Module 20: Magnetism
Performance Expectations
Students will explore content and develop skills related to the following Performance Expectations.
Mastery can be assessed using the associated online Applying Practices activities.
Build to Performance Expectations
HS-PS2-5. Plan and conduct an investigation to provide evidence that an electric current can
produce a magnetic field and that a changing magnetic field can produce an electric current.
(Mastery in Module 21)
Master Performance Expectations
HS-PS3-5. Develop and use a model of two objects interacting through electric or magnetic fields to
illustrate the forces between objects and the changes in energy of the objects due to the interaction.
Assess this PE using Applying Practices: Modeling Magnetic Fields (Lesson 1)
Science and Engineering Practices
Developing and Using Models
Disciplinary Core Ideas
PS3.C: Relationship Between Energy and
Forces
ELA/Literacy Connections WHST.9-12.7, WHST.11-12.8,
WHST.9-12.9, SL.11-12.5
Crosscutting Concepts
Cause and Effect
Math Connections MP.2, MP.4
Expand on Performance Expectations
S-PS3-2. Develop and use models to illustrate that energy at the macroscopic scale can be
H
accounted for as a combination of energy associated with the motion of particles (objects) and
energy associated with the relative position of particles (objects). (Mastered in Module 11,
Module 19)
S-PS3-3. Design, build, and refine a device that works within given constraints to convert one
H
form of energy into another form of energy.* (Mastered in Module 10)
Module 20 • Magnetism
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Module Planner
GO ONLINE to curate your presentations, interactive content, additional resources, and
media library, and find answer keys, materials lists, rubrics, differentiated instruction, and more.
Module Resources
Pacing
(min)
CER
Module
Launch
Lesson
1
Lesson
2
Module
Close
45
45
90
45
Encounter the
Phenomenon
Collect Evidence
Collect Evidence
LL: Direction of Magnetic
Fields
QI: 3-D Magnetic Fields;
Magnetic Domains
Go Further: Data Analysis
Lab
Claim, Evidence,
Make Your Claim
Reasoning
Labs and
Investigations
Revisit the Phenomenon
VI: Charge in a Magnetic
Field
PhysicsLAB: Current and
Field Strength; Make an
Electromagnet
PhET Simulation:
Magnets and
Electromagnets
Media and OER
PT: Force on a Charged
Particle
Beyond the Classroom:
Google Expedition
Lesson Check
Lesson Check
Assess
Module Vocabulary
Practice
Module Test
Modeling Magnetic Fields
HS-PS3-5
Applying Practices
for NGSS
KEY:
LL: Launch Lab
QI: Quick Investigation
Standard Module Resources
VI: Virtual Investigation
•
Interactive Content
•
Science Notebook
•
Math Handbook
•
Teacher Presentation
(PowerPoint™)
•
Selected Solutions
•
•
LearnSmart™
Science and Engineering
Practices Handbook
545B
Module 20 • Magnetism
PT: Personal Tutor
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Module 20: Magnetism
Module Storyline
MODULE 20
In this module, students will seek to answer the Encounter
the Phenomenon Question “What makes this electromagnet stronger than a typical refrigerator magnet?” The
lessons in this module each provide part of the answer to
this question.
MAGNETISM
•
Lesson 1: Understanding Magnetism
Students will explore the properties of magnets,
magnetic domains, magnetic fields, and
electromagnets. This will lead them to understand
refrigerator magnets are made of magnetized iron that
contains magnetic domains, while electromagnets use
electric currents to produce magnetic fields.
•
Lesson 2: Applying Magnetic Forces
Students will explore the effects of magnetic forces on
current-carrying wires and moving charged particles,
as well as related applications, such as galvanometers
and motors. This will lead them to understand that
magnetic fields affect not just magnets and magnetic
materials but moving charged particles as well.
Stockbyte/Getty Images
ENCOUNTER THE PHENOMENON
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PRESENTATION
Teacher Presentation:
Magnetism
INTERACTIVE CONTENT
Chapter: 20
10:38PM
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INTERACTIVE CONTENT
Encounter the Phenomenon:
Magnetism
Have students read the Encounter the Phenomenon
­question and study the module opener photo.
Then, have students watch the video either as a class,
in groups, or individually.
Ask Questions
Asking Questions and Defining Problems
Have students revisit the Driving Question Board and
review the Unit question. Then, add the Module title and
the Encounter the Phenomenon Question. Have students
identify the sticky note questions they think will be
answered in this Module and place them under the Module
Encounter the Phenomenon Question. Students may also
have additional questions about the Module Phenomenon
to add to the board.
Video Supplied by BBC Worldwide Learning
CER: Magnetism
Module 20 • Magnetism
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Module 20: Encounter the Phenomenon
O
btaining, Evaluating, and
Communicating Information
Make Your Claim
A scientific claim answers a question or offers a solution
to a problem. Give students time to reflect and brainstorm,
then have each student take a clear stand and write a
claim in their CER charts.
MODULE 20
MAGNETIC FIELDS
ENCOUNTER THE PHENOMENON
What makes this electromagnet
stronger than a typical
refrigerator magnet?
GO ONLINE to play a video about
the discovery of the connection between
electricity and magnetism.
Collect Evidence
After students have made a claim, they are ready to collect
evidence. Research, experimentation, or data interpretation
are common sources of scientific evidence.
The online Launch Lab Direction of Magnetic Fields
can be used at this time as a starting point for investigation.
At the end of each reading or activity, students should
record their evidence in the class Summary Table.
Ask Questions
Do you have other questions about the phenomenon? If so, add them to the driving
question board.
CER
Claim, Evidence, Reasoning
Make Your Claim Use your
CER chart to make a claim
about why the electromagnet
is stronger than a refrigerator
magnet. Explain your
reasoning.
Collect Evidence Use the
lessons in this module to
collect evidence to support
your claim. Record your
evidence as you move
through the module.
Explain Your Reasoning You
will revisit your claim and
explain your reasoning at the
end of the module.
GO ONLINE to access your CER chart and explore resources that
can help you collect evidence.
LESSON 1: Explore & Explain:
Magnetic Domains
546
LESSON 2: Explore & Explain:
Forces on Current-Carrying Wires
Additional Resources
(t)Video Supplied by BBC Worldwide Learning; (bl)Richard Hutchings/Digital Light Source; (br)McGraw-Hill Education
Claim, Evidence, Reasoning
Module 20 • Encounter the Phenomenon
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Chapter: 20
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Teacher Toolbox
Identifying Preconceptions
The following preconceptions will be addressed at point
of use.
Lesson 2
• A magnetic field produces a force on a current even
when it is parallel to the magnetic field.
546
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Lesson 1: Understanding Magnetism
Types of Interactions
Properties of Magnets
PS2.B Forces at a distance are explained by fields
(gravitational, electric, and magnetic) permeating
space that can transfer energy through space.
Magnets or electric currents cause magnetic fields;
electric charges or changing magnetic fields cause
electric fields.
Magnets have been known and used for more than 2000 years. Ancient sailors used naturally
magnetic rocks, called lodestones, as compasses. Ancient physicians thought lodestones could
cure disease. Today, many objects we use every day rely on magnets to work. Electric motors,
earbuds, loudspeakers, and computer hard drives all depend on the interaction between magnetic
fields and electric currents.
*Bold font indicates the part of the DCI covered in
this lesson.
LESSON 1
UNDERSTANDING MAGNETISM
FOCUS QUESTION
Why are some materials magnetic and others are not?
Poles of magnets As a child, you likely did investigations with simple magnets, such as
those shown in Figure 1. You probably noticed that the two ends of a magnet behave in different
ways. That is because magnets are polarized: they have two opposite ends, called poles.
Engage
Richard Hutchings/Digital Light Source
Launch the Lesson Interactive Content can be assigned
the night before class as a lesson preview, during class
to spark discussion, as a resource during inquiry, or as
homework.
Driving Question Board
DC
SEP
Figure 1 All magnets, no matter their
size or shape, have two poles.
I
CCC
3D THINKING
Disciplinary Core Ideas
COLLECT EVIDENCE
Use your Science Journal to
record the evidence you collect as
you complete the readings and
activities in this lesson.
Crosscutting Concepts
Science & Engineering Practices
INVESTIGATE
GO ONLINE to find these activities and more resources.
Applying Practices: Modeling Magnetic Fields
HS-PS3-5. Develop and use a model of two objects interacting through electric or magnetic
fields to illustrate the forces between objects and the changes in energy of the objects due
to the interaction.
Lesson 1 • Understanding Magnetism
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PRESENTATION
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INTERACTIVE CONTENT
Launch the Lesson:
Understanding Magnetism
Explore and Explain
Science Journal Remind students to keep records of
their investigations in their Science Journals. Additionally,
be sure that each reading or activity is added to the
class Summary table.
Three-Dimensional Thinking The activities called out
in the Student Edition will allow students to practice
three-dimensional thinking. Worksheets for these activities
can be found online.
DC
SEP
Teacher Presentation:
Understanding Magnetism
Chapter: 20
08:57PM
Have students revisit the DQB to remind themselves of the
Unit and Module questions. Have them identify the sticky
note questions they think will be answered in this lesson.
Then, have students read the Focus Question and add it
to the DQB. Students will revisit the Focus Question at the
end of the lesson.
I
CCC
IMPLEMENTATION OPTIONS
Presentation: Teacher-Facilitated Pathway
neal and molly jansen/Alamy
Use the Teacher Presentation to support classroom
instruction and spark discourse. Obtain data to
inform your instruction by assigning the Interactive
Content, Additional Resources, and Assessment.
Interactive Content: Student-Led Pathway
Students can use the online Interactive Content,
along with the Student Edition, Science Notebook,
projects, and labs, to collect evidence to support
their claim. They can record their evidence in their
Science Journals and the class Summary Table.
Tie to Prior Knowledge
Fields and Electric Current The module on gravitation
introduced the concept of fields, and students studied this
concept again in the module on electric fields. This module
introduces magnetic fields to help explain attraction and
repulsion between magnets.
Reinforcement
Mutual Forces Remind students that interactions always
come in pairs. For example, if one pole exerts a force on
a second pole, the second pole exerts a force of equal
strength that pushes the first pole in the opposite direction.
This is another example of Newton’s third law.
Lesson 1 • Understanding Magnetism
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Lesson 1: Understanding Magnetism
Quick Demo
Magnetic Repulsion
Materials pencil, two disk magnets
Procedure Hold a pencil vertically. Slide the disk m
­ agnets
onto the pencil with like poles facing each other. The top
magnet will float above the bottom magnet. Ask students
what keeps the upper magnet floating. M
­ agnetic repulsion between the two like poles pushes the two magnets
apart. The upper magnet floats in a position where the
magnetic force from the bottom magnet ­balances the
gravitational force from Earth. Ask students what determines the size of the gap. gravity and the strength of the
magnets
Est. time: 5 min
Figure 2 Like poles of two magnets repel each other
(top), while unlike poles attract each other (bottom).
