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CHAPTER 21 Magnetism
21-1
21-2
21-3
21-4
21-5
21-6
21-7
21-8
21-9
1
What is a magnet?
Lesson Review
2
What causes magnetism?
Lesson Review
3
Human Magnetic Fields
Enrichment Activity for Lesson 21-2
4
How can you make a magnet?
Lesson Review
5
How is Earth like a magnet?
Lesson Review
6
Magnetic Variation
7
How are electricity and magnetism related?
Lesson Review
8
What is an electromagnet?
Lesson Review
9
Electromagnetism
10
What is a transformer?
Lesson Review
11
What is an electric motor?
Lesson Review
12
What is an electric generator?
Lesson Review
13
Generators
14
BIG IDEA Integrating Technology: How does a maglev train work?
Lesson Review
15
THE
Chapter 21 Key Term Review
16
Chapter 21 Test
17
Chapter 21 Answer Key
20
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved.
Magnetism: CHAPTER 21, page 1
Name
Class
Date
21-1 What is a magnet?
Lesson Review
Determine if each item listed will be attracted to a magnet or not affected by a
magnet. Write attracted or not affected in the spaces provided.
____________________ 1. wooden chair
____________________ 2. iron kettle
____________________ 3. paper clip
____________________ 4. milk carton
____________________ 5. glass jar
____________________ 6. refrigerator
____________________ 7. bar of cobalt
____________________ 8. nickel coin
____________________ 9. metal filing cabinet
____________________ 10. window glass
Skill Challenge
Skills: analyzing, diagramming, identifying
Complete the following.
1. Draw two magnets that are repelling each other. Be sure to label the poles of the magnets.
2. Draw two magnets that are attracting each other. Be sure to label the poles of each magnet.
Name
Class
Date
21-2 What causes magnetism?
Lesson Review
Use the diagram to answer the following questions.
1. What do the lines around the magnet represent? _______________________________________________
2. What is the pattern made by the lines called? __________________________________________________
3. Where is this magnet the strongest? __________________________________________________________
4. Where are the lines closest together? __________________________________________________________
5. What do the letters N and S stand for? ________________________________________________________
Skill Challenge
Skills: interpreting diagrams, analyzing
Are the poles of the magnets in the following diagrams attracting or repelling each
other? Write attracting or repelling in the space provided below each diagram.
Then, draw the magnetic lines of force between the poles of each magnet.
Name
Class
Date
Human Magnetic Fields
Skills: inferring, relating
The following passage describes a recent breakthrough in medical technology.
Read the passage. Then, answer the questions.
Organs in the human body have magnetic fields, just as Earth or a horseshoe magnet has
a magnetic field. The most common source of magnetism in the body is electric currents
generated naturally by muscles and nerves. The heart and brain produce the most
current.
New technology has provided better detectors for the tiny magnetic fields produced
by organs. One of the newest and most sensitive detectors is known as SQUID. This
name stands for Superconducting Quantum Interference Device.
Much of the research done with SQUID on human magnetism is centered on the
brain. Electric currents in the brain produce magnetic fields. When these fields are
sensed by SQUID, they produce charts called magnetoencephalograms, or MEGs. The
MEGs sense small sources of activity in the brain. As a result, MEGs can define
individual sources of electrical activity clearly. This can give doctors information to help
diagnose brain disorders. Epilepsy is one illness that is being better diagnosed with the
help of MEGs. A person with epilepsy has disrupted electrical rhythms in the brain.
MEGs help locate the place in the brain that causes the epilepsy.
1. What is the relationship between magnetism and the human body?_______________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
2. Are the magnetic fields produced by the human body large or small? Explain your answer.
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
3. How are electric currents generated in the human body? ________________________________________
____________________________________________________________________________________________
4. What is the relationship between electric currents in the body and magnetism? ____________________
____________________________________________________________________________________________
5. What do the letters SQUID stand for? What does SQUID do? ____________________________________
____________________________________________________________________________________________
6. What are MEGs? What do they show? ________________________________________________________
____________________________________________________________________________________________
Name
Class
Date
21-3 How can you make a magnet?
Lesson Review
Decide if each of the magnets described is a temporary magnet or a permanent
magnet. Write temporary or permanent in the spaces provided.
