Magnets
Electricity and Magnetism Magnetism Key Concepts • What causes a magnetic force? • How are magnets and magnetic domains related? • How are electric currents and magnetic fields related?
What do you think? Read the three statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind. Before
Statement
After
4. Every magnet has one magnetic pole. 5. Earth is magnetic but is not a magnet. 6. A magnet moving within a wire loop produces
an electric current.
Reading Check
1. Recognize Why is the metal cobalt a magnetic material?
256
Electricity and Magnetism
What is a magnet? How many magnets could you find in your house? You might think of the magnets holding notes on your refrigerator. However, some magnets are not so obvious. Did you know that your television, DVD player, and computer all use magnets? Credit cards use magnetized strips to hold personal information. So, what is a magnet? Magnets attract some objects, such as paper clips, but not others, such as pieces of paper. A magnet is an object that attracts iron and other materials that have magnetic qualities similar to iron. A magnet attracts paper clips and some nails because they contain iron. Magnets also attract other metals, such as nickel, cobalt, and alnico, an aluminum-nickel-cobalt alloy. Any material that a magnet attracts is a magnetic material.
Magnetic Fields and Magnetic Forces An invisible electric field surrounds an electrically charged object. In the same way, an invisible magnetic field surrounds a magnet and an electric current. Even though magnetic fields are invisible, they can be detected by the forces they apply. A magnetic force is a push or a pull a magnetic field applies to either a magnetic material or an electric current.
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Identify the Main Ideas Write a phrase beside each paragraph that summarizes the main point of the paragraph. Use the phrases to review the lesson.
Seeing a Magnetic Field A magnet’s magnetic field applies a magnetic force to a magnetic material even when the magnet and the magnetic material do not touch. A magnetic field and its force are stronger closer to the Magnetic Field magnet and weaker farther away from the magnet. The figure at right helps you to visualize a magnetic field. Iron is a magnetic material. When iron filings are sprinkled around a magnet, the filings will line up with the magnet’s magnetic field. The iron filings form a pattern of curved lines. These curved lines are the magnet’s magnetic field lines.
N
Visual Check
2. Summarize How can iron filings illustrate a magnetic attraction?
S
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Magnetic Poles Magnets are made in many sizes and shapes. However, all magnets have something in common. Every magnet has two magnetic poles. One pole of a magnet is called the magnetic north pole. The other pole is called the magnetic south pole. The magnetic poles are the two places on a magnet where the magnetic field lines are closest together. This is also where the magnetic field applies the strongest force. Magnetic field lines point away from the magnet’s magnetic north pole and toward the magnet’s magnetic south pole. For a bar magnet, as shown in the figure above, the ends of the magnet are the magnetic poles.
Magnetic Poles and Magnetic Forces The forces that magnets apply to each other depend on which magnetic poles are near each other. If two magnetic south poles or two magnetic north poles are close to each other, the magnets repel, or push away from each other. In disc magnets, this repulsion causes one magnet to “float” on the invisible magnetic field of another disc magnet. If a magnet’s magnetic north pole is near another magnet’s magnetic south pole, the magnets attract each other. This attraction causes the magnets to come together. In other words, similar poles repel, opposite poles attract.
Reading Essentials
Reading Check
3. Name What do all magnets have in common?
Key Concept Check
4. Explain What causes the forces applied by magnets?
Electricity and Magnetism
257
Earth as a Magnet How does a magnetic compass help you find Earth’s geographic North Pole? A compass needle is a small bar magnet. Like all magnets, a magnetic field surrounds a compass needle.
Reading Check
5. State Which of Earth’s geographic poles is about in the same location as Earth’s magnetic south pole?
Flowing molten iron and nickel in Earth’s outer core create a magnetic field around Earth. Therefore, Earth has a magnetic north pole and a magnetic south pole. Recall that the opposite poles of two magnets attract each other. Thus, the compass needle’s magnetic north pole points toward Earth’s magnetic south pole. This means that Earth’s magnetic south pole is near Earth’s geographic North Pole.