Like poles repel.
Unlike poles attract.
Think about a bar magnet suspended on a string. In what direction do you think it will point
when it comes to rest? A magnet that is free to rotate always comes to rest pointing in the
north-south direction. The pole pointing north is called the north-seeking pole or, more simply,
the north pole. The opposite pole is the south pole. A compass is just a small magnet, mounted
so that it is free to rotate.
Earth as a magnet The needle of a compass points in a north-south direction because Earth
itself is a giant magnet. A compass’s north pole points to Earth’s geographic North Pole. As you
will read, however, a magnet’s north pole is always attracted to a magnetic south pole. Therefore,
what we call the North Pole is actually near Earth’s magnetic south pole, and the South Pole is
near Earth’s magnetic north pole.
Get It?
Describe examples of how humans have used Earth’s magnetic poles through the
centuries.
Reluctance in Magnetic Circuits A magnetic circuit is the
closed path described by magnetic flux. Reluctance (magnetic) is analogous to resistance (electric) in that reluctance
is a measure of the opposition to magnetic flux offered by a
magnetic circuit. A magnetic circuit with reluctance is analogous to an electric circuit with resistance: flux, reluctance,
and magnetomotive force are analogous to electric current, resistance, and electromotive force. Use resistance in
an electric circuit to help students understand reluctance
in a magnetic circuit. As resistance goes up, current goes
down and as reluctance goes up, magnetic field strength
goes down.
Get It?
Ancient sailors used magnetic poles as compasses
and ancient physicians thought that magnetic rocks, or
­lodestones, could cure disease.
Opposite poles What’s inside a magnet that makes it polarized? You know that when you
bring a metal rod near an electric charge, one end of the rod becomes negatively charged and the
other end becomes positively charged, polarizing the rod. You might think a magnet, like the
ones shown in Figure 2, is similar, with one half of the magnet positive and the other half negative, but this is not the case. No matter how you cut or break a magnet, a magnet always has two
poles. There have been many searches for objects, called monopoles, with only a north pole or
only a south pole, but no monopole has ever been found.
SCIENCE USAGE v. COMMON USAGE
Polarized
Richard Hutchings/Digital Light Source
Use an Analogy
Science usage: having two opposite ends
All magnets are polarized.
Common usage: broken into opposing factions or groups
Members of Congress were polarized on the issue of Social Security reform.
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INTERACTIVE CONTENT
Explore and Explain: Poles
of Magnets
Activity
van_yog/Shutterstock
Magnetized Steel Students might believe that all steel
alloys can be magnetized. You can have students test this
belief by placing a long stainless steel bolt or screw in
­contact with the north pole of a permanent magnet. You
can test to see whether the other end is acting as a magnetic pole by trying to pick up iron filings. Some stainless
alloys are magnetic, albeit more weakly magnetic than
other steels. Test different items and let students observe
the differences.
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Module 20 • Magnetism
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Quick Demo
Creating a Magnet
Materials pistol-type soldering gun, screwdriver, permanent magnet, small metal objects such as pins
Poles repel or attract You have likely noticed that forces between two
magnets differ depending on how you orient the magnets. When you place the
north pole of one magnet next to the north pole of another magnet, the magnets
repel each other, as they do in the top of Figure 2. The same is true when you
bring two south poles together. If, however, you brought the north pole of one
magnet next to the south pole of another magnet, the poles would attract each
other, as they do in the bottom of Figure 2. Like poles repel; unlike poles attract.
Temporary magnets
Magnets also attract nails, paper clips, tacks, and
other metal objects. These objects have no poles, and both the north and south
poles of a magnet attract them. When a magnet touches one of these objects,
such as the nail in Figure 3, the magnet polarizes the object, making it a
temporary magnet. This process is called magnetization by induction.
You can use a pistol-type soldering gun to illustrate
demagnetization. Magnetize a screwdriver by stroking it
with a permanent magnet. Show students that it can pick
up small metal objects such as pins. Now ­demagnetize
the screwdriver blade as follows: Squeeze and hold the
soldering-gun trigger and insert the blade between the
wires that hold the tip. Withdraw the blade before releasing the trigger. The screwdriver will no longer attract
metal objects because its magnetic domains are now
randomly arranged.
Figure 3 A common nail attached to a
magnet becomes a temporary magnet by
induction.
Identify the north and south poles of the
nail.
Magnets only attract some metals. Brass, copper, and aluminum are common
metals that are not attracted to magnets. Iron, nickel, and cobalt are strongly
attracted. Materials containing these elements, called ferromagnetic materials,
can become temporary magnets. A steel nail can become a temporary magnet
because it is made of iron with tiny amounts of carbon and other materials. When
you remove a nail from a magnet, the nail gradually loses most of its magnetism.
Magnetic domains What gives a permanent or temporary magnet its
magnetic properties? Each atom in a ferromagnetic material acts like a tiny
magnet; each has two poles. Each is part of a domain, which is a group of
neighboring atoms whose poles are aligned. Look at the arrows in Figure 4. Each
arrow represents a domain. Although domains can contain as many as 1020
individual atoms, they are tiny—usually from 10 to 1000 microns across. Even a
small sample of a ferromagnetic material contains a huge number of domains.
Richard Hutchings/Digital Light Source
In a ferromagnetic material that is not magnetized, each domain points in a
random direction, as shown in the top panel of Figure 4. But if the ferromagnetic
material is next to a strong magnet, most of the object’s domains preferentially
align to point in the same direction as the poles of the external magnet, as shown
in the bottom panel of Figure 4. When its domains are aligned in the same
direction, the material becomes a temporary magnet. When an external magnet is
removed from a temporary magnet, the domains of the temporary magnet return
to a random arrangement, and the material loses its magnetization. How long it
takes for a temporary magnet to lose its magnetization depends on the
interactions between the atoms, which depend on the microscopic structure of
the material.
Creating permanent magnets The only naturally occurring magnet is
the mineral magnetite. The lodestones that ancient sailors used were nothing
more than pieces of magnetite. If magnetite is the only naturally occurring
magnet, how, then, are commercial permanent magnets made?
Nonmagnetized Material
Est. time: 5 min.
Magnetized Material
Figure 4 Domains in a nonmagnetized
ferromagnetic material point in random
directions (top). When a strong magnet
is placed near a ferromagnetic material,
the domains in that ferromagnetic
material align with those of the external
magnet (bottom).
Get It?
Cite Evidence Infer what the magnetic domains look like in the magnet
shown on the first page of this module.
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Get It?
The magnetic domains are aligned with the strong magnet
hanging from above.
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Caption Question Fig. 3: The head of the nail is its north
pole because it is attracted to the magnet’s south pole.
12:12PM
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INTERACTIVE CONTENT
Explore and Explain:
Magnetic Domains
EL Support
ELD PII.11/12.2a
EMERGING LEVEL Draw students’ attention to
Richard Hutchings/Digital Light Source
These objects in the Temporary Magnets paragraph.
Support students in recognizing that These objects
refers to nails, paper clips, tacks and other metal
objects. Demonstrate moving your finger from These
objects back to the list of objects in the previous
sentence.
EXPANDING LEVEL Draw students’ attention to These
objects in the Temporary Magnets paragraph. Ask: Do
you know what These objects are? Guide students to
recognize what These objects refers to. With students,
restate the sentence replacing These objects with what
the phrase refers to.
BRIDGING LEVEL Draw students’ attention to These
objects in the Temporary magnets paragraph. Elicit what
These objects refers to. Have students look for another
similar referent in the same paragraph This process
and discuss what it refers to. the magnet polarizing
the object
Lesson 1 • Understanding Magnetism
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Lesson 1: Understanding Magnetism
PRACTICE Problems
Reinforcement
Induced Polarity Have students reflect on what they
know about induced charges. Refer them to the module
about static electricity. Ask students to predict the induced
­polarity of a metal object as it is brought near a pole of
a permanent magnet. The end of the metal object that is
closest to the pole of the permanent magnet becomes an
opposite pole because opposite poles attract.
Quick Demo
Induced Polarity
Materials compass, permanent magnet with the poles
identified, two nails
Procedure Place the head of one of the nails into contact with the north pole of the permanent magnet. Place
the opposite end of the other nail in contact with the
north pole of the permanent magnet. Test the polarity of
both nails using the compass. Discuss induced polarity.
Ask students if the nail will stay magnetized when removed from the permanent magnet. The nail will only be
­magnetized while in contact with the permanent magnet.
PRACTICE Problems
ADDITIONAL PRACTICE
1. If you hold a bar magnet in each hand and bring your hands close together,
will the force be attractive or repulsive if the magnets are held in the
following ways?
a. The two north poles are brought close together.
b. A north pole and a south pole are brought together.
2. Figure 5 (at left) shows five disk magnets floating above one another. The
north pole of the top-most disk faces up. Which poles are on the top side of
each of the other magnets?
3. The ends of a compass needle are marked N and S. How would you explain
to someone why the pole marked N points north? A complete answer should
involve Earth’s magnetic poles.
4. CHALLENGE When students use magnets and compasses, they often touch
the magnets to the compasses. Then they find that the compasses point
south. Explain why this might occur.
Figure 5
Figure 4
When an object containing certain ferromagnetic materials is heated in the presence of a strong
magnet, thermal energy frees the atoms in each of the object’s domains. The domains can rotate
and align with the magnet’s poles. The object is then cooled while it is still in the presence of the
strong magnet. After cooling, the object’s atoms are less free to rotate. Therefore, when the strong
magnet is removed from the object, the object remains magnetized. A permanent magnet has
been created. If this permanent magnet is later reheated or dropped, however, the atoms can
jostle out of alignment, reordering the domains and removing the magnetic properties.
History of Earth’s magnetism
Magnetic domains in rocks containing iron record the
history of Earth’s magnetism. Rocks on the seafloor form when molten rock (magma) pours out
of cracks in the bottom of the oceans. As the magma cools into rock, the domains in the ironcontaining rocks align in the direction of Earth’s magnetic field. These rocks become weak
permanent magnets. As more magma pours out of the cracks, the older rocks are pushed away
from the cracks. As a result, rocks farther from the cracks are older than those near the cracks.
Scientists who first examined seafloor rocks were surprised to find that the alignment of
domains varied in the iron of rocks of different ages. They concluded that Earth’s magnetic north
and south poles have exchanged places many times during Earth’s history.
Magnetic Fields Around Magnets
When you investigate simple magnets, you notice that the forces between magnets are present
not only when magnets touch each other, but also when magnets are held apart. Just as the
existence of long-range electric and gravitational forces can be interpreted as being the result of
electric and gravitational fields, long-range magnetic forces can be interpreted as being the result
of magnetic fields. These fields transfer energy through space.