____________________ 1. lodestone
____________________ 2. magnet made from an iron nail
____________________ 3. nickel magnet
____________________ 4. magnetite
____________________ 5. steel magnet
____________________ 6. soft iron magnet
____________________ 7. cobalt magnet
Skill Challenge
Skills: writing, analyzing
In the space below, write a brief quiz for Lesson 21-3. Your quiz should include
four multiple-choice questions and two short-answer questions. Exchange
quizzes with a classmate. After completing the quiz, return it to your classmate.
Correct your quiz, and explain why you marked any answers incorrect.
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
Name
Class
Date
21-4 How is Earth like a magnet?
Lesson Review
Complete each statement.
1. The ___________________________ traps charged particles from the Sun. When the charged particles
hit particles in the _______________________________ , an ________________________ is produced.
2. The _______________________ of Earth is really like the south pole of a ________________________ .
3. Canada is the location of Earth’s ___________________________________________________ . Earth’s
___________________________________________________ is located near the geographic South Pole.
4. The idea that Earth itself is a _____________________________ was first proposed by William Gilbert.
5. The south magnetic pole is really a ___________________________________________ pole, while the
north magnetic pole is really a ________________________________________________________ pole.
Skill Challenge
Skills: locating, observing
Look at the drawing of Earth. Label the geographic North Pole and South Pole. Then,
label the magnetic south pole and the magnetic north pole. Draw in the magnetosphere.
Name
Class
Date
Magnetic Variation
Skills: interpreting diagrams, applying concepts
The diagram below shows the magnetic and geographic poles of Earth. Use the
diagram to answer the questions.
1. What is the relationship between the location of the geographic North Pole and the
magnetic south pole? ________________________________________________________________________
____________________________________________________________________________________________
2. What is the relationship between the location of the geographic South Pole and
the magnetic north pole? ____________________________________________________________________
____________________________________________________________________________________________
3. When a compass points north, is it pointing more toward the geographic or
magnetic north pole? ________________________________________________________________________
4. The difference between the direction of the geographic North Pole and the
magnetic pole near it is called magnetic variation. Would you expect magnetic
variation to be greater near the North Pole and South Pole, or near the equator? Why? _____________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
Name
Class
Date
21-5 How are electricity and magnetism related?
Lesson Review
Explain how the terms in each of the following pairs are related.
1. electric current, magnetic field _______________________________________________________________
___________________________________________________________________________________________
2. electricity, magnetism _______________________________________________________________________
___________________________________________________________________________________________
3. Michael Faraday, magnets ___________________________________________________________________
___________________________________________________________________________________________
4. electromagnetic induction, electric current ____________________________________________________
___________________________________________________________________________________________
5. Oersted, series circuit _______________________________________________________________________
___________________________________________________________________________________________
Skill Challenge
Skills: experimenting, diagramming
Design an experiment to test Oersted’s discovery. Include the following: a
hypothesis, variables, a procedure, and a type of data to study. In the space
provided, draw a diagram showing what your experimental setup would look like.
Include labels on your diagram.
Name
Class
Date
21-6 What is an electromagnet?
Lesson Review
Decide which is the stronger electromagnet in each figure, A or B. Write your
answers in the spaces provided.
1. __________________
2. __________________
Skill Challenge
Skills: analyzing, modeling
Choose one of the statements listed below. In the space provided, draw a
diagram that illustrates the statement.
1. A coil of wire has a stronger magnetic field than a straight wire.
2. Electromagnets have many important uses.
3. An electromagnet can be made stronger in two different ways.
4. An electromagnet can be turned on and off.
5. The center of an electromagnet is called a core.
Name
Class
Date
Electromagnetism
Skills: analyzing experiments, interpreting data, drawing conclusions
The following experiment was performed by four physical science students. They
wanted to find out what factors affect the ability of an electromagnet to attract
objects. Read the description of the experiment. Then, answer the questions.
Kameko, Justin, Doug, and Elena made an electromagnet by wrapping 50 cm of wire
around a core of five iron nails. Then, they connected the free ends of the wire to the
positive and negative terminals of a dry cell. They tested the electromagnet to see how
many paper clips it would pick up. On their first trial, they found that the magnet would
pick up four paper clips. Then, Kameko wrapped another 50 cm of wire around the
nails. The students found that now their electromagnet picked up six paper clips.
