below as indicated and answer the questions.

Figure 1

Magnetism

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1. The lines in Figure 1 show magnetic forces acting between two pairs of bar magnets. Label theunlabeled poles of each magnet with N for north and S for south, between unlike poles.

2. What generalization can you make about the reaction between like poles? Between unlike poles?

3. On Figure 2, draw the lines of force around the bar magnet as they would appear if you sprinkled iron filings around the magnet.

Figure 2

4. Where are most of the iron filings located? Most spread out?

5. What can you infer about the strength of a magnetic field based upon the position of the iron filings?

6. What three materials can be used to make a magnet such as the ones shown above?

S S–– ––

S N


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Electricity and Magnetism

Directions: Circle the term or phrase in parentheses that correctly completes the sentence.

1. When a current is passed through a coil of wire with a piece of iron inside, (an electromagnet,

a commutator) is formed.

2. An electromagnet is a (permanent, temporary) magnet.

3. Adding more turns to the wire coil (increases, decreases) the strength of an electromagnet.

4. Increasing the amount of current that flows through a wire (increases, decreases) the strengthof an electromagnet.

5. Electromagnets change electrical energy into (chemical, mechanical) energy.

6. An instrument that is used to detect current is (an electromagnet, a galvanometer).

7. An electric motor changes (chemical, electrical) energy into mechanical energy.

8. Like a galvanometer, an electric motor contains (a switch, an electromagnet) that is free to

rotate between the poles of a permanent, fixed magnet.

9. A coil’s magnetic field can be flipped by (reversing the direction of current, increasing the

number of loops) in the coil.

10. In a motor, a reversing switch that rotates with an electromagnet is called a (voltmeter,

commutator).

11. In a motor, the stronger the magnetic field in the coil, the (weaker, stronger) the forcebetween the permanent magnet and the electromagnet.

12. The speed of an electric motor can be controlled by varying the amount of (electric current,

mechanical energy) to the motor.

13. Name three devices you see or use everyday that make use of the relationship between electricity and magnetism to operate.


Reinforcement22

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Directions: Study the following diagram. Then label the parts using the correct terms from the list.

electromagnet source of mechanical energy permanent magnet

4. Is this a diagram of a generator or a motor?

Directions: Circle the term in parentheses that makes each statement true.

5. When the wire loop of a (motor, generator) turns, an electric current is produced.

6. The current produced by a generator is (direct, alternating) current.

7. A motor (uses, creates) an electric current as it turns.

8. A device that increases or decreases voltage of electric current passing through a power line is

a (transformer, motor).

9. If the secondary coil of a transformer has more turns than the primary coil, the transformer

is a (step-up, step-down) transformer.

Directions: In the space below, draw a sketch of a step-down transformer that has half as many coils in the secondary coil as in its primary coil. Label the two coils.

10.

Producing Electric Current

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1.

2.

3.


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Magnetic Fields in 2-D and 3-D

The magnetic field surrounding a magnet is actually three-dimensional. You will prepare a permanent two-dimensional model of a magnetic field. This model is similar in appearance towhat you have seen in your textbook. Then, you will prepare two models of magnetic fields inthree dimensions.

Enrichment11


Part A—Preparing a Permanent Two-Dimensional Model of a Magnetic Field

Materials iron filings sheet of white paperbar magnet can of spray shellac

Safety Precautions CAUTION: Keep the shellac away from heatand flames. Use in a well-ventilated room. Weargoggles.

ProcedureSift the iron filings to remove the fine

particles. Use only the larger particles for thisactivity. Place the magnet under the paper andlightly sprinkle the iron filings over the top ofthe paper. Tap the paper gently and the filingsshould move into place, lining up with theforce lines of the magnetic field. In a well-ventilated area, carefully spray the pattern ofiron filings with a light coating of shellac.Allow the shellac to dry completely. The shellac coating should preserve the patternlong enough for you to make comparisonswith the three-dimensional models.

Part B—Preparing a Temporary Three-Dimensional Model of a Magnetic Field

Materials white corn syrup bar magnet

or glycerine stirring rod or spoonlarge jar large test tubeiron filings (sifted) tape or wire (optional)

Safety Precautions CAUTION: Do not taste, eat, or drink anythingused in this experiment. Wear goggles.