Magnetic fields are fields that exist in space where magnets would experience a force. They are
vector quantities because they have magnitude and direction. The needle of a compass in Earth’s
magnetic field aligns in the direction of Earth’s field. When in a stronger magnetic field, the
needle realigns in the direction of the stronger field.
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Doug Martin
1. a. repulsive
b. attractive
2. south, north, south, north
3. Earth is like a giant magnet. Earth’s geographic North
Pole is actually its magnetic south pole. The north end of
a compass needle, therefore, points to Earth’s magnetic
south pole.
4. When students bring compasses near magnets, the
­magnetization of the compass flips.
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INTERACTIVE CONTENT
Explore and Explain:
Magnetic Fields Around
Magnets
Vasily Kovalev/shutterstock
Est. time: 2 min
550
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Quick Practice
Two Dimensions
Obtaining, Evaluating, and Communicating Information
Before beginning renovations or when hanging heavy
paintings, it is important to locate the studs in a wall w
­ ithout
damaging the wall. The capacitive stud finder is able to
­distinguish between the densities of building materials
such as wallboard and wooden framing components
(i.e., studs). The two materials have different dielectric
­constants, so a stud that lies behind a wall can be detected
as a difference in capacitance. The old-fashioned ­magnetic
stud finder uses a small magnet that can rotate. The
magnet turns upright when it is over a nail in a stud. Have
students do further research on how a stud finder works
and draw a visual informative diagram to share with their
class on their findings.
Three Dimensions
Figure 6 Iron filings on paper illustrate the magnetic field of a bar magnet two-dimensionally (left) and iron
filings on an upright magnet illustrate the magnetic field three-dimensionally (right).
Visualizing magnetic fields What do magnetic fields look like? Like electric and
gravitational fields, magnetic fields are invisible. But we can visualize them in a few different
ways. One way is to place iron filings around a magnet. Each long, thin iron filing around a
magnet becomes a temporary magnet by induction. Just like thousands of tiny compass needles,
each iron filing rotates until it is parallel to the magnetic field. You can see the results both
two-dimensionally and three-dimensionally in Figure 6.
(l)Alchemy/Alamy; (r)Yon Marsh/Alamy Stock Photo
Magnetic field lines Scientists visualize
magnetic fields using magnetic field lines, such as
those shown in Figure 7. Like electric field lines,
magnetic field lines are not real. They are used to
show the direction as well as the strength of a
magnetic field. The number of magnetic field lines
passing through a surface perpendicular to the
lines is the magnetic flux. The flux per unit area is
proportional to the strength of the magnetic field.
Magnetic flux is most concentrated at magnetic
poles, where magnetic field strength is the
highest.
The direction of a magnetic field line is defined as
the direction in which the north pole of a compass
points when placed in a magnetic field. Therefore,
field lines emerge from a magnet’s north pole and
enter at its south pole, as in Figure 7. The field
lines form closed loops, continuing through a
magnet from its south pole to its north pole.
B
N
Enrichment
S
B
Figure 7 Magnetic field lines can be visualized as lines leaving
the north pole of a magnet, entering the south pole, and passing
through the magnet, forming closed loops. Magnetic fields are
traditionally represented by the letter B.
COLOR CONVENTION
Magnetic field line (B)
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Metal Surgical Implants Are Not Magnetic A metal plate
is sometimes used to fill a defect in the skull, which may
arise from trauma, surgery, or another cause. Thanks to
­Hollywood and some fiction writers, students might think
that it is possible to use a magnetic field to attract these
metal plates. However, like many other metal surgical
implants, these plates are made of titanium, which is
­nonmagnetic.
04:34PM
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Differentiated Instruction
EL OL Visually Impaired Have students handle two
common ceramic magnets. Ask them to move the magnets together, face-to-face, and notice if there is a force of
attraction or repulsion. If there is repulsion, have them describe any changes they observe as they try to bring the
magnets closer together. Next, have them turn one of the
magnets so the opposite face is presented and repeat the
experiment. Students should observe a force in the direction opposite to what they first experienced. Ask them
if the face of a ceramic magnet is a pole. If it ­attracts or
repels other magnets, then it is a magnetic pole.
Lesson 1 • Understanding Magnetism
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Lesson 1: Understanding Magnetism
Visual Literacy
Discussion
Discourse: Oersted observed the rotation of a compass
needle in response to current in a nearby wire. Ask
students how Oersted’s observations might have changed
if he had used a variable resistor in series with the wire
and the power supply. He probably would have noticed
a relationship between the circuit resistance and the
deflection of the needle. He might have concluded that
there was an indirect relationship between resistance and
deflection and a direct relationship between current and
deflection.
Forces on objects in magnetic fields
You read earlier that a magnet
can polarize ferromagnetic materials. How can this be explained in terms of
magnetic fields and forces?
Forces on permanent magnets Magnetic fields exert forces on magnets.
When like poles of two magnets are close together, the field produced by the
north pole of one magnet pushes the north pole of the second magnet away in
the direction of the field lines, as shown by the iron filings in the top panel of
Figure 8. Now look at the bottom panel of Figure 8. The field from the north
pole of one magnet now acts on the south pole of the second magnet, attracting
it in a direction opposite the field lines. The magnetic field is continuous, forming arcs from one magnet to the other.
other magnets. They also exert forces on ferromagnetic materials. When an
object containing a ferromagnetic material is placed in the field of a permanent
magnet, field lines leave the magnet’s north end and enter the end of the object
that is closest to the magnet. The field lines pass through the object and loop
back to the magnet’s south pole. The domains in the object align their poles
along the field lines, making the end of the object closest to the magnet’s north
pole the object’s south pole. The object’s new south pole is then attracted to the
magnet’s north pole, and the object’s new north pole is repelled.
Electromagnetism
Unlike poles attract.
In 1820, while doing a lecture demonstration, Danish physicist Hans Christian
Oersted laid a wire across the top of a compass and connected the ends to a
battery to complete an electric circuit. The compass was oriented so its needle
was parallel to the wire, as shown in the left side of Figure 9.
Current Off
Power
supply
OFF
+
Compass
Figure 8 Iron filings can be used to
visualize the magnetic field around two
like poles (top) and around two unlike
poles (bottom). The iron filings help us
understand how like poles repel and
unlike poles attract.
Current On
current
AC
DC
Power
supply
ON
-
current
AC
DC
OFF
ON
+
-
Compass
Figure 9 The needle of a compass
under a wire and originally parallel
to the wire when current is off (left)
moves so it is perpendicular to the
wire when current is on (right).
Quick Practice
Developing and Using Models Electromagnetic cranes
can lift and release on ­command. Waste management
workers use such cranes to move wrecked cars and
trucks in junkyards, among o
­ ther things. Challenge
students to build a ­working model of an electromagnetic
crane that will lift and ­release a toy car.
Like poles repel.
Forces on temporary magnets Magnetic fields exert forces not only on
552
Richard Hutchings/Digital Light Source
Have students study Figure 8. Ask students how the
concept of repulsion could be a
­ pplied in a transportation
system to improve energy efficiency. With maglev trains,
strong magnets (electromagnets) are used to produce
magnetic repulsion between the train and the track. By
eliminating physical contact between the train and the
track, friction is eliminated. With friction eliminated, less
energy is required to propel the train.
Module 20 • Magnetism
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INTERACTIVE CONTENT
Explore and Explain:
Electromagnetism
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Critical Thinking
When Oersted turned the current on, he was amazed to see that the needle moved so
it was perpendicular to the wire, as it is in the right side of Figure 9. When Oersted
placed the compass on top of the wire, the needle again became perpendicular to the
wire, but it pointed in the other direction. The same thing happened when he
reversed the current’s direction: the compass needle reversed direction. When he
turned off the current, the needle returned to its original position.
Oersted’s conclusion—that a current produces a magnetic field—was the first hint
that a connection exists between magnetism and electric currents. As you will read,
the relationship between magnetism and electric current underlies the design and
operation of many modern devices.
Magnetic Field Around a Wire
Right-HandRule
Rule
Right-Hand
Right
hand
Get It?
Summarize Oersted’s conclusion in your own words.
Magnetic fields from current-carrying wires The magnetic field
around a current-carrying wire is always perpendicular to that wire. Just as field
lines around permanent magnets form closed loops, the field lines around currentcarrying wires also form closed loops. The circular pattern of iron filings shown in
the top panel of Figure 10 represents these loops. The strength of the magnetic field
around a long, straight wire is proportional to the current in that wire. Magnetic
field strength also varies inversely with distance from the wire.
Direction of the magnetic field How can you find the direction of the magnetic
field around a current-carrying wire? Scientists use right-hand rules to describe how
the directions of electric and magnetic properties relate. In this case, imagine holding a length of wire with your right hand, as shown in Figure 10. If your thumb
points in the direction of the conventional (positive) current, as it does in the bottom
panel of Figure 10, the fingers of your hand encircling the wire will point in the
direction of the magnetic field.
Current
Direction of
magnetic
field
Figure 10 The circular patterns
formed by iron filings around a
current-carrying wire (top) represent
the magnetic field around the wire.
You can determine the direction of the
magnetic field around the wire using a
right-hand rule (bottom).
Analyze What happens to the
magnetic field around a wire when
current changes direction?
Cause and Effect Have students review Oersted’s
­investigations and generate questions before developing
their answer, such as
sciencephotos/Alamy Stock Photo
encircling that wire. What do you think happens to the magnetic field around a wire
formed into a loop? An electric current in a single loop of wire forms a magnetic field
all around the loop, as shown in the left panel of Figure 11 on the next page. By
applying a right-hand rule to any part of the loop in Figure 11, you can see that the
direction of the magnetic field inside the loop is always the same.
What did Oersted investigate?
What empirical evidence did Oersted observe?
CROSSCUTTING CONCEPTS
Cause and Effect Study Figure 9 on the previous page. What empirical evidence
did Oersted observe that led him to the conclusion that electric current produces a
magnetic field?
Lesson 1 • Understanding Magnetism
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Chapter: 20
Get It?
Electric current produces an electric field.
Crosscutting Concepts
Electromagnets You just read that a current in a wire produces a magnetic field
Program: HSS_NA Component: Lesson
Constantly Changing Fields Ask students to predict what
would happen to an iron bar placed into a magnetic field
with constantly changing polarity. Then ask them to elaborate, assuming the domains resisted reorientation. The
domains will constantly realign with the alternating field.
Since the domains resist this change, heat results just as
friction results in heat in mechanical systems. The heat
from domain realignment is called hysteresis loss. Designers of motors and transformers use silicon steel alloys to
minimize this loss. Since the domains in silicon steel are
easily reoriented, it is not useful as a permanent magnet.
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Caption Question Fig. 10: The field would go in the
­opposite direction, but it would remain at a right angle
to the current.
