Download answer_key - Northside Middle School

TEACHER RESOURCES
Answer Key
Directed Reading A
27. Answers may vary. Sample answer:
Scientists think that Earth’s magnetic field is
made of electric charges in Earth’s core,
which is made mostly of iron and nickel.
The inner core is solid because of great
pressure. The outer core is liquid, and the
charges move as the liquid moves. As
charges move, a magnetic field is formed.
28. aurora
SECTION: MAGNETS AND
MAGNETISM
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
magnet
magnetic poles
north pole
south pole
magnetic force
magnetic field
magnetic forces
magnetic forces
magnetic forces
magnetic fields
magnetic fields
magnetic fields
B
D
C
B
Sample answers: dropping a magnet; hitting
it too hard; putting the magnet in a strong
magnetic field opposite to its own;
increasing its temperature
Sample answer: You may magnetize
something made of iron, cobalt, or nickel by
rubbing in one direction with one pole of a
magnet.
Sample answer: A magnet’s domains are
like tiny magnets, each with a north and a
south pole. So, even small pieces of magnets
have poles.
C
B
A
D
Answers may vary. Sample answer:
Magnets point to the north because Earth is
one giant magnet.
Answers may vary. Sample answer: A
compass needle tip that points to the north is
the north pole of its compass. So, it points to
the south pole of a magnet.
Answers may vary. Sample answer: A
compass needle points to Earth’s geographic
north because Earth’s magnetic south pole is
near Earth’s geographic North Pole.
SECTION: MAGNETISM FROM
ELECTRICITY
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
B
A
B
A
Hans Christian Oersted and André-Marie
AmpE8re
B
C
B
A
B
B
C
Answers may vary. Sample answer:
Electromagnets attract things only when a
current exists in the wire. When there is no
current, the electromagnet is turned off.
C
D
B
A
SECTION: ELECTRICITY FROM
MAGNETISM
1. Both Henry and Faraday worked to solve the
question of whether a magnetic field could
make an electric current.
2. electromagnetic induction
3. Answers may vary. Sample answer: As long
as the battery was connected, the
galvanometer measured no electric current.
Electric current was made only when the
magnetic field was changing.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
91
Electromagnetism
TEACHER RESOURCES
Directed Reading B
4. Answers may vary. Sample answer: A
greater electric current is induced if you
move the magnet faster through the coil,
because the magnetic field is changing
faster. The current will also be greater if you
add more loops of wire.
5. B
6. C
7. Answers may vary. Sample answer: coil of
wire that rotates; permanent magnet or
electromagnet on either side of the coils; slip
rings attached to the ends of the wires of the
coil; electric current leaves the generator
when the slip rings touch a pair of brushes.
8. Answers may vary. Sample answer:
Generators in power plants have many coils
of wire instead of just one. Also, in most
power plants the magnet is turned instead of
the coils being turned.
9. Answers may vary. Sample answer: thermal
energy from a nuclear reaction, or from
burning fuel, such as coal or gas; wind
energy used to turn turbines; falling water in
a hydroelectric plant
10. 2
11. 1
12. 4
13. 3
14. C
15. Answers may vary. Sample answer: The
number of loops in the primary and
secondary coils of a transformer determines
whether the transformer increases or
decreases the voltage.
16. Answers may vary. Sample answer: A stepup transformer increases voltage and
decreases current. Power plants step up
voltage thousands of times to lower power
loss as energy is sent.
17. Answers may vary. Sample answer:A stepdown transformer decreases voltage and
increases current. Power distribution centers
step down the voltage that comes from the
power plant, and a transformer near your
home steps down the energy further before
the electric current reaches your house.
SECTION: MAGNETS AND
MAGNETISM
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
A
B
A
north pole
south pole
magnetic force
magnetic poles
magnetic field
magnetic field lines
A
B
D
D
D
A
C
B
A
C
A
C
D
B
SECTION: MAGNETISM FROM
ELECTRICITY
1.