ProcedureFill the jar with glycerine or corn syrup. Add

some iron filings and stir gently to distribute

the filings throughout the glycerine. Place thebar magnet in the test tube and stand the testtube straight up in the jar. If needed, use tapeor a piece of wire to hold the tube straight.After a short period of time the filings willalign with the force lines of the magnet. Youwill then be able to see that the magnetic fieldcompletely surrounds the magnet.

Part C—Preparing a Permanent Three-Dimensional Model of a Magnetic Field

Materialspackage of clear gelatin iron filings (sifted)water stirring rod or spoonhot plate large test tubebar magnet tape or wire (optional)large jars

Safety Precautions CAUTION: Do not taste, eat, or drink anythingused in this experiment.

ProcedurePrepare the gelatin as described on the

package. CAUTION: Wear goggles throughoutthe experiment. Pour the prepared gelatin intothe jar. CAUTION: The solution will be hot.After the gelatin starts to thicken, add someiron filings and stir gently to distribute the fil-ings throughout the gelatin. Put the magnet inthe test tube and support the test tube so thatit stands upright in the jar. Place the jar in therefrigerator for several hours. The iron filingswill align with the force lines in the magneticfield and the three-dimensional pattern will bepreserved in the gelatin.

ObservationsDraw a picture of your models on a separatesheet of paper.

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Loudspeakers

The electronic revolution has changedalmost all the components of a stereo system.Receivers, compact disc players, and tape decksare more diverse than they were a few yearsago. However one component that haschanged very little over the years is the loud-speaker, or speaker, as we more typically call it.

A speaker works on the principle that amagnet exerts a force on a current-carryingwire. The electric output of an amplifier isconnected to the wires of the speaker.

The speaker wires are connected internally toa coil of wire. The coil of wire is attached tothe speaker cone. The speaker cone is usuallymade of stiffened cardboard. The cone ismounted so that it can move back and forthfreely. A permanent magnet is mounteddirectly in line with the coil or wire. When thealternating current of an audio signal flowsthrough the wire coil, the coil and theattached speaker cone are affected by the magnetic field of the magnet. The currentalternates at the frequency of the originalaudio signal. The speaker cone moves backand forth at the same frequency, moving theair to produce sound waves.

Each speaker system is made up of individ-ual speakers that have special purposes. Lowerfrequency notes are played through the largestspeaker. This speaker is called the woofer. Awoofer usually has a cone about 20 centimetersin diameter, but it can be larger. It is the largestof the cones because it must move the most airto generate bass frequencies. Mid-range fre-quencies are heard through the midrange cone.The highest frequencies are heard through thesmallest cone, called the tweeter.

Directions: Observe a speaker and answer the following questions.1. Watch the speaker system work when loud music is played through it. What do you observe?

2. Of what type of material are the speaker cones made?

3. When speakers are placed near a television, the picture is sometimes distorted. Why do youthink this might happen?

Enrichment22

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The New Wave in ElectricCurrents

A turbine is an engine with rotators, orblades that spin. When the turbine rotatorspins, electricity is produced. Until recently, thesources of energy that turn the turbine rotatorshave been steam, fossil fuels, or river water.However, many of these sources either arebeing used up or are polluting the environ-ment. The search is on for alternative forms ofenergy to power the turbines.

One form of environmentally friendlyenergy is found in the continuous action ofocean waves and tides. Waves represent a constant movement of energy which couldprovide electricity for large regions of theplanet.

A few countries, like Australia, the UnitedStates, France, and Britain, have had successbuilding stations to harness wave energy, butthe technology is still experimental. Onemajor problem with using waves is that waveenergy produces a back and forth motion andturbines must be built to work continuouslyin one direction. One experimental turbineuses the changes in air pressure produced bywaves flowing into and out of an enclosedspace. The turbine blades have been designedso they turn in the same direction whether theair pressure pushes the blades as the wavecomes in or goes out. The following diagramsshow how this kind of turbine works.

1. Why are ocean waves a promising form of energy to harvest?

2. Why are people searching for new energy sources to use?

3. State one problem with using wave energy as a source of electrical production?

4. How has the problem in question 3 been solved by the prototype discussed here?

Enrichment33


Water

Turbine

Water rushesin, forcing airup the column.The air turnsthe turbine.