05:24PM
Physics Challenge Activity
Magnetized Steel Ask students how they would identify
which of several steel bars were magnetized and which
were demagnetized, using only the steel bars. Only the
magnetized steel bars would show a force of repulsion.
The process could begin by randomly selecting two bars,
bringing the bars together end-to-end, and then flipping
one bar end-for-end. Eventually, a force of repulsion will
be discovered. This would identify the selected bars as
permanent magnets. Then, each remaining bar could be
tested at each end against one end of a magnetized bar.
The demagnetized bars would show attraction at both
ends. Also, if two demagnetized bars are selected, no
force would be detected as the ends are brought together.
Caption Question Fig. 11: Inside the solenoid, the
­contributions to the magnetic field from all sides of the
solenoid add up, creating a stronger overall magnetic
field. Outside the solenoid, the contributions to the overall
­magnetic field from the near and far sides of the solenoid
are in opposite directions, making a much weaker overall
magnetic field.
Lesson 1 • Understanding Magnetism
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Lesson 1: Understanding Magnetism
PRACTICE Problems
5.
6.
7.
8.
a. twice as strong b. three times as strong
a. from south to north
b. west
the pointed end
Use the iron rod. Iron would be attracted to a permanent
magnet and take on properties of a magnet, whereas
­aluminum or glass would not. This effect would support
the magnetic field in the wire coil and thus make the
strongest electromagnet.
9. Yes. Connect the potentiometer in series with the p
­ ower
supply and the coil. Adjusting the potentiometer for
more resistance will decrease the current and the field
strength.
Elaborate
Return to the DQB and have students determine what
questions they can answer. At this point, they should be
able to answer the Focus Question.
Magnetic Field Around a Loop
Inside the loop, the field is toward you.
Outside the loop, it is away from you.
Magnetic
field
I
I
I
I
Figure 11 You can model the
direction of the magnetic field
around a loop of current-carrying
wire and around a solenoid.
Assess Is the magnetic field greater
inside or outside the solenoid?
Now think about a wire with many loops. A wire connected to a circuit and coiled into many
spiral loops is a solenoid. When current is turned on in a solenoid, each loop produces its own
magnetic field. The fields are all in the same direction, as shown in the right panel of Figure 11,
so the fields add together. When there is an electric current in a solenoid, the solenoid has a
magnetic field similar to the field of a permanent magnet. This kind of magnet is an
electromagnet. An electromagnet is a magnet whose magnetic field is produced by electric
current.
Loops and field strength Solenoids can be exceptionally strong electromagnets, producing
magnetic fields much stronger than those around permanent magnets. The strength of the
magnetic field in a solenoid is proportional to the current in the solenoid’s loops. It is also
proportional to the number and spacing of loops. The more loops there are in a solenoid and the
closer they are spaced, the greater the solenoid’s magnetic field strength. The magnetic field
strength of a solenoid also can be increased by placing an iron-containing rod inside it. An iron
rod strengthens the solenoid’s magnetism because the solenoid’s field produces a temporary
magnetic field in the iron, just as a permanent magnet produces a temporary magnet in a
ferromagnetic object.
Right-hand rule for a solenoid You can use a right-hand rule to determine the direction of
the magnetic field around a solenoid when current is on. Imagine holding a solenoid with your
right hand. If you curl your fingers around the solenoid in the direction of the conventional
(positive) current, as in Figure 12, your thumb will point toward the solenoid’s north pole.
Right-Hand Rule
Evaluate
N
S
I
Formative Assessment Check
Ask students what would happen if the current in the
wires of an electromagnet were reversed. The poles
of the electromagnet would reverse, but ferromagnetic
materials would still be attracted to the electromagnet.
Magnetic Field in a Solenoid
The magnetic fields of the loops inside a
solenoid are all in the same direction.
-
554
I
+
Figure 12 Imagine you are holding
the solenoid with your right hand.
Your thumb will point toward the
solenoid’s north pole when you curl
your fingers in the direction of the
conventional current.
Module 20 • Magnetism
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Ask students what would happen if the wiring of a
­solenoid-type electromagnet were wrapped in both
directions (i.e., counter-clockwise and clockwise). The
wires in each direction would produce opposing magnetic fields, which would act against each other, resulting in
a weaker overall magnetic field.
Remediation The colored (often blue) end of a compass
needle is called the north-seeking pole or simply the
north pole. Ask students to draw a conclusion about the
identification and location of Earth’s magnetic poles.
The blue end of the needle points to Earth’s magnetic
north pole. In principle, you could walk along, following
the needle, until it pointed down into the ground. This
point would be Earth’s magnetic north pole. Then ask
students how they would use a compass to verify the
right-hand rule for a magnetic field around a solenoid.
Hold the solenoid in your hand as shown in Figure 12 and
allow current to flow through the solenoid as shown in
the figure. If you hold the compass near the end of the
solenoid that your thumbs points to, the north-seeking
pole of the compass should point toward your thumb.
554
Module 20 • Magnetism
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Three-Dimensional Thinking
PRACTICE Problems
Applying Practices
ADDITIONAL PRACTICE
5. How does the strength of a magnetic field that is
1 cm from a current-carrying wire compare with
each of the following?
a. the strength of the field 2 cm from the wire
b. the strength of the field 3 cm from the wire
6. A long, straight current-carrying wire lies in a
north-south direction.
a. The north pole of a compass needle placed
above this wire points toward the east. In what
direction is the current?
b. If a compass were placed underneath this wire,
in which direction would the compass needle
point?
7. A student makes a magnet by winding wire around
a nail and connecting it to a battery, as shown in
Figure 13. Which end of the nail—the pointed end
or the head—is the north pole?
The online Applying Practices project Modeling Magnetic
Fields can be used to assess students’ mastery of performance expectation HS-PS3-5.
8. You have a battery, a spool of wire, a glass rod, an
iron rod, and an aluminum rod. Which rod could
you use to make an electromagnet that can pick
up steel objects? Explain.
9. CHALLENGE The electromagnet in the previous
problem works well, but you would like to make
the strength of the electromagnet adjustable by
using a potentiometer as a variable resistor. Is this
possible? Explain.
-
Check Your Progress
+
Figure 13
Check Your Progress
10. Electromagnets Explain how to construct an
electromagnet.
11. Magnetic Fields What two things about a
magnetic field can magnetic field lines
represent?
12. Magnetic Forces Considering magnetic
forces, how are forces at distance explained?
13. Magnetic Fields Where on a bar magnet is
the magnetic field the strongest?
14. Magnetic Fields Two current-carrying wires
are close to and parallel to each other and
have currents with the same magnitude. If the
two currents were in the same direction, how
would the magnetic fields of the wires be
affected? How would the fields be affected if
the two currents were in opposite directions?
16. Electromagnets A glass sheet with iron
filings sprinkled on it is placed over an active
electromagnet. The iron filings produce a
pattern. If this scenario were repeated with
the direction of current reversed, what
observable differences would result? Explain.
17. Magnetic Domains Explain what happens to
the domains of a temporary magnet when the
temporary magnet is removed from a magnetic field.
18. Critical Thinking Imagine a toy containing
two parallel, horizontal metal rods, one above
the other. The top rod is free to move up and
down.
15. Direction of the Field Describe how to use a
right-hand rule to determine the direction of
a magnetic field around a straight, currentcarrying wire.
a. The top rod floats above the lower rod. When
the top rod’s direction is reversed, however, it
falls down onto the lower rod. Explain how
the rods could behave in this way.
b. Assume the toy’s top rod was lost and another
rod replaced it. The new rod falls on top of the
bottom rod no matter its orientation. What type
of material is in the replacement rod?
Go online to follow your personalized learning path to review, practice,
and reinforce your understanding.
Lesson 1 • Understanding Magnetism
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Chapter: 20
ADDITIONAL RESOURCE
Applying Practices:
Modeling Magnetic Fields
05:24PM
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ADDITIONAL RESOURCE
Vocabulary Flashcards:
Understanding Magnetism
PROJECT
ADDITIONAL RESOURCE
Lesson Check:
Understanding Magnetism
ADDITIONAL RESOURCE
Inspire Physics LearnSmart
10. Y
ou could connect either end of a wire to a source of
current. The strongest electromagnets are solenoids,
where wire in a circuit is wrapped around a ferromagnetic rod, such as iron, which increases field strength.
11. F
ield lines represent the strength and the direction of a
magnetic field.
12. S
tudent answers may vary. Answers could include
magnets on a refrigerator and Earth’s magnetic field.
The effects of these forces can be demonstrated by
bringing another magnet, or a ferromagnetic material,
nearby.
13. at the poles
14. If the currents were in the same direction, the ­magnetic
field would be approximately twice as large; if the
currents were in opposite directions, the field would be
approximately zero.
15. If you grasp the wire with your right hand with your
thumb pointing in the direction of the conventional
­current, your fingers curl in the direction of the field.
16. N
one; the filings would show the same field pattern.
However, a compass would show that the magnetic
polarity had reversed.
17. T
he domains return to a random arrangement because
they no longer align with the domains of the field of the
permanent magnet.
18. a. T
he metal rods could be magnets with their axes
parallel. If the top magnet is positioned so that its
north and south poles are above the north and
south poles of the bottom magnet, it will be repelled and float above. If the top magnet is turned
­end-for-end, it will be attracted to the bottom magnet.
b. ferromagnetic
Formative Assessment: Lesson Check
GO ONLINE You might want to assign from the
Additional Resources the pre-made Lesson Check based
on key concepts and disciplinary core ideas, or you can
customize your own using the customization tool.
Lesson 1 • Understanding Magnetism
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Lesson 2: Applying Magnetic Forces
Types of Interactions
PS2.B Forces at a distance are explained by fields
(gravitational, electric, and magnetic) permeating
space that can transfer energy through space.
Magnets or electric currents cause magnetic fields;
electric charges or changing magnetic fields cause
electric fields.
*Bold font indicates the part of the DCI covered in
this lesson.
LESSON 2
APPLYING MAGNETIC FORCES
FOCUS QUESTION
What role do magnetic forces play in everyday life?
Forces on Current-Carrying Wires
When you put a magnet in a magnetic field, the magnet can move. What happens when you put
a current-carrying wire in a magnetic field? Michael Faraday, who performed many electricity and
magnetism experiments during the nineteenth century, discovered that a magnetic field produces
a force on a current-carrying wire. The force on the wire is always at right angles to both the
direction of the magnetic field and the direction of current, as shown in the left part of Figure 14.
When current changes direction, so does the force.
Direction of force
Launch the Lesson Interactive Content can be assigned
the night before class as a lesson preview, during class
to spark discussion, as a resource during inquiry, or as
homework.
CCC
I
I
3D THINKING
Disciplinary Core Ideas
COLLECT EVIDENCE
Use your Science Journal to
record the evidence you collect as
you complete the readings and
activities in this lesson.
556
B
Figure 14 You can use a right-hand rule
to determine the direction of force when
the current (I) and the magnetic field (B)
are known.