Doug decided to find out what would happen if three of the nails were removed
from the magnet. When the students tried to pick up paper clips, they found that the
electromagnet would pick up only two paper clips. Elena suggested that they replace
the three nails and try increasing the distance between the magnet and the paper clips.
The students found that at first the magnet picked up all six paper clips, but that when
the distance between the magnet and the paper clips was increased by 5 cm, the magnet
picked up only four of the clips. When the distance was increased by another 10 cm, the
magnet picked up only two clips. At a distance of 20 cm from the magnet, no paper clips
were picked up.
1. What was the purpose of this experiment? State the purpose in the form of a question.
____________________________________________________________________________________________
2. What materials did the students use? _________________________________________________________
3. What were the variables in this experiment? ___________________________________________________
____________________________________________________________________________________________
4. State a possible hypothesis for this experiment. ________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
5. What were the results of the experiment? ______________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
6. Based on the results of the experiment, what conclusions can you draw about the
factors that affect the strength of an electromagnet? ____________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
Name
Class
Date
21-7 What is a transformer?
Lesson Review
Write true if the statement is true. If the statement is false, change the underlined
term to make the statement true.
____________________ 1. A transformer uses a current in one wire to induce a current in
a second wire.
____________________ 2. The secondary coil is connected to a source of alternating current.
____________________ 3. A transformer uses alternating current.
____________________ 4. A step-up transformer has more turns in the primary coil than in the
secondary coil.
____________________ 5. A step-down transformer decreases voltage.
____________________ 6. Power companies use step-down transformers to send high-voltage
electricity over long distances.
____________________ 7. A step-down transformer is needed before electricity from an electric
company can be used in people’s homes.
____________________ 8. A current is induced in the secondary coil whenever a switch in the
primary coil is opened or closed.
Skill Challenge
Skills: observing, calculating
Use the diagram to answer the questions. Assume that the voltage change is
proportional to the number of turns in the different coils of wire. For example, a
transformer with three times as many turns on the secondary coil as are on the
primary coil will produce three times as much voltage.
1. If the voltage in the primary coil is 120 volts, how many volts are induced in the secondary coil?
___________________________________________________________________________________________
2. Is this a step-up or a step-down transformer? __________________________________________________
Name
Class
Date
21-8 What is an electric motor?
Lesson Review
Explain how the terms in each pair are related.
1. electrical energy, mechanical energy __________________________________________________________
____________________________________________________________________________________________
2. permanent magnet, electromagnet ____________________________________________________________
____________________________________________________________________________________________
3. attraction, repulsion ________________________________________________________________________
____________________________________________________________________________________________
4. direct current, motor ________________________________________________________________________
____________________________________________________________________________________________
5. poles, electromagnet ________________________________________________________________________
____________________________________________________________________________________________
6. electrical appliances, motors _________________________________________________________________
____________________________________________________________________________________________
Skill Challenge
Skills: analyzing, describing
On a separate sheet of paper, construct a collage that shows how you use
motors in your everyday life. You can cut out pictures of motors from old
magazines. Include at least five pictures. Write a brief paragraph describing how
your life would be different if electric motors had never been invented.
Name
Class
Date
21-9 What is an electric generator?
Lesson Review
Write true if the statement is true. If the statement is false, change the underlined
term to make the statement true.
___________________ 1. A motor converts mechanical energy into electrical energy.
___________________ 2. A current can be induced by spinning a loop of wire inside a
magnetic field.
___________________ 3. An electric generator contains a field and an insulated loop of wire.
___________________ 4. A generator is a large wheel that is turned by water or steam.
___________________ 5. Power plants use small generators.
___________________ 6. When a loop of wire cuts magnetic lines of force, a current is induced
in the wire.
___________________ 7. Steam is produced by burning fuels or from running water.
___________________ 8. The electricity that runs your TV is produced by a motor.
Skill Challenge
Skills: observing, analyzing
Use the diagrams to answer the following questions.
1. What is the source of mechanical energy for the generator in Diagram A? _______________________
2. What is the source of mechanical energy for the generator in Diagram B? _______________________
3. What is the source of mechanical energy for the generator in Diagram C? _______________________
Name
Class
Date
Generators
Skills: interpreting diagrams, labeling, applying concepts
The diagram below shows the operation of a generator. Label the generator,
turbine, and power lines. Then, answer the questions.