When the waterflows back out, theair is pulled backdown and turnsthe turbine.

Air

Water

Turbine

Air

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Section 1 Magnetism

A. Magnetism—the properties and _____________________ of magnets

1. Interaction between two magnets, called magnetic ______________, increases as magnetsmove closer together.

2. A magnetic ______________, which exerts the magnetic force, surrounds a magnet, and

is strongest ________________ to the magnet.

B. Magnetic ______________—the regions of a magnet where the magnetic force exerted by themagnet is strongest

1. All magnets have a ______________ pole and a ______________ pole.

2. Like poles ________________. Unlike poles ______________.

3. Earth has magnetic poles.

a. A compass needle is a small bar magnet that can freely _______________.

b. A compass needle always points ______________.

C. Magnetic materials—_________________, cobalt, and nickel

1. The magnetic field created by each _____________ exerts a force on nearby atoms.

2. Magnetic domains—groups of atoms with ________________ magnetic poles

a. In a magnet, the like poles of all the domains point in the ________________ direction.

b. _________ magnets are made by placing a magnetic material in a strong magnetic field,forcing a large number of magnetic domains to line up.

Section 2 Electricity and Magnetism

A. Moving charges and magnetic fields

1. Moving charges, like those in an electric current, produce _________________ fields.

a. The magnetic ______________ around a current-carrying wire forms a circular patternabout the wire.

b. The direction of the field depends on the __________________ of the current.

c. The _________________ of the magnetic field depends on the amount of current flowing in the wire.

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B. Electromagnet—a __________________ magnet made by placing a piece of iron inside a current-carrying coil of wire

1. Magnetic ______________ is present only when current is flowing in the wire coil.

2. Increase strength of the magnetic field by adding ___________________ to the wire coil or

increasing the __________ passing through the wire.

3. Magnetic properties of electromagnets can be controlled by changing the

_________________________ flowing through the wire coil.

4. Converts electrical energy into ___________________ energy to do work

C. Galvanometer—a device that uses an electromagnet to measure _________________________

D. Electric Motor—a device that changes __________________________ into mechanical energy

1. Contains an electromagnet that is free to _______________ between the poles of a permanent, fixed magnet. The coil in the electromagnet is connected to a source

of _________________________.

2. When a current flows through the electromagnet, a magnetic ______________ is producedin the coil.

3. Changing the __________________ of the current causes the coil in an electric motor tokeep rotating.

4. Rotation ______________ of electric motors can be controlled.

a. Vary the _______________ of current flowing through the coil.

b. When more current flows through the coil, the electromagnet’s magnetic field becomes

_________________, the magnetic force between the coil and the permanent magnet

__________________, and the coil turns _______________.

Section 3 Producing Electric Current

A. From mechanical to electrical energy

1. Electromagnetic induction—the production of an _________________________ by movinga loop of wire through a magnetic field or moving a magnet through a wire loop

2. Generator—a device that produces _________________________ by rotating a coil ofwire in a magnetic field

a. The wire coil is wrapped around an iron core and placed between the poles of a

__________________ magnet.


Note-taking Worksheet (continued)

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b. Coil is rotated by an outside source of ___________________ energy.

c. As the coil turns within the magnetic field of the permanent magnet, an

_________________________ flows through the coil.

d. Direction of the current in the coil in a generator changes ______________ with eachrevolution.

3. Generating electricity

a. Electricity used in the home comes from a ________ _________ with huge generators.

b. Coils of electromagnets in the generators usually connected to a ________________—a large wheel that rotates when pushed by water, wind, or steam.

B. Direct and alternating currents

1. Direct current (DC) is current that flows in _________________ direction through a wire.

2. Alternating current (AC) _________________ the direction of the current flow in a

regular way.

a. In North America, generators produce alternating current at a frequency of

___________ cycles per second, or 60 Hz.

b. A 60-Hz alternating current changes direction ____________ times each second.

C. Transformer—a device that increases or decreases the ________________ of an alternating current

1. Made of ____________ coils (primary and secondary) wrapped around the same iron core.

2. Alternating current in a primary coil creates a changing magnetic field around the iron

core, which induces an alternating current in the __________________ coil.

3. A step-up transformer _____________ voltage. The secondary coil has _____________turns of wire than the primary coil does.