Magnets Why do magnets attract only some materials? Remember, all matter is made of atoms. A magnetic field surrounds each atom. In some materials, atoms are grouped in magnetic domains. A magnetic domain is a region in a magnetic material in which the magnetic fields of the atoms all point in the same direction. The magnetic fields of the atoms within a domain combine into a single field around the domain. Think of a magnetic domain as a tiny magnet within a material.
Nonmagnetic Materials
Magnetic
Nonmagnetic
Key Concept Check
6. Compare How are magnets and magnetic domains related?
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Electricity and Magnetism
Magnetic Materials In some materials, such as iron and steel, atoms are grouped in magnetic domains. These materials are called magnetic materials. However, not all magnetic materials are magnets. For example, the magnetic fields of the domains of a steel nail point in different directions. The magnetic fields of these domains cancel out the magnetic effects of each other. Here, the magnetic material is not a magnet. A magnetic material becomes a magnet as the magnetic fields of the material’s magnetic domains line up to point in the same direction. The aligned magnetic fields of the domains combine to form a single magnetic field around the entire object. In this case, the magnetic material is a magnet.
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Create a horizontal two-tab book and use it to describe and to collect examples of magnetic and nonmagnetic materials.
Most materials, including aluminum and plastic, do not have atoms grouped in magnetic domains. The atoms point in many different directions. The random magnetic fields cancel out the magnetic effects of each other. These nonmagnetic materials cannot be made into magnets.
Temporary and Permanent Magnets Some magnetic materials lose their magnetic fields quickly. Other materials keep their magnetic fields for a long time. How long a magnet remains a magnet depends partly on the material from which it is made. Soft magnetic materials are not soft to the touch. They are called soft because they quickly lose their magnetic fields. Materials that keep their magnetic fields for long periods of time are hard magnetic materials.
Temporary Magnets Placing a soft magnetic material, such
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
as iron, in a strong magnetic field causes the material’s magnetic domains to line up. Temporary Magnet a) This makes the material a magnet. When the material is moved away from the magnetic field, its domains return to their random positions, and the material is no longer a magnet. In part a b) of the figure to the right, the nail is not a magnet. However, in part b, the nail is a magnet. This happens because the magnet’s magnetic field causes the magnetic field of the nail’s magnetic domains to line up. Thus, the nail becomes a magnet. The nail is a temporary magnet because it attracts other magnetic materials only if it is in the magnetic field of another magnet.
Permanent Magnets Hard magnetic materials are mixtures of iron, nickel, and cobalt combined with other elements. When a hard magnetic material is placed in an extremely strong magnetic field, the material’s magnetic domains align and lock into place.
Reading Check
7. Name the two types of magnetic materials.
Visual Check
8. Identify Circle the nail that shows magnetic domains in alignment.
Reading Check
9. Explain Why do soft magnetic materials make temporary magnets?
When a magnet made in this way is removed from the strong magnetic field, the object remains a magnet permanently, unlike a temporary magnet. Lodestone, a naturally occurring permanent magnet, is found in Earth’s crust. Other permanent magnets can be made with electric devices called magnetizers.
Reading Essentials
Electricity and Magnetism
259
Combining Electricity and Magnetism
Reading Check
10. Define What is electromagnetism?
In 1820, Danish scientist Hans Christian Ørsted noticed that a compass needle moved when a nearby electric current was switched on. He was convinced there was a relationship between electricity and magnetism. Today, we call this relationship electromagnetism. Almost all the electrical devices in your home, if they use an electric motor, depend on electromagnetism.
Magnetic fields produce electric currents. Recall that a generator is a machine that produces an electric current. As shown in the figure below, you can make a simple generator. All you need is a small wire coil connected in a circuit and a magnet. When you move the magnet through the center of the coil, the magnet’s magnetic field moves over the loops of the coil. The moving magnetic field forces an electric current to flow through the circuit. When the magnet stops moving, the current stops, too.