1. According to the diagram, what is the source of energy for the generator? In what
form is this energy? _________________________________________________________________________
2. What work does this energy do when it reaches the generator? __________________________________
3. What causes the electromagnets to move? _____________________________________________________
____________________________________________________________________________________________
4. What is the purpose of the coils of wire surrounding the electromagnets? _________________________
____________________________________________________________________________________________
5. How does electricity from a generator such as this one reach your home or school?
____________________________________________________________________________________________
____________________________________________________________________________________________
Name
THE
Class
Big IDEA
Date
Integrating Technology
Chapter 21 How does a maglev train work?
Lesson Review
Refer to the article, call outs, and Figures on pages 474 and 475 of your text to
answer the following questions.
1. What two words is “maglev” short for? _____________________________________________________________
2. Describe how maglev trains float above their tracks. ________________________________________________
____________________________________________________________________________________________________
3. What advantages do maglev trains have compared to regular trains? ________________________________
____________________________________________________________________________________________________
4. What forces are used to pull the cars of a maglev train? _____________________________________________
5. What is a superconducting electromagnet? _________________________________________________________
___________________________________________________________________________________________
6. How fast can a maglev train travel? ________________________________________________________________
Skill Challenge
Skill: inferring
1. What would it be like to travel in a maglev train? ___________________________________________________
____________________________________________________________________________________________________
2. Why do you think that maglev trains are only experimental right now? _____________________________
____________________________________________________________________________________________________
____________________________________________________________________________________________________
3. What might be some disadvantages of maglev trains? _______________________________________________
____________________________________________________________________________________________________
____________________________________________________________________________________________________
Science Log Writing Activity
Complete the Science Log on a separate sheet of paper. To complete the Big Idea Online, go to
www.conceptsandchallenges.com. Follow the online instructions.
Name
Class
Date
Chapter 21 Key Term Review
In the spaces provided, write the term that best fits each description.
Unscramble the letters in brackets [ ___ ] to spell a topic that is discussed in this
chapter. Write the topic in the space provided at the bottom of the page. Then,
explain the meaning of the topic in one or two sentences.
1. Device that changes mechanical energy into electrical energy ___ ___ ___ [ ___ ] ___ ___ ___ ___ ___
2. Process by which a material can be made into a magnet
___ ___ [ ___ ] ___ ___ ___ ___ ___
[ ___ ] ___ ___ ___ ___ ___ ___ ___ ___
3. Temporary magnet made by wrapping a current-carrying wire around an iron core
___ [ ___ ] ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___
4. Force of attraction or repulsion ___ ___ ___ ___ ___ [ ___ ] ___ ___ ___
5. Region of Earth’s magnetic field ___ ___ ___ [ ___ ] ___ ___ ___ [ ___ ] ___ ___ ___ ___ ___
6. Lines that show the shape of a magnetic field
___ [ ___ ] ___ ___ ___ ___ ___ ___
___ ___ ___ [ ___ ] ___
___ ___
___ ___ ___ ___ ___
7. Two ends of a magnet ___ [ ___ ] ___ ___ ___
8. Device that changes electrical energy into mechanical energy
___ ___ ___ ___ ___ [ ___ ] ___ ___
[ ___ ] ___ ___ ___ ___
9. Process by which an electric current is produced by moving a wire in a magnetic field
___ ___ ___ ___ [ ___ ] ___ ___ ___ ___ ___ ___ ___ ___ ___ ___
___ ___ ___ ___ [ ___ ] ___ ___ ___ ___
10. Area around a magnet where magnetic forces can act
___ ___ ___ ___ ___ ___ ___ ___
___ ___ [ ___ ] ___ ___
11. Device that uses electromagnetic induction to increase or decrease the voltage of an alternating
current ___ ___ ___ ___ ___ ___ ___ ___ [ ___ ] ___ ___
Topic: ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___
Explanation: __________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
Name
Class
Date
Chapter 21 Test
Interpreting Diagrams Use the diagrams to answer the following questions.
A
B
1. Which diagram shows an example of a step-up transformer? ____________________________________
2. Which diagram shows an example of repulsion? _______________________________________________
3. Which diagram shows an example of a step-down transformer? _________________________________
4. Which diagram shows an example of attraction? _______________________________________________
Multiple Choice Write the letter of the term or phrase that best completes
each statement.