Predict what would happen to the force if
the current changed direction.
Crosscutting Concepts
Science & Engineering Practices
INVESTIGATE
GO ONLINE to find these activities and more resources.
Virtual Investigation: Charge in a Magnetic Field
Carry out an investigation to determine the effect a magnetic field has on a moving,
electrically charged particle.
Revisit the Encounter the Phenomenon Question
What information from this lesson can help you answer the Unit and Module questions?
Module 20 • Magnetism
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PRESENTATION
Teacher Presentation:
Applying Magnetic Force
Chapter: 20
05:24PM
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INTERACTIVE CONTENT
Launch the Lesson:
Applying Magnetic Force
DC
SEP
Science Journal Remind students to keep records of
their investigations in their Science Journals. Additionally,
be sure that each reading or activity is added to the
class Summary table.
Three-Dimensional Thinking The activities called out
in the Student Edition will allow students to practice threedimensional thinking. Worksheets for these activities can
be found online.
F
B
I
Explore and Explain
Right-Hand Rule
F
DC
Driving Question Board
Have students revisit the DQB to remind themselves of the
Unit and Module questions. Have them identify the sticky
note questions they think will be answered in this lesson.
Then, have students read the Focus Question and add it
to the DQB. Students will revisit the Focus Question at the
end of the lesson.
Arrows in three dimensions The relationship among magnetic field, electric current, and
force is three-dimensional. How do you accurately represent directional arrows in three dimensions on a two-dimensional piece of paper?
SEP
Engage
You can use a right-hand rule to determine the direction of force on a
current-carrying wire in a magnetic field. Point the fingers of your right hand in the direction of
the magnetic field. Point your thumb in the direction of the wire’s conventional (positive) current.
The palm of your hand will face in the direction of the force acting on the wire, as shown in the
right part of Figure 14.
I
CCC
Reinforcement
Changing Directions Using Figure 14, have students
­consider what happens to the force when the current is in
the opposite direction, when the magnetic field is in the
opposite direction, or when both are in opposite directions.
For the first two cases, the direction of force reverses. For
the last case, the direction of force doesn’t change.
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Module 20 • Magnetism
IMPLEMENTATION OPTIONS
Presentation: Teacher-Facilitated Pathway
Use the Teacher Presentation to support classroom
instruction and spark discourse. Obtain data to
inform your instruction by assigning the Interactive
Content, Additional Resources, and Assessment.
Interactive Content: Student-Led Pathway
Students can use the online Interactive Content,
along with the Student Edition, Science Notebook,
projects, and labs, to collect evidence to support
their claim. They can record their evidence in their
Science Journals and the class Summary Table.
Hero Images Inc./Alamy
Caption Question Fig. 14: The force would reverse
­direction, so it would push down instead of up.
THIS INFORMATION IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.
Use an Analogy
Field out of Page
Field into Page
F
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
I
X
FX
X
Field out of Page
X
X
X
X
Figure 15 Dots represent a magnetic field coming out of the
page, toward you (left). Crosses represent a magnetic field
going into the page, away from you (right). Note that the force
on each wire is perpendicular to both the magnetic field and
the current.
X
I
Field out of Page ARROW CONVENTION
Field into Page
Field into Page B out of
X the page
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
FX
X
X
X
X
X
X
X
Imagine an archer shooting an arrow toward you. The arrow looks like
a dot.
theX
F X NowXimagine
X
X
F
same arrow going away from you. The arrow looks
like a cross. You can use dots to represent
I
magnetic fields that go into a piece of paper, and crosses to represent Xfields Xthat FgoX out ofX the X
I
I
paper, as shown in Figure 15.
Magnitude of force
X
B into
X the page
X
I
X
X
X
You read that you use a right-hand rule to find the direction of the
force from a magnetic field on a current-carrying wire. How do you find the magnitude of this
force? Experiments show that the magnitude of the force (F) on a current-carrying wire is
proportional to the wire’s current (I), the wire’s length (L), the strength of the magnetic field (B),
and the sine of the angle between the current and the magnetic field (sin θ). Recall that you
measure force in newtons (N) and current in amperes (A). You measure the strength of a
magnetic field (B) in teslas (T). One T equals 1 N/(A⋅m).
The magnitude of the force on a current-carrying wire in a magnetic field is equal to the
product of the current, the length of the wire, the field strength, and the sine of the angle
between the current and the magnetic field.
Procedure Lay the magnet on a table and position the
middle portion of the wire approximately 1 cm from one
of the poles of the magnet. Connect the ends of the wire
to the battery terminals. The wire should move. If not, the
magnetic field may be parallel to the wire, so change the
orientation of the magnet with respect to the wire. Now,
without changing the orientation of the wire in the vicinity of the magnet, reverse the wire ends on the battery
terminals to show that the force between the magnet and
wire reverses.
F = ILB (sin θ)
Note that sin 0° = 0, and sin 90° = 1. This means that when the current and the magnetic field
are parallel to each other, the force on a current-carrying wire is zero. The force on the wire is
greatest when the current and the magnetic field are perpendicular to each other.
Richard Hutchings/Digital Light Source
Earbuds
You might wonder how people apply the
relationship among magnetic fields, electric currents, and
force in today’s technology. You are probably familiar with
one example—earbuds. If you look inside an earbud, such as
the one in Figure 16, you will find a tiny coil of wire
attached to a thin plastic membrane. Beneath the
membrane is a permanent magnet. The magnetic field from
the permanent magnet is oriented radially so it is
perpendicular to both the coil of wire and the direction of
motion of the coil.
Lesson 2 • Applying Magnetic Forces
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INTERACTIVE CONTENT
Explore and Explain: Forces
on Current-Carrying Wires
Quick Demo
Brute Force on Wire
Materials permanent magnet, lightweight wire,
6-V ­battery
Force on a Current-Carrying Wire in a Magnetic Field
Figure 16 An earbud works because an
electric current in a wire is affected by a
magnetic field.
Magnetic Fields Review how a static charge produces an
electrostatic field that, in turn, produces a force on a nearby second static charge. Discuss how permanent magnets and current-carrying wires produce magnetic fields.
A moving charge produces a magnetic field that produces
a force on another moving charge. Help students draw an
­analogy between the static charges and the electrostatic
field ­versus moving charges and the magnetic field.
Est. time: 10 min
04:15PM
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INTERACTIVE CONTENT
Explore and Explain: Wired
Devices
Critical Thinking
Thought Experiment Ask students what would happen if
you took a sturdy loudspeaker and plugged it directly into
the wall socket. WARNING: Do this only as a thought
experiment! If the speaker is not sturdy enough, it may
explode. If the speaker’s coil is of sufficiently low resistance
to allow an excessive current, the current may be high
enough to overheat and damage the speaker or trip the
circuit breaker.
(l, c)McGraw-Hill Education; (r)Richard Hutchings/Digital Light Source
Reinforcement
Right-Hand v. Left-Hand Rules The right-hand rules are
appropriate for analyzing magnetism from conventional
currents (i.e., current is in the direction in which positive
charge flows). Those who think about electron current
often use the left-hand rules.
Demonstrate the left-hand rule for students by showing
them a “hitchhiker’s” fist (left handed, of course). You know
that the magnetic field produced by an electric current
is always oriented perpendicular to the direction of the
current. The left-hand rules says that, if the thumb points
in the direction of the electron current, the curled fingers
point in the direction of the magnetic flux lines produced
by the electron current.
Lesson 2 • Applying Magnetic Forces
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Lesson 2: Applying Magnetic Forces
Clarify a Preconception
Students might be concerned about forces that they
­believe would be exerted on either end of the loop in
Figure 17. Assuming the ends of the loop are inside the
magnetic field, the currents at the ends are either in the
same direction as the magnetic field or in the opposite
direction. In both cases, there is no force because a magnetic field does not produce a force on a current that is
parallel to the magnetic field. It only ­produces a force when
the current is nonparallel to the magnetic field lines.
Physics Project Activity
Uses of Superconducting Magnets Have each student research a particular application of superconducting magnets
and write a brief (two-page) report on that application. Accept both current and future applications as topics. Some
possibilities include magnetic levitation, fusion reactors,
nuclear magnetic resonance spectroscopy, MRI, particle
accelerators, and high-­efficiency propulsion systems.
STEM Connections
GO ONLINE to see STEM Connections, a diverse
selection of people and groups that have made important
contributions to society through science and technology.
Wire Loop
B
Galvanometer
F
Iout
Coil
Spring
Iin
Soft iron
core
Magnetic
torque
I
Figure 17 When a wire loop is placed in a magnetic field and current is turned on, the loop rotates
(left). The coil in a galvanometer (right) rotates in proportion to the magnitude of the current.
Explain what causes the wire loop to rotate.
A music player sends current through an earbud’s wires. The current enters the coil, changing
direction between 40 and 40,000 times each second, depending on the pitches of the tones it
represents. The force from the magnetic field on the coil pushes the coil in and out, depending
on the direction of current. This causes the membrane to vibrate, thereby producing sound
waves. Each time the current changes direction twice, the membrane vibrates back and forth once.
Most loudspeakers and headphones work in a similar way. A magnetic field exerts a force on a
coil of wire mounted on a paper or plastic cone. As the wire moves, it pushes the coil into and
out of the field. This motion causes the cone to vibrate and produce sound waves.
Galvanometers
You can use the force that a magnetic field exerts on a loop of currentcarrying wire to measure currents. How does this work? Current in the wire loop shown in the
left of Figure 17 passes in one end of the loop and out the other. As it does, the force on the loop
pushes one side of the loop down and the other side up. The resulting torque causes the loop to
rotate. The magnitude of the torque on the loop is proportional to the magnitude of the current.
This is the principle used in a galvanometer.
A galvanometer is a device used to measure very small currents. The torque of a small coil
spring in this device opposes the torque from the current in the wire loop. The amount of
rotation is proportional to the current. The meter is calibrated by determining how much the coil
turns when a known current is sent through it, as shown in the right of Figure 17. The
galvanometer can then be used to measure unknown currents.
STEM CAREER Connection
Magnetic Resonance Imaging (MRI) Technologist
MRI technologists use an MRI machine, which is essentially a large tube-shaped
magnet, and radio waves to create detailed cross-sectional images of the organs
and tissues in the body. These images are tools used to diagnose and treat
diseases and other medical conditions. If you like helping people, then a career as
an MRI technologist might be for you.
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EL Support
ELD PI.11/12.6a
EMERGING LEVEL Draw students’ attention to
the use of thereby in the first paragraph. Support
students in recognizing that thereby is used to show
a result. Ask: What is the result? sound waves
EXPANDING LEVEL Draw students’ attention to the use
of thereby in the first paragraph. Point out the action
described in the clause before thereby. Elicit that thereby
introduces a result. Ask: What does thereby introduce?
the result: “producing sound waves.”