How a Generator Works –
Visual Check
0
+
N
S
Motion of magnet
Key Concept Check
12. Summarize How do electric currents and magnetic fields interact?
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Electricity and Magnetism
More complex generators use wire coils with more loops and stronger magnets that rotate in place. You can produce an electric current by using a hand-cranked generator to rotate a magnet within a small wire coil. The hand-cranked generator produces only a small amount of electric current. Huge generators use coils with several kilometers of wire and giant magnets to produce the electric current that is supplied to homes, buildings, and cities.
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
11. Identify Circle the magnetic field.
Electric currents produce magnetic fields. Recall that some magnetic materials become temporary magnets when placed in the magnetic field of another magnet. There is another type of temporary magnet that is very common and useful.
N S
13. Draw Trace the flow of electric current in the wire.
S
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Visual Check
N
S N
S N
Hans Ørsted discovered that a Magnetic Field magnetic field surrounds a + current-carrying wire. The magnetic field is shown as a series of circles in the figure to the right. If a current-carrying wire is wound into a coil, the magnetic field becomes stronger. When a soft magnetic material is placed within the coil, the – magnetic field becomes even stronger. A temporary magnet made with a current-carrying wire coil wrapped around a magnetic core is an electromagnet.
Electromagnets are useful because they can be controlled in ways other magnets cannot. First, an electromagnet’s magnetic field can be turned off and on. Turning off the electric current in the coil turns off the magnetic field. Second, the north and south poles of the electromagnet reverse when the current reverses. And finally, the strength of an electromagnet can be controlled with the number of loops in the coil and the amount of electric current in the coil.
Reading Check
14. Summarize How can the strength of an electromagnet be controlled?
Reading Essentials
Electricity and Magnetism
261
Mini Glossary electromagnet: a temporary magnet made with a current-
magnetic force: a push or a pull a magnetic field applies to
carrying wire coil wrapped around a magnetic core
either a magnetic material or an electric current
magnet: an object that attracts iron and other materials that
magnetic material: any material that a magnet attracts
have magnetic qualities similar to iron
magnetic domain: a region in a magnetic material in which the magnetic fields of the atoms all point in the same direction
1. Review the terms and their definitions in the Mini Glossary. Write a sentence explaining how a magnetic material can become a magnet.
2. Use the graphic organizer to identify the two types of magnetic materials. Then state one similarity and one difference between the two types. Similarity
Difference
3. You hold two bar magnets close together; however, instead of sticking to teach other, they push apart. Explain why.
What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?
262
Electricity and Magnetism
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Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.
END OF LESSON
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Types of magnetic materials
PERIODIC TABLE OF THE ELEMENTS 1
1
Hydrogen 1
2
H
Gas
Hydrogen 1
Element Atomic number Symbol Atomic mass
Liquid
State of matter
H
Solid
1.01
Synthetic
1.01
2
3
4
5
6
7
Lithium 3
Beryllium 4
6.94
9.01
Sodium 11
Magnesium 12
22.99
24.31
Potassium 19
Calcium 20
Scandium 21
Titanium 22
Vanadium 23
Chromium 24
Manganese 25
Iron 26
Cobalt 27
39.10
40.08
44.96
47.87
50.94
52.00
54.94
55.85
58.93
Rubidium 37
Strontium 38
Yttrium 39
Zirconium 40
Niobium 41
Mo
Tc
Ruthenium 44
Rhodium 45
85.47
87.62
88.91
91.22
92.91
95.96
(98)
101.07
102.91
Cesium 55
Barium 56
Lanthanum 57
Hafnium 72
Tantalum 73
Tungsten 74
Rhenium 75
Osmium 76
Iridium 77
132.91
137.33
138.91
178.49
180.95
183.84
186.21
190.23
192.22
Francium 87
Radium 88
Actinium 89
Rutherfordium 104
Dubnium 105
Seaborgium 106
Bohrium 107
Hassium 108
Meitnerium 109
(223)
(226)
(227)
(267)
(268)
(271)
(272)
(270)
(276)
Li
Na
K
Rb
Cs
Fr
A column in the periodic table is called a group.