2.
3.
4.
5.
6.
7.
8.
A
C
B
C
D
D
B
A
9.
10.
11.
12.
13.
14.
15.
A
D
B
C
A
B
A
SECTION: ELECTRICITY FROM
MAGNETISM
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
B
C
B
A
C
B
A
C
B
B
A
C
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
92
Electromagnetism
TEACHER RESOURCES
Vocabulary an d Section
Summary
4. Iron objects are magnetic if most of their
domains are aligned. If the domains are
randomly arranged, the objects aren’t
magnetic.
5. Temporary magnets are easy to magnetize
but lose their magnetization easily.
Permanent magnets are difficult to
magnetize but retain their magnetic
properties for a long time.
6. Auroras are most commonly seen near
Earth’s magnetic poles. Because Alaska and
Australia are close to the Earth’s magnetic
poles, people living in those places are more
likely to see auroras than are people living in
Florida and Mexico, which are far away
from the Earth’s magnetic poles.
7. Attach strong magnets to a small object so
that the north poles of the magnets point
downward. Place strong magnets on a table
so that the north poles point upward. When
the object is placed above the magnets on
the table, the magnetic force between the
magnets will push the object up and make it
appear to float in air.
8. Sample answer: I would not expect to see
auroras on the moon. Because it has a cool,
solid core, the moon would not have a
strong magnetic field to guide charged
particles from the sun. Because it has no
atmosphere, the moon has no gas atoms for
the charged particles to hit.
9. a magnetic south pole
10. The magnetic field is stronger at the bottom
of Earth (in Antarctica) than it is in the
middle of Earth (in Mexico) because a
magnetic pole is located in Antarctica, so the
magnetic field lines are closer together at the
bottom of Earth than they are in the middle
of Earth.
SECTION: MAGNETS AND
MAGNETISM
1. magnet: any material that attracts iron or
materials containing iron
2. magnetic pole: one of two points, such as
the ends of a magnet, that have opposing
magnetic qualities
3. magnetic force: the force of attraction or
repulsion generated by moving or spinning
electric charges
SECTION: MAGNETISM FROM
ELECTRICITY
1. electromagnetism: the interaction between
electricity and magnetism
2. solenoid: a coil of wire with an electric
current in it
3. electromagnet: a coil that has a soft iron core
and that acts as a magnet when electric
current is in the coil
4. electric motor: a device that converts
electrical energy into mechanical energy
SECTION: ELECTRICITY FROM
MAGNETISM
1. electromagnetic induction: the process of
creating a current in a circuit by changing a
magnetic field
2. electric generator: a device that converts
mechanical energy into electrical energy
3. transformer: a device that increases or
decreases the voltage of alternating current
Section Review
SECTION: MAGNETS AND
MAGNETISM
1. Sample answer: A magnet will experience a
magnetic force when one of the magnet’s
magnetic poles interacts with the pole of
another magnet.
2. D
3. All magnets have two poles, exert magnetic
forces, and are surrounded by a magnetic
field.
SECTION: MAGNETISM FROM
ELECTRICITY
1. An electromagnet is a solenoid that has an
iron core, so an electromagnet has a stronger
magnetic field than the solenoid has.
2. D
3. The needle may deflect and not point north.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
93
Electromagnetism
TEACHER RESOURCES
7. The electric current in the transformer’s
primary coil makes the iron ring an
electromagnet. That electromagnet induces
an electric current in the secondary coil only
if the electromagnet’s magnetic field
changes. Direct current passing through the
primary coil will not change the
electromagnet’s magnetic field, so no
electric current will be produced in the
secondary coil.
8. You can rotate either the coil or the magnet
in a generator. In either case, there will be a
change in the magnetic field in the coil. The
changing magnetic field induces an electric
current in the wire.
4. An electric current induces a magnetic field.
A changing magnetic field can induce an
electric current.