BRIDGING LEVEL Ask students which word in the first
paragraph introduces a result. thereby Discuss with
students other ways to introduce a result: therefore, as a
result, resulting in, etc.
558
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PRACTICE Problems
19. Y
ou would use the right-hand rule for magnetic force
on a wire. When you point the fingers of your right
hand in the direction of the magnetic field and your
thumb in the direction of the wire’s conventional
(positive) current, the palm of your hand will face in the
direction of the force acting on the wire. To use this
method, you would need to know the direction of the
current and the direction of the field.
EXAMPLE Problem 1
CALCULATE THE STRENGTH OF A MAGNETIC FIELD A straight wire carrying a 5.0-A current is in a
uniform magnetic field oriented at right angles to the wire. When 0.10 m of the wire is in the field, the
force on the wire is 0.20 N. What is the strength of the magnetic field (B)?
1 ANALYZE AND SKETCH THE PROBLEM
• Sketch the wire and show the direction of the current with an arrow, the magnetic field as B, and the
force on the wire as F.
• Determine the direction of the force using the right-hand rule for the force on a current-carrying wire
in a magnetic field. The field, the wire, and the force are all at right angles.
Known
I = 5.0 A
Unknown
B=?
L = 0.10 m
2 SOLVE FOR THE UNKNOWN
B is uniform, and because B and I are perpendicular to each other, F = ILB.
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X BX
F = ILB
l
l l
F = 0.20 N
X
L
20. 1.6 N
21. 0.13 T
F
Solve for B.
F
B = __
IL
0.20 N
= __________
(5.0 A)(0.10 m)
Substitute F = 0.20 N, I = 5.0 A, L = 0.10 m.
= 0.40 N/A·m = 0.40 T
22. 0.15 T
C20_025A-674235
B is 0.40 T from left to right and perpendicular to I and F.
23. 7.8 A
3 EVALUATE THE ANSWER
• Are the units correct? The answer is in teslas, the correct unit for a magnetic field.
• Is the magnitude realistic? A magnetic field with a strength under 1 T is realistic.
24. O
ne pole should be held as close to the coil as possible so that the field lines are perpendicular to both the
wires and the direction of motion of the plate.
ADDITIONAL PRACTICE
PRACTICE Problems
19. Explain the method you could use to determine the direction of force on a current-carrying wire at right angles
to a magnetic field. Identify what must be known to use this method.
20. A wire that is 0.50 m long and carrying a current of 8.0 A is at right angles to a 0.40-T magnetic field. How
strong is the force that acts on the wire?
21. A wire that is 75 cm long and carrying a current of 6.0 A is at right angles to a uniform magnetic field. The
magnitude of the force acting on the wire is 0.60 N. What is the strength of the magnetic field?
22. A 40.0-cm-long copper wire carries a current of 6.0 A and weighs 0.35 N. A certain magnetic field is strong
enough to balance the force of gravity on the wire. What is the strength of the magnetic field?
23. How much current would be required to produce a force of 0.38 N on a 10.0-cm length of wire at right angles to
a 0.49-T field?
24. CHALLENGE You are making your own loudspeaker. You make a 1-cm-diameter coil with 20 loops of thin wire.
You use hot glue to fasten the coil to an aluminum pie plate. The ends of the wire are connected to a plug that
goes into the earphone jack on an MP3 music player. You have a bar magnet to produce a magnetic field. How
would you orient the magnetic field to make the plate vibrate and produce sound?
Lesson 2 • Applying Magnetic Forces
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Use with Example Problem 1.
Problem
What is the force on a 12-cm straight wire in a 1.9-T
­magnetic field when the current in the wire is 25 A?
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ADDITIONAL IN-CLASS Example
05:24PM
Response
F = ILB = (25 A)(0.12 m)(1.9T) = 5.7 N
Quick Demo
Energy Conversion
Materials 1.5-V alkaline D-cell battery, wire, loudspeaker
Procedure Demonstrate how the speaker converts
electrical energy to sound energy. Stick a piece of ferromagnetic material on the back side of the speaker first,
to show that the speaker has a magnet. With the wires
connected to the speaker contacts, brush one wire along
one of the battery contacts to produce a crackling sound.
Then have students observe the direction of cone movement when there is a steady current. Reverse the battery
polarity and have students notice that the cone moves
in the opposite direction. Discuss with the students how
the current in the magnetic field produces a force on the
speaker.
Est. time: 10 min
Lesson 2 • Applying Magnetic Forces
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Lesson 2: Applying Magnetic Forces
Discussion
Ask: Why are digital meters now more popular than
­analog meters? There are several reasons: (1) digital
­meters are easier to interpret, (2) analog meters are
delicate mechanical devices with many moving parts and
are thus more fragile, and (3) integrated circuit technology often makes all-electronic solutions to problems less
expensive.
Get It?
For an ammeter, connect the resistance in parallel to the
galvanometer. For a voltmeter, connect the resistor in series with the galvanometer.
Get It?
Sample answers: hair dryer, electric razor, hand mixer,
electric drill
Careers
Electrical Engineers Electrical engineers use the scientific
principles of magnetism and electromagnetism to design
motors, transformers, generators, data storage units, relays,
circuit breakers, and a wide variety of other devices. They
often work in conjunction with physicists and mechanical ­engineers. They sometimes use computers to model
­magnetic circuits and devices.
Ammeter A galvanometer can produce full-scale deflections with currents as small as
50 μA (50×10 -6 A). The resistance of the wire loop in a sensitive galvanometer is about
1000 Ω. To measure larger currents, a galvanometer can be converted to an ammeter.
To do this, you would place a resistor with small resistance in parallel with the meter, as
shown in the top of Figure 18. Because current is inversely proportional to resistance,
most of the current (Is ) passes through this resistor, called the shunt because it shunts,
or bypasses, much of the current around the galvanometer. Only a few microamps (Im )
pass through. The shunt’s resistance is chosen to produce the desired meter sensitivity.
Ammeter
+
Is
Im
Voltmeter You can also connect a galvanometer as a voltmeter. To make a voltmeter,
you would place a resistor, called the multiplier, in series with the meter, as in the
bottom of Figure 18. The galvanometer measures the current through the multiplier.
V
The current is I = __
R , where V is the potential difference across the voltmeter, and R is
the effective resistance of the galvanometer and the multiplier. Suppose you want the
voltmeter’s needle to move across the entire scale when 10 V is placed across it. You
would use a resistor so that at 10 V the meter is deflected full-scale by a 50 μA current
through the meter and the resistor.
Get It?
Compare How would you use a resistor to convert a galvanometer first to an
ammeter and then to a voltmeter?
Rshunt
G
Voltmeter
+
Rmultiplier
I
G
Figure 18 A galvanometer can be
connected for use as an ammeter
(top) and as a voltmeter (bottom).
Electric motors The simple loop of wire in a galvanometer cannot rotate more than 180°.
The force from the magnetic field pushes one side of the loop up and the other side down until
the loop reaches the vertical position. The loop will not continue to turn because the forces are
still up and down, parallel to the loop. If you could make the loop rotate continuously, you would
have an electric motor.
An electric motor is an apparatus that converts electrical energy into mechanical energy. Electric
motors rely on a multilooped wire coil called an armature, which is mounted on an axle that
rotates in a magnetic field. Current enters the armature through a split-ring commutator, which
reverses the direction of current as the armature turns, as shown in the simple electric motor in
Figure 19 on the next page.
Although only one loop is shown in Figure 19, the armature in most electric motors has many
loops. The total force acting on the armature is proportional to nILB, where n is the total number
of turns on the armature (each completing 360°), I is the current, L is the length of wire in each
turn that moves perpendicular to the magnetic field, and B is the strength of the magnetic field.
The magnetic field is produced either by a permanent magnet or by an electromagnet (called a
field coil). The torque on the armature is controlled by varying the current through the motor.
The larger the torque, the faster the armature turns.
Get It?
Describe an object that you use at home that uses an electric motor.
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Module 20 • Magnetism
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Differentiated Instruction
AL EL Struggling Students Form small groups. Have
each group identify several applications of magnetism.
Have each group give its list to a different group. The
groups should select an item from the list that they were
given and identify the units and the equations that would
be relevant for that item. Have each group share the item,
units, and equations with the class.
560
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Enrichment
Magnetic Circuit Breakers Magnetic circuit breakers
trip when the current in a coil is high enough to move an
iron armature, which then opens the contact points. One
problem with high-energy circuit breakers is that an arc
can form when the contacts open. A magnetic field can
be used to “blow out” the arc. This is sometimes called a
magnetic quench.
Electric Motor
Armature
3
F
2
Brush
Quick Practice
Iin
1
1
Developing and Using Models Magnetic models of our
planet are often used for investigative research, navigation,
and surveys. One such model is known as the international
geomagnetic reference field (IGRF). IGRF users must be
aware of its limitations. Earth’s magnetic field is extremely
complicated in both space and time. The IGRF model does
not account for local magnetizations. Many geological formations and rocks are partially magnetized. Have students
research what type of model the IGRF is and what it is used
for. Have students write a brief report of their findings.
Split-ring
commutator
Iout
Electric Connection
Current from a battery passes through graphite brushes fixed in position but pressed against a split-ring
commutator. The commutator is attached to a wire
loop—the armature—along an axle in a magnetic field.
2 Current Reversal
Current goes through the brush to the split-ring
commutator, which passes it on to the armature. The
magnet either repels or attracts the armature, depending on the direction of current. When the armature
reaches the vertical position, each half of the commutator changes brushes. This reverses current direction so
that the armature can rotate an additional 180°.
mike davies/Alamy Stock Photo
3 Continuous Rotation
Reinforcement
Current reverses with each half-turn of the armature;
this results in continuous rotation.
Figure 19 In an electric motor, such as the one powering this drone, an armature in a magnetic field rotates 360°. A split-ring commutator changes the direction of the current every 180°, allowing this rotation.
Lesson 2 • Applying Magnetic Forces
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09:02PM
Magnetic Flicker Light Obtain a magnetic flicker light,
and ask how it works. A magnetic flicker light has a
moveable filament and a permanent magnet. When
there is current through the filament, a field is produced
that interacts with the field of the permanent magnet,
resulting in a force on the filament.
Teacher Toolbox
Content Background
Magnetic Bearings Magnetic bearings eliminate ­friction
and wear and allow high speeds of rotation. They work
by suspending a rotating steel shaft in a magnetic field.
The shaft is attracted by the field but is not allowed to
touch the poles of the attracting electromagnet. This is
accomplished by sensing shaft position and using that
information to control the amount of current in the electromagnet. As the shaft moves closer to the electromagnet, the current is decreased to weaken the field. As the
shaft moves away from the electromagnet, the current is
increased to strengthen the field. This is an example of
a ­negative feedback system where the error between a
desired parameter value and the actual parameter value
adjusts a control parameter to decrease the error.