4. A step-down transformer _____________ voltage. The secondary coil has ______________turns of wire than the primary coil does.

5. Power carried in power lines as high as 750,000 V is reduced by _____________ transformers to household current (AC) of 120V.

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Assessment

Assessment

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Chapter Review

Name Date Class


Part A. Vocabulary ReviewDirections: Complete the following sentences using the terms listed below.

magnetism magnetic poles magnetic domains turbine

electromagnet repel commutator generator

electromagnetic induction alternating current direct current

galvanometer transformer electric motor

1. The regions on a magnet where the magnetic force is strongest are called ______.

2. The south pole of a magnet will ______ the south pole of anothermagnet.

3. A device that uses an electromagnet to measure electric current isa(n) ______.

4. A device used to increase or decrease the voltage of current in apower line is a(n) ______.

5. A switch that regularly reverses the current in some motors is a(n) ______.

6. Current that flows in only one direction through a wire is called______.

7. A large wheel that rotates when pushed by water, wind, or steam.

8. When current in a circuit reverses its direction in a regular pattern,it is called ______.

9. The properties and interactions of magnets are referred to as ______.

10. Groups of aligned atoms in a magnet are called ______.

11. A(n) ______ is formed by placing a piece of iron inside a current-carrying coil of wire

12. A machine that changes electrical energy to mechanical energy is a(n) ______ used to do work, such as turning a fan.

13. A device that produces an electric current by rotating a coil of wirein a magnetic field is a(n) ______.

14. The process by which moving a wire through a magnetic field produces an electric current is ______.

Asse

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Chapter Review (continued)


Part B. Concept ReviewDirections: Label the parts of the diagram below. Write your labels on the lines provided. Use the labels permanent magnet, source of mechanical energy, and electromagnet.

Directions: In the spaces provided, identify the function of each device listed below.4. galvanometer

5. step-up transformer

6. electric motor

7. generator

8. electromagnet

9. step-down transformer

10. commutator

Assessment

1.

2.

3.

Transparency Activities


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Section FocusTransparency Activity11


Name Date Class


You might think of magicians when you hear the word levitation,but scientists can levitate, too! This photo shows a magnet levitatingover a ceramic plate. Magnetic levitation has applications rangingfrom advertising displays to high-speed trains.

Magnetic Appeal

1. What happens as you move a magnet closer to a refrigerator door?

2. How do people use magnets in their daily lives?

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Many common household items contain small motors. Some examples are fans, vacuums, and hairdryers. What other appliancesare pictured below?

It Was an Age of Small Appliances

1. Which items use electricity? Which items have motors?

2. Name some ways you have used electric current today.

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Electricity is often generated at power plants by burning fossil fuels.But fossil fuels are nonrenewable resources that, when burned, cancause pollution. There are, however, nonpolluting sources of energy.

Flowing Current

1. What do you think the source of energy is for this hydroelectricpower plant?

2. What do you think would happen if the flow of water through thedam were blocked?

3. What other sources of energy are converted to electric current?

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Teaching TransparencyActivity33 Source of Mechanical

Energy


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Teaching Transparency Activity (continued)

1. How does a generator produce an electric current?

2. With each revolution, how many times does the current change direction?

3. What is electromagnetic induction?

4. What type of energy is used in the transparency to produce the electric current?

5. How is most of the electricity that comes to your school produced?


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AssessmentTransparency Activity

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Directions: Read each question and choose the best answer.


1. According to the graph, what year had the greatest number ofsunspots?A 1948 C 1965B 1958 D 1980

2. These data were collected over a forty-year period. If everythingremains the same, about what year will the number of sunspotsreach another maximum?F 1986 H 1995G 1991 J 1999

3. The graph shows the number of sunspots over a number of years.A reasonable hypothesis based on these data is that the number ofsunspots ___.A does not follow a trend and is totally randomB will never be greater than 200C reaches a maximum about every 11 yearsD will continue to get smaller every year

Sunspot Activity

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Year1945 1950 1955 1960 1965 1970 1975 1980 1985

Documents

Magnetism and Its Uses · Chapter Resources Magnetism and Its Uses ... Teaching Transparency Activity ... Move the magnet at different speeds inside the coil and record the current