5. The motor’s magnet exerts a force (up on
one side, down on the other) on the
armature, which causes the armature to
rotate.
6. Oersted’s conclusion that an electric current
induces a magnetic field led to the
development of electromagnets. A
galvanometer measures the interaction
between the magnetic field produced by an
electromagnet and the magnetic field of a
permanent magnet.
7. A solenoid is a coil of wire that carries
electric current. An electromagnet is a
solenoid that has an iron coil. An
electromagnet has a stronger magnetic field
than the solenoid has.
8. Sample answer: My friend is wrong. The
loops of an electromagnet must be loops of
wire, not ring magnets. The core of an
electromagnet must be made of iron. The
core in the image is a pencil.
Chapter Review
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
SECTION: ELECTRICITY FROM
MAGNETISM
1. An electric generator changes mechanical
energy into electrical energy through
electromagnetic induction. A transformer
changes the voltage of alternating current
through electromagnetic induction.
2. D
3. A generator usually rotates a coil of wire
through a magnetic field. This motion of the
wire through the magnetic field induces an
electric current in the wire.
4. A step-up transformer has more loops in its
secondary coil than it has in its primary coil.
A step-down transformer has more loops in
its primary coil than it has in its secondary
coil.
5. (20,000V/5,000loops) 3 500loops 5 2,000V
6. (120V/3,000loops) 3 1,500loops 5 60V
12.
13.
14.
15.
magnetic pole
electric generator
Electromagnetic induction
electromagnetism
A
D
C
C
D
C
Auroras are usually seen near Earth’s
magnetic poles. Earth’s magnetic poles are
located near Earth’s geographic North and
South Poles.
The function of a generator is opposite of
the function of an electric motor. A
generator converts mechanical energy into
electrical energy, and an electric motor
converts electrical energy into mechanical
energy.
Some pieces of iron are more magnetic than
others because the domains of the magnetic
pieces are more aligned. The domains of the
less magnetic pieces are randomly arranged.
1,200 V 320 5 24,000 V
An answer to this exercise can be found at
the end of the Teacher Edition.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
94
Electromagnetism
TEACHER RESOURCES
16. The electric current is produced by
electromagnetic induction. The gray ring is a
magnet, and when it spins, it creates a
changing magnetic field in the coils of wire.
An electric current is induced in the wire
and lights the bulb.
17. Electromagnets are used instead of
permanent magnets because electromagnets
can be easily turned off. When the
electromagnets are turned off, the fire doors
close.
18. Electromagnet (c) is strongest because it has
an iron core and the largest current. Solenoid
(a) is weakest because it has no iron core
and the smallest current.
3. Answers may vary. Sample answer:
Critical Thinking
MAGIC MAGNET MISFORTUNE
1. Answers may vary. Sample answer: The
electromagnet in the glove did not have
enough magnetic force to attract more than
20 paper clips.
2. Answers may vary. Sample answer: The
glove trick would not have worked with
pennies because pennies are made of copper,
a nonmagnetic material.
3. Answers may vary. Sample answer: The
Electro-Magneto Glove probably contains a
coil of current-carrying wire wrapped
around an iron core; the coil is attached to
an electrical cell.
4. Answers may vary. Sample answer: The
magician should connect a higher voltage
cell to his Electro-Magneto Glove or wrap
more coils around the core.
5. Answers may vary. Sample answer: The
magician was not aware that he needed to
use opposite magnetic poles in order for the
magnets to attract one another.
6. Answers may vary. Answers must be
supported by an understanding of
magnetism, electromagnetism, and how an
electromagnet is constructed.
Reinforcement
PLANET LODESTONE
1. Answers may vary. Sample answer: If the
planet had a liquid core that contained
mostly iron and nickel, like Earth’s, then the
planet would probably have magnetic
properties.