Lesson 2 • Applying Magnetic Forces
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Lesson 2: Applying Magnetic Forces
Activity
Electrons and Magnetic Fields Older computer monitors
used cathode-ray tubes (CRT) that sent charged particles
to the screen. Liquid-crystal display (LCD) monitors work
with changing crystal structures, not moving charges. Use
a small ceramic magnet in conjunction with a CRT monitor
to demonstrate the interaction between the electrons and
the magnetic field. Repeat the demonstration with an LCD
monitor to show that there is no interaction. Follow up by
asking students why CRT displays often have demagnetizing coils wound around their envelopes. It shields the
display from changing magnetic fields. Other nearby appliances could be generating these fields.
Real-World Physics
Northern Lights The aurora borealis, also known as the
northern lights, are produced when charged particles hit
air particles in Earth’s atmosphere. The charged particles
come from the Sun. Earth’s magnetic field funnels these
charged particles toward Earth’s magnetic poles. At the
poles, these charged particles collide with air particles, exciting the atoms of those air particles. The air particles emit
light when their atoms return to a nonexcited state. This
light is visible and is called the northern lights.
Forces on Single Charged Particles
You use F = ILB(sin θ) to determine the force on a current-carrying wire in a magnetic field. A
current is simply a stream of charged particles. How do you determine the force on a single
charged particle?
Equation of force The magnetic force on a single charged particle depends on the velocity
of the particle, the strength of the magnetic field, and the angle between the directions of the
velocity and the field. Consider a single electron moving in a wire of length L that is
perpendicular to a magnetic field (B). Current (I) is equal to the charge per unit time entering the
q
wire, I = _t . In this case, q is the charge of the electron and t is the time it takes for the electron to
move the distance L.
To find the time required for a particle with speed v to travel distance L, you would use the
L
equation of motion, x = vt, or, in this case, t = __v .
q
qv
As a result, you can replace the equation for the current, I = _t , by I = __
L.
Force of a Magnetic Field on a Moving Charged Particle
The amount of force from a magnetic field on a particle equals the product of the particle’s
charge, its speed, the magnetic field strength, and the sine of the angle between the
particle’s velocity and the magnetic field.
F = qvB (sin θ)
Recall that charge is measured in coulombs (C), velocity in meters per second (m/s), and magnetic field strength in teslas (T). For a particle moving at right angles to a magnetic field,
sin θ = 1, so F = qvB.
The direction of the force on a charged particle is perpendicular to that particle’s velocity and to
the magnetic field. To find the direction of force, you can use the same right-hand rule you use for
finding the direction of the force on a current-carrying wire, where the moving charge is the
current. If the moving particle is an electron (with a negative charge), the direction of force is
reversed.
Get It?
Describe a real-life situation in which you might want to calculate the force of a
magnetic field on a moving charged particle.
CROSSCUTTING CONCEPTS
Cause and Effect Using the equation for the force of a magnetic field on a moving
charged particle, demonstrate what the force on a charged particle moving parallel
to a magnetic field would be.
Get It?
Sample answers: if you want to calculate the force of
a magnetic field on a proton in a particle accelerator; if
you want to calculate the magnetic field of Earth on a
cosmic ray
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Extension
Centripetal Acceleration When the initial velocity of a
charged particle is perpendicular to a uniform magnetic
field and no other forces are involved, the charged particle will move in uniform circular motion. Thus, the force of
the magnetic field on the charged particle is a centripetal
force. Ask students to determine the centripetal acceleration. The centripetal acceleration is determined by F = ma.
Thus, qvB = ma, or a = qvB/m.
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Chapter: 20
05:25PM
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INTERACTIVE CONTENT
Explore and Explain: Forces
on Single Charged Particles
Crosscutting Concepts
Cause and Effect Have students review the information
on the force of a magnetic field on a moving charged
particle, then have students generate questions before
formulating their demonstration, such as
What is the equation for calculating the force of a
­magnetic field on a charged particle?
Does the angle make a difference? Why or why not?
562
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PRACTICE Problems
25. down
EXAMPLE Problem 2
26. 3.2×10–12 N, up
FORCE ON A CHARGED PARTICLE IN A MAGNETIC FIELD A beam of electrons travels at
3.0×106 m/s through a uniform magnetic field of 4.0×10−2 T at right angles to the field. How strong is
the force acting on each electron?
1 ANALYZE AND SKETCH THE PROBLEM
Draw the beam of electrons and its direction of motion (v). Indicate the
magnetic field (B) and the force on the electron beam (F). Note that the
direction of force is opposite that given by the right-hand rule because
of the electron’s negative charge.
Known
v = 3.0×106 m/s
27. 8.6×10–16 N
F
28. 1.7×10–13 N
V
B
Unknown
F=?
29. 4.2×106 m/s
B = 4.0×10−2 T
30. 0.05 T
q = −1.602×10−19 C
2 SOLVE FOR THE UNKNOWN
F = qvB
= (−1.602×10−19 C)(3.0×106 m/s)(4.0×10−2 T)
ADDITIONAL IN-CLASS Example
Substitute q = –1.602×10−19 C,
v = 3.0×106 m/s, B = 4.0×10−2 T.
= −1.9×10−14 N
Use with Example Problem 2.
Problem An engineer is designing a deflection system for
an ­electron-beam device and needs a force of 2.8×10−14 N
on each electron in the beam, which travels at 1.7×106 m/s.
Determine the required field strength.
Response
3 EVALUATE THE ANSWER
• Are the units correct? T = N/(A·m) and A = C/s, so T = N·s/(C·m). Thus, (T·C·m)/s = N, the unit for
force.
• Does the direction make sense? Use the right-hand rule to verify the direction of the force, recalling
that the force on the electron is opposite the force given by the right-hand rule due to the electron’s
negative charge.
• Is the magnitude realistic? Forces on electrons and protons are always small fractions of a newton.
PRACTICE Problems
ADDITIONAL PRACTICE
25. In what direction is the force on an electron if that electron is moving
east through a magnetic field that points north?
X
X
X
X
26. What are the magnitude and direction of the force acting on the proton
B = 0.5 T
shown in Figure 20?
27. A stream of doubly ionized particles (missing two electrons and thus
X
X
X
X
carrying a net positive charge of two elementary charges) moves at a
Proton
v = 4.0×107 m/s
velocity of 3.0×104 m/s perpendicular to a magnetic field of 9.0×10−2 T.
How large is the force acting on each ion?
X
X
X
X
28. Triply ionized particles in a beam carry a net positive charge of three
elementary charge units. The beam enters a magnetic field of 4.0×10−2 T.
6
Figure
20
The particles have a speed of 9.0×10 m/s and move at right
angles to the field. How large is the force acting on each particle?
29. A singly ionized particle experiences a force of 4.1×10−13 N when it travels at a right angle through a 0.61-T
magnetic field. What is the particle’s velocity?
30. CHALLENGE Doubly ionized helium atoms (alpha particles) are traveling at right angles to a magnetic field at a
speed of 4.0×104 m/s. The force on each particle is 6.4×10−16 N. What is the magnetic field strength?
Lesson 2 • Applying Magnetic Forces
556-564_PHYS_CA_S_CH20_L2_674235.indd
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Chapter: 20
2.8×10−14 N
=​​​  ____________________
​​
​​​
(1.602×10−19 C)(1.7×106 m/s) ​
= 0.10 T
Elaborate
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F
​ ​qv ​​
B = __
05:25PM
Return to the DQB and have students determine what
questions they can answer. At this point, they should be
able to answer the Focus Question.
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Evaluate
Formative Assessment Check
Have the students consider two wires. Assume the
current in each wire flows in opposing directions. Have
students determine the direction of the magnetic field in
the vicinity of the right-hand wire that is created by the
current in the left-hand wire, and vice versa. If there is a
current up the page in the left-hand wire, it will produce
a magnetic field into the page at the right-hand wire. The
right-hand wire will have a current down the page and
produce a magnetic field into the page at the left-hand
wire. Ask students to determine the direction of the force
exerted between the two wires. If the current in the wires
is in the opposite ­direction, the force between the wires
will be repulsive.
Remediation Verify that students understand the
three right-hand rules. Draw various wire, coil, and field
examples on the board. Ask them to predict the fields,
poles, and force directions depending on the conditions
that you provide.
Lesson 2 • Applying Magnetic Forces
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Lesson 2: Applying Magnetic Forces
Check Your Progress
33. a. The magnetic field must be up, at a right angle to
the protons’ velocity. The electric fields should be
in the direction of the velocity—clockwise.
b. Neither field needs to be changed.
34. Both the galvanometer and the electric motor use
a loop of wire positioned between the poles of a
permanent magnet. When a current passes through
the loop, the magnetic field of the permanent magnet
exerts a force on the loop. The loop in a galvanometer
cannot rotate more than 180°. The loop in an electric
motor rotates through many 360° turns. The motor’s
split-ring commutator allows the current in the loop to
reverse as the loop becomes vertical in the magnetic
field, ­enabling the loop to spin in the magnetic field.
Check Your Progress
31. Motors Explain how electric motors use
magnets to convert electrical energy to
mechanical energy.
32. Magnetic Forces Imagine that a current-carrying wire is perpendicular to Earth’s magnetic
field and runs east-west. If the current is east,
in which direction is the force on the wire?
33. Synchrotrons In a synchrotron, magnetic
fields bend particle beams into segments of a
circle, and electric fields accelerate the beams.
a. A beam of protons circulates in a clockwise
direction. In what direction must the magnetic field be oriented? In what direction
must the electric fields be oriented?
The galvanometer measures unknown currents; the
electric motor has many uses.
35. Not necessarily; if the coil is already in rotation, then
­rotational inertia will carry it past the point of zero
torque. It is the coil’s acceleration that is zero, not the
velocity.
36. 28 kΩ
37. Because the force is attractive, the currents are in the
same direction. That is, an up current in the first wire
creates a magnetic field that intersects the second
wire. If the current in the second wire is in the same
direction, the force on it will pull the wires together.
Figure 21 Powerful electromagnets inside the LHC tunnel provide the uniform
magnetic field that makes charged particles move in a circular path.
b. If a beam of negatively charged antiprotons
is to circulate in a counterclockwise direction, must the direction of the magnetic
field be changed? Must the direction of the
electric fields be changed?
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36. Resistance A galvanometer requires 180 μA
for full-scale deflection. When it is used as a
voltmeter, what total resistance of the meter
and the multiplier resistor is needed for a
5.0-V full-scale deflection?
37. Critical Thinking Two current-carrying wires
move toward each other when they are
placed parallel to each other. Compare the
directions of the two currents. Explain your
reasoning.
Module 20 • Magnetism
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INTERACTIVE CONTENT
Explore and Explain:
Synchrotrons
ADDITIONAL RESOURCE
GO ONLINE You might want to assign from the
Additional Resources the pre-made Lesson Check based
on key concepts and disciplinary core ideas, or you can
customize your own using the customization tool.