__________ 1 . T he ma gnetic pole in the Earth’ s S o uthern He misphe re is actua lly a
a. geographic South Pole.
b. geographic North Pole.
c. north pole.
d. south pole.
__________ 2 . T he co il o f a tr a nsfor m e r tha t is a t t a che d t o t he po w e r so ur ce is t he
a. one with more turns.
b. secondary coil.
c. one with fewer turns.
d. primary coil.
__________ 3 . Electricity ne ede d to run applia nce s usua lly co me s o rigina lly fro m a
a. motor. b. magnet. c. generator. d. battery.
__________ 4 . M a gne t ism is a fo r ce o f
a. gravity. b. weight. c. voltage.
d. attraction or repulsion.
__________ 5. The magnetic lines of force are closest together at a magnet's
a. poles. b. north pole. c. south pole. d. middle.
Name
Class
Date
Chapter 21 Test (continued)
__________ 6 . An e le ct ric a pplia nce ne e ds a m o to r t o cha nge e le ctr ica l e ne r gy int o
a. heat energy. b. mechanical energy. c. chemical energy. d. light energy.
__________ 7 . T he scie nt ist who disco ve r ed t ha t a n e le ct r ic cur r ent ca use s a m a gne tic field w a s
a. Joseph Henry.
b. Michael Faraday.
c. Hans Christian Oersted.
d. Thomas Edison.
__________ 8. An electromagnet is
a. a permanent magnet.
c. an alnico magnet.
b. a temporary magnet.
d. a weak magnet.
__________ 9. An example of a natural magnet is
a. iron. b. aluminum. c. nickel.
d. lodestone.
__________ 10. Of the following examples, the one that will make an electromagnet with the strongest
magnetic field is a
a. wire with four coils.
b. straight wire.
c. wire with three coils. d. wire with two coils.
__________ 11. Of the following items, the one that would be attracted to a magnet is
a. an iron bar. b. a glass jar. c. a wooden toothpick. d. a plastic cup.
__________ 12. When a material, such as an iron nail, is made into a magnet, magnetism has been
a. destroyed. b. strengthened. c. weakened. d. induced.
__________ 13. Temporary magnets are
a. easy to magnetize.
c. always weak magnets.
b. hard to magnetize.
d. always strong magnets.
__________ 14. The British scientist who stated that Earth is similar to a bar magnet was
a. Nikola Tesla.
b. Isaac Newton.
c. William Gilbert.
d. Michael Faraday.
__________ 15. The northern and southern lights can also be called
a. auroras. b. magnetospheres. c. magnetic lights.
d. solar winds.
__________ 16. A transformer that has more turns in the primary coil than in the secondary coil is an
example of a
a. step-up transformer.
b. step-down transformer.
c. secondary transformer.
d. primary transformer.
__________ 17. A device that changes mechanical energy into electrical energy is called a
a. motor. b. turbine. c. generator. d. transformer.
Name
Class
Date
Chapter 21 Test (continued)
Written Response Answer the following questions in complete sentences.
18. EXPLAIN: How are electricity and magnetism related?__________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
19. INFER: How do you think the discovery of the relationship between electricity and
magnetism has affected modern society? ______________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
Answer Key
CHAPTER 21: MAGNETISM
21-1 What is a magnet?
Lesson Review
1. not affected 2. attracted 3. attracted 4. not
affected 5. not affected 6. attracted 7. attracted
8. attracted 9. attracted 10. not affected
Skill Challenge
1.
2.
21-3 How can you make a magnet?
Lesson Review
1. permanent 2. temporary 3. temporary
4. permanent 5. permanent 6. temporary
7. temporary
Skill Challenge
A possible sample quiz:
1. The process by which a material can be made into
a magnet is called: A. magnetic naturalization
B. Magnetic induction C. Magnetic temporization
D. Magnetic perspiration (Answer: B)
2. Of the following metals, the hardest to magnetize
is: A. iron B. nickel C. cobalt D. steel
(Answer: D)
3. When materials are magnetized the: A. domains
are made to point in the same direction. B. atoms
are made to be positive. C. atoms are made to be
negative. D. atoms are neutralized. (Answer: A)
Lesson Review
1. lines of force 2. a magnetic field 3. at the poles
4. at the poles 5. north pole and south pole
Skill Challenge
1. attracting 2. repelling 3. repelling
Check students’ drawings for lines of force.