Be
3
Mg
Ca
Sr
Ba
Ra
Sc
Y
La
Ac
4
Ti
Zr
Hf
Rf
5
V
Nb
Ta
Db
6
Cr
7
Mn
Molybdenum Technetium 43 42
W
Sg
Re
Bh
9
8
Fe
Ru
Os
Hs
Co
Rh
Ir
Mt
The number in parentheses is the mass number of the longest lived isotope for that element.
A row in the periodic table is called a period.
Lanthanide series
Actinide series
Cerium 58
Praseodymium Neodymium Promethium 59 60 61
Samarium 62
Europium 63
Pr
Nd
Pm
140.12
140.91
144.24
(145)
150.36
151.96
Thorium 90
Protactinium 91
Uranium 92
Neptunium 93
Plutonium 94
Americium 95
232.04
231.04
238.03
(237)
(244)
(243)
Ce
Th
Pa
U
Np
Sm
Pu
Eu
Am
Metal
18
Metalloid Nonmetal
13
Recently discovered
14
11
17
16
He
4.00 Boron 5
Carbon 6
Nitrogen 7
Oxygen 8
Fluorine 9
Neon 10
10.81
12.01
14.01
16.00
19.00
20.18
Aluminum 13
Silicon 14
Phosphorus 15
Sulfur 16
Chlorine 17
Argon 18
26.98
28.09
30.97
32.07
35.45
39.95
B
10
15
Helium 2
12
C
Al
Si
N
O
P
S
F
Ne
Cl
Ar
Nickel 28
Copper 29
Zinc 30
Gallium 31
Germanium 32
Arsenic 33
Selenium 34
Bromine 35
Krypton 36
58.69
63.55
65.38
69.72
72.64
74.92
78.96
79.90
83.80
Palladium 46
Silver 47
Cadmium 48
Indium 49
In
Tin 50
Sn
Antimony 51
Tellurium 52
Iodine 53
Xenon 54
106.42
107.87
112.41
114.82
118.71
121.76
127.60
126.90
131.29
Platinum 78
Gold 79
Mercury 80
Thallium 81
Lead 82
Bismuth 83
Polonium 84
Astatine 85
Radon 86
195.08
196.97
200.59
204.38
207.20
208.98
(209)
(210)
(222)
Ni
Pd
Pt
Cu
Ag
Au
Ga
Zn
Cd
Hg
Darmstadtium Roentgenium Copernicium 110 111 112
Ds
Rg
Cn
(281)
(280)
(285)
Ge
Pb
Tl
Ununtrium 113
*
Uut
(284)
As
Sb
Bi
Se
Te
Po
Br
Uuq
(289)
*
Uup
(288)
*
Xe
I
At
Ununquadium Ununpentium Ununhexium 114 115 116
*
Kr
Rn
Ununoctium 118
*
Uuh
Uuo
(294)
(293)
* The names and symbols for elements 113-116 and 118 are temporary. Final names will be selected when the elements’ discoveries are verified. Gadolinium 64
Terbium 65
Dysprosium 66
Holmium 67
Erbium 68
Thulium 69
Ytterbium 70
Lutetium 71
157.25
158.93
162.50
164.93
167.26
168.93
173.05
174.97
Curium 96
Berkelium 97
Californium 98
Einsteinium 99
Fermium 100
Mendelevium 101
Nobelium 102
Lawrencium 103
(247)
(247)
(251)
(252)
(257)
(258)
(259)
(262)
Gd
Cm
Tb
Bk
Dy
Cf
Ho
Es
Er
Fm
Tm
Md
Yb
No
Lu
Lr
What do you think? Read the three statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind. Before
Statement
After
4. Every magnet has one magnetic pole. 5. Earth is magnetic but is not a magnet. 6. A magnet moving within a wire loop produces
an electric current.