35. Motors When the plane of an armature in a
motor is perpendicular to the magnetic field, the
forces do not exert a torque on the coil. Does
this mean that the coil does not rotate? Explain.
Go online to follow your personalized learning path to review, practice,
and reinforce your understanding.
Lesson Check: Applying
Magnetic Force
Formative Assessment: Lesson Check
34. Galvanometers Compare the diagram of a
galvanometer in the image on the right in
Figure 17 with the electric motor in Figure 19.
How is the galvanometer similar to an electric
motor? How is it different?
Chapter: 20
05:25PM
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Vocabulary Flashcards:
Applying Magnetic Force
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iStockphoto/Getty Images
32. up away from the surface of Earth
Synchrotrons Because the direction of
force is always perpendicular to a charged
particle’s velocity in a magnetic field,
magnets can be used to direct a charged
particle’s path. For example, accelerating
particles in a synchrotron, such as the
Large Hadron Collider (LHC), move in a
circle as they maintain their velocity at
right angles to a uniform magnetic field.
You can see several segments of the
27-km-long tunnel housing the LHC in
Figure 21. As the particles gain speed, the
magnetic field in the tunnel is increased
to keep the radius of the circle constant.
Additional magnets provide horizontal
and vertical forces to focus the beam.
Additional segments along the LHC
tunnel add fixed amounts of energy that
accelerate the particles.
iStockphoto/Getty Images
31. An armature in a magnetic field rotates 360° as a
split-ring commutator changes the direction of current,
producing mechanical energy.
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Module 20: Engineering & Technology
Accelerating the Solution
ENGINEERING & TECHNOLOGY
Purpose
Accelerating a Solution
For nearly a century, viewers with scrutinizing eyes
have detected hints of another painting concealed
beneath French impressionist Edward Degas’
painting Portrait of a Woman. Now, with the help of
a particle accelerator, scientists have solved the
mystery. Hidden beneath the contemplative woman
in the painting is another picture of the same
woman, painted seven years earlier.
Portrait of a Woman
Degas painted Portrait of a Woman in the late 1870s.
The model is tentatively identified as French model
Emma Dobigny. As time wore away some of the oil
paint from Degas’ canvas, the faint outline of another
face became visible beneath the painting. Recently,
Australian scientists used a type of particle accelerator called a synchrotron (similar to the Large Hadron
Collider) to reveal the original painting of the model
Dobigny.
Synchrotron Technology
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UPPA/Photoshot/Newscom
How did scientists use the synchrotron to “look”
beneath the top layers of paint without ruining the
completed painting? They employed a technique
called high-resolution scanning X-ray fluorescence
(XRF), which uses a beam of radiation to excite atoms,
causing them to emit X-ray photons. Each element’s
photons have a unique wavelength, enabling scientists to create elemental and scatter maps.
Scientists in the Netherlands are using special techniques
to uncover an earlier painting that was later painted over
by Vincent van Gogh.
The scans of Degas’ painting revealed the presence
of eleven element maps, including calcium, chromium, manganese, iron, cobalt, nickel, copper, zinc,
arsenic, barium, and mercury. Scientists reconstructed colors by inferring the pigments of paint
based on the elemental maps. When two or more
elements were located in the same area, scientists
were able to better identify the color used by Degas.
The elemental maps from XRF are composed of
millions of pixels. These high definition imaging
scans are used to make a “false” color representation of the hidden picture. Instead of seeing what the
naked eye sees, false color representation most
often incorporates the visible light spectrum and the
electromagnetic spectrum. When these elemental
map images were layered on top of each other, they
formed an image behind the painting of Dobigny’s
older picture.
ASK QUESTIONS TO CLARIFY
CCC
Write three questions that you have about XRF and
how it was used to reveal Degas’ hidden painting.
Use print or online sources to find answers to your
questions. Share your questions and answers with
your class.
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Chapter: 20
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Students will understand that scientists used a synchrotron, a type of particle accelerator, to reveal an image hidden under the Edgar Degas painting Portrait of a Woman.
Through a technique called high-resolution scanning X-ray
fluorescence (XRF) with a synchrotron, scientists created
elemental and scatter maps. When these maps were layered on top of each other, they revealed a different image
of the same woman who appears in the final painting.
Guiding Questions
Ask: Why do you think Degas made a second painting on
top of the first? Sample answer: He was unhappy with the
first painting and did not want to waste the canvas.
Tell students that reusing canvases was fairly common
during these times. It is estimated that up to one third of
Van Gogh’s works have hidden paintings. Usually a neutral-base layer was applied to provide a blank canvas for a
new painting, but Degas apparently skipped this step in his
Portrait of a Women.
Background
The painting under Portrait of a Woman is rotated 180
degrees from the final painting. Because it is upside down,
the lines of the woman’s face are located in the area of the
cheek of the woman in the final painting. Degas used very
thin layers of paint in the final painting and that because
oil paint becomes less opaque over time, the image of the
woman underneath has become more visible.
XRF has been used to reveal other hidden paintings, including the first major investigation that found the face of a
woman beneath Vincent Van Gogh’s Patch of Grass.
Scientists think that XRF technology will provide art historians with much added information about artists and their
paintings, allowing them to study artists’ methods and how
their techniques evolved over time.
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ASK QUESTIONS TO CLARIFY
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CCC
One option you might use to share students’ work with
the class is to make a game. Have students write their
­questions and answers on individual slips of paper. Divide
the class in half. Have the groups compete to correctly
­answer as many questions as possible.
Module 20 • Engineering & Technology
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Module 20: Study Guide
Review and Connect
Use the following tools to help students review the
content in this Module and to connect to the broader
topics of the Unit.
MODULE 20
STUDY GUIDE
GO ONLINE study with your Science Notebook.
Lesson 1 UNDERSTANDING MAGNETISM
Driving Question Board
Revisit the DQB and have students determine what
questions they can answer with their new knowledge.
At this point, they should be able to answer the Module
Encounter the Phenomenon Question.
Summary Table
As a class, review the Summary Table. If you do any endof-module activities, add them to the table.
Module Vocabulary Practice
Students can use the Module Vocabulary Practice to
review key terms.
LearnSmart® is an adaptive learning tool tailored to
the unique needs of each student. Have students use
LearnSmart® for review, to practice for assessment, and to
monitor the progress of their learning.
• All magnets have north poles and south poles and are surrounded by magnetic fields.
• Ferromagnetic materials become magnetic when their domains
are in alignment with each other.
• Magnetic fields are vector quantities because they have direction
and magnitude. They exist in any region in space where a magnet
would experience a force. Magnetic fields can be represented by
field lines, which exit from a north pole and enter at a south pole,
forming closed loops.
N
S
B
• A magnetic field exists around any current-carrying wire. The
magnetic field around a coil of wire is proportional to the number
of loops in the coil because the individual fields of the loops are
in the same direction.
Lesson 2 APPLYING MAGNETIC FORCES
• When a current-carrying wire is placed in a magnetic field, a force
is exerted on the wire that is perpendicular to both the field and
the wire.
• The force on a current-carrying wire in a magnetic field is proportional to the current times the length of the wire times the field
strength times the sine of the angle between the current and the
magnetic field.
• galvanometer
• electric motor
• armature
F = ILB(sin θ )
• An electric motor consists of a coil of wire in a magnetic field.
When there is current in the coil, the coil rotates as a result of the
force on the wire in the magnetic field. Complete 360° rotation is
achieved by using a split-ring commutator to switch the direction
of the current in the coil as the coil rotates.
• The force that a magnetic field exerts on a moving charged
particle depends on the charge of the particle, the velocity of the
particle, the strength of the magnetic field, and the angle between
the directions of the velocity and the field. The direction of the
force is perpendicular to both the field and the particle’s velocity.
F = qvB(sin θ)
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Chapter: 20
ADDITIONAL RESOURCE
Module 20 • Study Guide
polarized
domain
magnetic field
magnetic flux
solenoid
electromagnet
B
Module Vocabulary Practice:
Magnetism
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•
•
•
•
•
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REVISIT THE PHENOMENON
THREE-DIMENSIONAL THINKING
Claim, Evidence, Reasoning
Module Wrap-Up
Have students review the evidence they collected in
their Science Journals and the class Summary Table. If
students found evidence that contradicts their claims, their
claims are likely incorrect. Encourage students to use the
evidence they recorded to revise their claims.
REVISIT THE PHENOMENON
What makes this
electromagnet stronger
than a typical refrigerator
magnet?
CER
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Module Wrap-Up
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THREE-DIMENSIONAL THINKING
STEM UNIT PROJECT
Claim, Evidence, Reasoning
Explain Your Reasoning Revisit the claim you made when you encountered the
phenomenon. Summarize the evidence you gathered from your investigations and
research and finalize your Summary Table. Does your evidence support your claim? If not,
revise your claim. Explain why your evidence supports your claim.
Performance Task
Check in with students on their progress with their Unit
Projects. Encourage them to apply what they have learned
in the module to the project.
STEM UNIT PROJECT
Now that you’ve completed the module, revisit your STEM unit project. You will
summarize your evidence and apply it to the project.
GO FURTHER
Data Analysis Lab
Do magnets obey an inverse square law?
The repulsive force between two magnets was measured and found
to depend on distance, as given in the table.
Stockbyte/Getty Images
Separation
(cm)
Force
(N)
Separation
(cm)
1.0
3.93
2.2
0.011
1.2
0.40
2.4
0.0076
GO FURTHER
Go Further presents another opportunity for students to
practice making claims by analyzing information and data
and supporting their claims with evidence and reasoning.
Force
(N)
1.4
0.13
2.6
0.0053
1.6
0.057
2.8
0.0038
1.8
0.030
3.0
0.0028
2.0
0.018
Data Analysis Lab
Do magnets obey an inverse square law?
CER Analyze and Interpret Data
1. Plot the force as a function of distance.
2. Claim Does this force follow an inverse square law?
3. Evidence and Reasoning Defend your claim using your graph.
CER Analyze and Interpret Data
Module 20 • Magnetism
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1.
4.0
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ADDITIONAL RESOURCE
CER: Magnetism
Chapter: 20
05:25PM
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3.0
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Go Further: Do magnets
obey an inverse square law?
F (N)
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2.0
1.0
0.0
ADDITIONAL RESOURCE
Module Test: Magnetism
1.0
1.4
1.8
2.2
2.6
3.0
d (cm)
2. No
3. Students should use their graphs and calculations to
explain their reasoning and justify their claims.
Summative C24-07A-865893_A
Assessment: Module Test
GO ONLINE You might want to assign from the
Additional Resources the pre-made Module Test based
on key concepts and disciplinary core ideas, or you can
customize your own using the customization tool.
Module 20 • Magnetism
567
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