Enrichment Activity: Human Magnetic Fields
1. Organs in the human body have magnetic fields.
The most common source is electric currents
generated by muscles and nerves. 2. They are
extremely small. Very sensitive instruments are
needed to detect them. If they were larger, ordinary
magnets could detect them. 3. Electric currents are
generated by muscles and nerves. The heart and the
brain produce the most current. 4. Electric currents
generated in the brain and other parts of the body
produce magnetic fields. 5. Superconducting
Quantum Interference Device; this device detects
magnetic fields produced by human organs.
6. magnetoencephalograms; a chart that shows
magnetic fields produced by electric currents in the
brain
4. Materials that are hard to magnetize but keep
their magnetism are called: A. permanent magnets.
B. temporary magnets. C. rubbed magnets.
D. field magnets. (Answer: A)
5. What happens internally to materials that are
magnetized? (Answer: Inside the materials, the
domains of the materials are made to point in the
same direction.)
6. How can a material lose its magnetism?
(Answer: A magnet can be dropped and lose its
magnetism. It can also lose its magnetism through
being heated.)
Answer Key
Lesson Review
1. magnetosphere, atmosphere, aurora 2. north
magnetic pole, magnet 3. south magnetic pole,
north magnetic pole 4. magnet 5. north, south
Skill Challenge
21-5 How are electricity and magnetism
related?
Lesson Review
1. An electric current produces a magnetic field.
2. When a magnetic compass is near an electrical
device, the pointer may no longer point north. The
relationship is called electromagnetism. 3. Michael
Faraday did experiments with magnets to find out if
a magnetic field produced an electric current. 4. In
electromagnetic induction, an electric current is
produced by moving a wire in a magnetic field or by
moving a magnet past a stationary wire. 5. Oersted
used a series circuit to discover that an electric
current produces a magnetic field.
Skill Challenge
Enrichment Activity: Magnetic Variation
1. They are both high in the Northern Hemisphere,
but they are about 1,300 k away from each other.
2. They are both in the Southern Hemisphere, but
they are not in exactly the same place. 3. the
geographic North Pole 4. near the poles, because
the angle between the line connecting the
geographic poles and the line connecting the
magnetic poles gets larger as one moves closer to the
poles
Possible answers: Hypothesis: An electric current
produces a magnetic field around a wire, affecting a
compass needle held nearby. Variables: The
amount of electricity running through the wire, and
the distance between the compass needle and the
wire. Procedure: First, connect the battery to the
wire and to the switch. Next, flip the switch, causing
an electric current to flow through the wire. Move
the compass needle close to the wire, see if the
needle responds to the magnetic field. Continuing to
hold the compass needle near the wire, turn off the
switch. Observe the compass needle. Type of data
to study: I will record my observations about what
the compass needle does when it is near the wire,
and the differences in the compass needle when
current is flowing through the wire and when there
is no current flowing.
Answer Key
21-7 What is a transformer?
Lesson Review
1. B 2. B
Skill Challenge
Check students’ diagrams to be sure that they agree
with the statement they chose. Possible answers: 1. a
coil of wire picking up lots of iron nails beside a
straight wire not picking up any 2. a picture of a
radio, a telephone, and a computer 3. an
electromagnet with very few coils picking up very
few nails, next to an electromagnet with lots of coils
picking up lots of nails; an electromagnet with a
wire labeled weaker current picking up very few nails
with an electromagnet labeled strong current picking
up lots of nails 4. an electromagnet hooked to a
switch labeled on and off with the switch turned to
on, and the electromagnet picking up lots of nails;
next to it the same electromagnet, but with the
switch turned to off above the nails but not picking
them up 5. a picture of an electromagnet made of
wire wrapped around an iron nail with a line
pointing to the nail labeled core
Lesson Review
1. true 2. primary 3. true 4. fewer 5. true
6. step-up 7. true 8. true
Skill Challenge
1. 240 volts 2. step-up transformer
Enrichment Activity: Electromagnetism
1. What factors affect the strength of an
electromagnet? 2. dry cell, 5 iron nails, wire, and
paper clips 3. number of loops of wire; size of core
(number of nails); and distance between magnet and
paper clips 4. The strength of an electromagnet is
affected by the number of loops of wire, the size of
the magnet, and the distance between the magnet
and the object being pulled. 5. The magnet picked
up more paper clips when the number of loops of
wire was increased. It picked up fewer paper clips
when the number of nails in the magnet was
decreased. It picked up fewer paper clips as the
distance between the magnet and the paper clips
increased. 6. The strength of an electromagnet
increases with the number of loops of wire, and
decreases as the size of the magnet core decreases.