2. Answers may vary: Sample answer: When a
bar magnet is suspended on a string in a
magnetic field, the magnet will always point
in the same direction. The north pole of the
magnet will point to the south magnetic pole
of the planet.
3. Sample answer: No; on Earth, geographic
north is really a magnetic south pole and
geographic south is really a magnetic north
pole. So a magnet that points north on
Lodestone would point south on Earth.
A MAGNETIC TIME
1-2 Lines should match up as follows: Hans
Christian Oersted | after many experiments,
concluded that an electric current produces a
magnetic field | 1820; Michael Faraday,
Joseph Henry | found that a changing
magnetic field could induce an electric
current | 1831; Greeks | found a mineral
called magnetite, which attracts ironcontaining objects | 2000 years ago; William
Gilbert | proposed that the Earth is one giant
magnet | 1600
Section Quizzes
SECTION: MAGNETS AND
MAGNETISM
1.
2.
3.
4.
D
D
B
D
5. B
6. A
7. C
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
95
Electromagnetism
TEACHER RESOURCES
SECTION MAGNETISM FROM
ELECTRICITY
1.
2.
3.
4.
B
C
C
B
too close to another magnet
12. Answers may vary. Sample answer: A
solenoid is a coil of wire with an electric
current in it. An electromagnet is a solenoid
that has a soft iron core and that acts as a
magnet when an electric current is in the
coil.
13. Answers may vary. Sample answer:
Magnetic fields in both solenoids and
electromagnets are strengthened by
increasing the number of loops in their
14. Answers may vary. Sample answer:
Magnetic material could be useful when the
Monarch butterflies migrate from one place
to another. The magnetic material inside
their bodies would align with Earth’s
magnetic field and allow the butterflies to
sense which direction is north as they fly.
15. Answers may vary. Sample answer: The
discovery of magnetism and invention of the
compass made it possible for sailors to go
beyond the sight of land, and to sail at night,
or in cloudy weather when the position of
the stars could not be seen.
16. Answers may vary. Sample answer: The
alternating current in the primary coil
induces a changing magnetic field. The
changing magnetic field induces a current in
the secondary coil.
17. Answers may vary. Sample answer: Earth’s
magnetic poles are the points on Earth’s
surface where its magnetic forces are the
strongest. The north pole of a magnet is
attracted to the magnetic south pole of Earth.
Therefore, Earth’s magnetic south pole is
near Earth’s geographic North Pole; and
Earth’s magnetic north pole is near Earth’s
geographic South Pole.
18. Answers may vary. Sample answer: The
lines in the figure of Earth represent
magnetic field lines. They map the strength
of the magnetic force and show the shape of
the magnetic field around Earth, similar to
field lines around a bar magnet
5. D
6. C
7. A
SECTION: ELECTRICITY FROM
MAGNETISM
1. A
2. C
3. C
4. B
5. C
6. A
Chapter Test A
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
J
A
H
D
G
I
B
C
C
B
D
A
A
C
D
B
C
A
D
B
C
C
B
Chapter Test B
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
transformer
magnet
electromagnetic induction
electromagnetism
electric motor
electric generator
C
C
D
A
Answers may vary. Sample answer:
dropping the magnet, hitting the magnet too
hard, and getting the magnet
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
96
Electromagnetism
TEACHER RESOURCES
Chapter Test C
Vocabulary Activity
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
1. magnetic force
2. poles
3. galvanometer
4. electric motor
5. electromagnet
6. Oersted
7. induction
8. ferromagnet
9. Faraday
10. maglev
11. domain
12. magnetic field
13. generator
14. solenoid
15. transformer
16. magnet
Hidden word: electromagnetism
C
B
D
A
C
A
C
B
A
B
solenoid
electromagnet
magnetic field
electric current
B
C
B
SciLinks Activity
Standardized Test
Preparation
1. Answers may vary. Pictures drawn by
students should look like any of the Maglev
trains on the several links related to Maglev
trains at www.scilinks.org, keyword
HSM0483.