Reading Check
1. Recognize Why is the metal cobalt a magnetic material?
256
Electricity and Magnetism
What is a magnet? How many magnets could you find in your house? You might think of the magnets holding notes on your refrigerator. However, some magnets are not so obvious. Did you know that your television, DVD player, and computer all use magnets? Credit cards use magnetized strips to hold personal information. So, what is a magnet? Magnets attract some objects, such as paper clips, but not others, such as pieces of paper. A magnet is an object that attracts iron and other materials that have magnetic qualities similar to iron. A magnet attracts paper clips and some nails because they contain iron. Magnets also attract other metals, such as nickel, cobalt, and alnico, an aluminum-nickel-cobalt alloy. Any material that a magnet attracts is a magnetic material.
Magnetic Fields and Magnetic Forces An invisible electric field surrounds an electrically charged object. In the same way, an invisible magnetic field surrounds a magnet and an electric current. Even though magnetic fields are invisible, they can be detected by the forces they apply. A magnetic force is a push or a pull a magnetic field applies to either a magnetic material or an electric current.
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Identify the Main Ideas Write a phrase beside each paragraph that summarizes the main point of the paragraph. Use the phrases to review the lesson.
Seeing a Magnetic Field A magnet’s magnetic field applies a magnetic force to a magnetic material even when the magnet and the magnetic material do not touch. A magnetic field and its force are stronger closer to the Magnetic Field magnet and weaker farther away from the magnet. The figure at right helps you to visualize a magnetic field. Iron is a magnetic material. When iron filings are sprinkled around a magnet, the filings will line up with the magnet’s magnetic field. The iron filings form a pattern of curved lines. These curved lines are the magnet’s magnetic field lines.
N
Visual Check
2. Summarize How can iron filings illustrate a magnetic attraction?
S
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Magnetic Poles Magnets are made in many sizes and shapes. However, all magnets have something in common. Every magnet has two magnetic poles. One pole of a magnet is called the magnetic north pole. The other pole is called the magnetic south pole. The magnetic poles are the two places on a magnet where the magnetic field lines are closest together. This is also where the magnetic field applies the strongest force. Magnetic field lines point away from the magnet’s magnetic north pole and toward the magnet’s magnetic south pole. For a bar magnet, as shown in the figure above, the ends of the magnet are the magnetic poles.
Magnetic Poles and Magnetic Forces The forces that magnets apply to each other depend on which magnetic poles are near each other. If two magnetic south poles or two magnetic north poles are close to each other, the magnets repel, or push away from each other. In disc magnets, this repulsion causes one magnet to “float” on the invisible magnetic field of another disc magnet. If a magnet’s magnetic north pole is near another magnet’s magnetic south pole, the magnets attract each other. This attraction causes the magnets to come together. In other words, similar poles repel, opposite poles attract.
Reading Essentials
Reading Check
3. Name What do all magnets have in common?
Key Concept Check
4. Explain What causes the forces applied by magnets?
Electricity and Magnetism
257
Earth as a Magnet How does a magnetic compass help you find Earth’s geographic North Pole? A compass needle is a small bar magnet. Like all magnets, a magnetic field surrounds a compass needle.
Reading Check
5. State Which of Earth’s geographic poles is about in the same location as Earth’s magnetic south pole?
Flowing molten iron and nickel in Earth’s outer core create a magnetic field around Earth. Therefore, Earth has a magnetic north pole and a magnetic south pole. Recall that the opposite poles of two magnets attract each other. Thus, the compass needle’s magnetic north pole points toward Earth’s magnetic south pole. This means that Earth’s magnetic south pole is near Earth’s geographic North Pole.
Magnets Why do magnets attract only some materials? Remember, all matter is made of atoms. A magnetic field surrounds each atom. In some materials, atoms are grouped in magnetic domains. A magnetic domain is a region in a magnetic material in which the magnetic fields of the atoms all point in the same direction. The magnetic fields of the atoms within a domain combine into a single field around the domain. Think of a magnetic domain as a tiny magnet within a material.