The effectiveness of the magnetic field decreases as
the distance between the magnet and the object
being pulled increases.
21-8 What is an electric motor?
Lesson Review
Possible answers: 1. An electric motor changes
electrical energy into mechanical energy. 2. An
electric motor uses both a permanent magnet and an
electromagnet. 3. Attraction and repulsion between
an electromagnet and a permanent magnet are
responsible for the motion of an electric motor.
4. Direct current cannot be used in an electric motor
unless a special switch called a commutator is used.
5. You can reverse the poles of an electromagnet by
reversing the direction of the current running
through it. 6. Many electrical appliances use electric
motors.
Skill Challenge
Check students’ collages. Possible pictures: electric
appliances such as dishwashers, blenders, electric
ovens, air conditioners, electric tools, and
refrigerators
Sample paragraph: My life would be different if
electric motors had never been invented. The electric
motor is one of the main ways in which power
plants produce electricity. Without the electric
motor, most of the appliances that we use every day,
from blenders to blow dryers, would not exist.
Lesson Review
1. generator 2. true 3. magnet 4. turbine 5. large
6. true 7. nuclear energy 8. generator
Skill Challenge
1. wind 2. waterfall 3. steam
Answer Key
Enrichment Activity: Generators
A. power lines B. generator C. turbine 1. moving
water; mechanical energy 2. spins the turbine
3. the spinning of the turbine, which in turn spins
the magnets 4. As the electromagnets move, the
wire cuts magnetic lines of force, producing an
electric current. 5. The electric current produced in
the wires is conducted to power lines that eventually
reach homes, schools, and other buildings.
The Big Idea
Lesson Review
1. magnetic levitation 2. Maglev trains have
magnets on the bottom of the train that are repelled
by magnets on the tracks below. Because of this, the
train floats above the track. 3. The advantage is that
maglev trains have almost no friction as they are
gliding above the track. Because of this, they use less
fuel than ordinary trains, which means less pollution
will be produced. 4. magnetic force 5. an
electromagnet that is supercooled so electricity flows
through it with almost no resistance 6. about 500
km per hour
Skill Challenge
1. It would probably be a much smoother, quieter,
and faster ride than on an ordinary train. 2. Maglev
trains are a new idea, and there are several possible
designs for them. Before they become commonplace,
engineers need to decide what the best design is. In
addition, maglev trains are expensive to build.
3. Possible answers: the large cost associated with
building a maglev train; The lack of friction in a
train might make it harder to stop the train. The fact
that the trains go so fast might make them more
dangerous in an accident.
Chapter Test
Interpreting Diagrams
l. A 2. C 3. B 4. D
Multiple Choice
1. c 2. d 3. c 4. d 5. a 6. b 7. c 8. b 9. d 10. a
11. a 12. d 13. a 14. c 15. a 16. b 17. c
Written Response
18. Electricity and magnetism are two aspects of the
same force. An electric current produces a magnetic
field around the wire through which it is running. A
moving magnetic field produces a current in a wire
through which the field moves.
19. The ability of scientists to use magnetic fields to
produce electricity, as it is in generators, has made
power plants possible. It has established another
source of electricity besides batteries and lightning,
allowing engineers to convert mechanical energy
into electrical energy. It has also allowed for the
invention of the electric motor, which is responsible
for our ability to convert the electricity from a power
plant back into mechanical energy.
Key Term Review
1. generator 2. magnetic induction
3. electromagnet 4. magnetism 5. magnetosphere
6. magnetic lines of force 7. poles 8. electric motor
9. electromagnetic induction 10. magnetic field
11. transformer
Topic: electromagnetism
Explanation: Electromagnetism is the relationship
between magnetism and electricity.

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