2. Answers may vary. Sample answer: When
two magnets are put together, opposite poles
attract and similar ones repel.
3. Answers may vary. Sample answer:
Magnets in the track or guideway control
both the levitation of the cars and the train’s
speed.
4. Answers may vary. Sample answer: There’s
no friction between the train and the track.
READING
Passage 1
1. D
2. I
Passage 2
1. B
2. I
INTERPRETING GRAPHICS
1. D
2. F
3. B
Performance-Based
Assessment
MATH
1.
2.
3.
4.
C
I
B
G
ANALYZE RESULTS
7. Sample answer: Because the solenoid
generates a magnetic field along its length,
the compass needle should point away from
the tube.
8. Answers will vary. Sample answer: The
needle was deflected from true north.
9. Because the iron rod will become
magnetized by the solenoid’s magnetic field,
the two magnets will combine in strength.
This should make the compass needle
deflect much more strongly than before.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
97
Electromagnetism
TEACHER RESOURCES
Model of Earth’s Magnetic
Field
DRAW CONCLUSIONS
10. Sample answer: Yes. The needle moved
much faster this time.
11. If the tube were reversed, the needle would
not move. Because the B end of the solenoid
is the “south” end, the A end must be the
“north” end. Therefore the needle would be
attracted to it and would not move.
PROCEDURE
3. Sample answer: The filings line up and look
somewhat like the wings of a butterfly. A lot
of filings are gathered near each end of the
magnet and are pointing away from the
magnet. On either side of the magnet, the
filings form large loops from one end of the
magnet to the other.
Build a DC Motor
ANALYZE THE RESULTS
Electromagnets
1. The motor did not always continue to spin in
the direction in which it started spinning.
Switching the battery connections caused it
to spin in the opposite direction.
2. The motor was affected by switching the
battery connections because the direction of
the electric current in the coil was reversed.
This change reversed the magnetic field,
which caused the motor to spin in the
opposite direction.
3. Solar panels would replace the battery as the
energy source.
PROCEDURE
4. Several paper clips are picked up, and they
fall off when the wire is detached.
5. the ability to turn the magnet on and off
Magnetic Mystery
ANALYZE THE RESULTS
1. Drawings may vary. Placement of the
magnet should match the field lines.
APPLYING YOUR DATA
The poles of a magnet cannot be identified by
looking at the field lines. A navigation compass
or a magnet with labeled poles could be used to
identify the magnet’s poles.
DRAW CONCLUSIONS
4. Electric cars do not burn gasoline, so they
do not produce exhaust gases that are
components of air pollution.
5. Electric cars are not ideal because the
batteries run down and have to be replaced
(which means more waste) or recharged
(which requires more electrical energy).
Also, batteries don’t generate a lot of energy
relative to their weight, so electric cars
aren’t very powerful.
6. Accept all reasonable answers. Sample
answer: The model could be used to help
design a hair dryer. You could attach various
fans to the armature (spinning part) to see
how well they work. Also, different
combinations of batteries and coils could be
tested to see if a battery-powered hair dryer
would be powerful enough.
7. Answers will vary. Accept all reasonable
answers that include items that use a
spinning motion.
Electricity from Magnetism
ANALYZE THE RESULTS
1. The faster the magnet moves, the greater the
electric current is.
2. When the direction of the magnet’s motion
is reversed, the direction of the current is
also reversed.
3. Answers will depend on the hypothesis
written in step 2.
DRAW CONCLUSIONS
4. Electric current would not be generated
because the circuit is not complete.
5. A stationary magnet could produce an
electric current if the wire moves, as in step
6.
6. The mechanical energy of the moving wire
or magnet is converted into electrical
energy.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
98
Electromagnetism
TEACHER RESOURCES
7. Sample answer: The three requirements for
generating electricity from magnetism are a
magnet, a complete circuit, and motion
between the two.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
99
Electromagnetism