Nonmagnetic Materials
Magnetic
Nonmagnetic
Key Concept Check
6. Compare How are magnets and magnetic domains related?
258
Electricity and Magnetism
Magnetic Materials In some materials, such as iron and steel, atoms are grouped in magnetic domains. These materials are called magnetic materials. However, not all magnetic materials are magnets. For example, the magnetic fields of the domains of a steel nail point in different directions. The magnetic fields of these domains cancel out the magnetic effects of each other. Here, the magnetic material is not a magnet. A magnetic material becomes a magnet as the magnetic fields of the material’s magnetic domains line up to point in the same direction. The aligned magnetic fields of the domains combine to form a single magnetic field around the entire object. In this case, the magnetic material is a magnet.
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Create a horizontal two-tab book and use it to describe and to collect examples of magnetic and nonmagnetic materials.
Most materials, including aluminum and plastic, do not have atoms grouped in magnetic domains. The atoms point in many different directions. The random magnetic fields cancel out the magnetic effects of each other. These nonmagnetic materials cannot be made into magnets.
Temporary and Permanent Magnets Some magnetic materials lose their magnetic fields quickly. Other materials keep their magnetic fields for a long time. How long a magnet remains a magnet depends partly on the material from which it is made. Soft magnetic materials are not soft to the touch. They are called soft because they quickly lose their magnetic fields. Materials that keep their magnetic fields for long periods of time are hard magnetic materials.
Temporary Magnets Placing a soft magnetic material, such
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
as iron, in a strong magnetic field causes the material’s magnetic domains to line up. Temporary Magnet a) This makes the material a magnet. When the material is moved away from the magnetic field, its domains return to their random positions, and the material is no longer a magnet. In part a b) of the figure to the right, the nail is not a magnet. However, in part b, the nail is a magnet. This happens because the magnet’s magnetic field causes the magnetic field of the nail’s magnetic domains to line up. Thus, the nail becomes a magnet. The nail is a temporary magnet because it attracts other magnetic materials only if it is in the magnetic field of another magnet.
Permanent Magnets Hard magnetic materials are mixtures of iron, nickel, and cobalt combined with other elements. When a hard magnetic material is placed in an extremely strong magnetic field, the material’s magnetic domains align and lock into place.
Reading Check
7. Name the two types of magnetic materials.
Visual Check
8. Identify Circle the nail that shows magnetic domains in alignment.
Reading Check
9. Explain Why do soft magnetic materials make temporary magnets?
When a magnet made in this way is removed from the strong magnetic field, the object remains a magnet permanently, unlike a temporary magnet. Lodestone, a naturally occurring permanent magnet, is found in Earth’s crust. Other permanent magnets can be made with electric devices called magnetizers.
Reading Essentials
Electricity and Magnetism
259
Combining Electricity and Magnetism
Reading Check
10. Define What is electromagnetism?
In 1820, Danish scientist Hans Christian Ørsted noticed that a compass needle moved when a nearby electric current was switched on. He was convinced there was a relationship between electricity and magnetism. Today, we call this relationship electromagnetism. Almost all the electrical devices in your home, if they use an electric motor, depend on electromagnetism.
Magnetic fields produce electric currents. Recall that a generator is a machine that produces an electric current. As shown in the figure below, you can make a simple generator. All you need is a small wire coil connected in a circuit and a magnet. When you move the magnet through the center of the coil, the magnet’s magnetic field moves over the loops of the coil. The moving magnetic field forces an electric current to flow through the circuit. When the magnet stops moving, the current stops, too.
How a Generator Works –
Visual Check
0
+
N
S
Motion of magnet
Key Concept Check
12. Summarize How do electric currents and magnetic fields interact?
260
Electricity and Magnetism
More complex generators use wire coils with more loops and stronger magnets that rotate in place. You can produce an electric current by using a hand-cranked generator to rotate a magnet within a small wire coil. The hand-cranked generator produces only a small amount of electric current. Huge generators use coils with several kilometers of wire and giant magnets to produce the electric current that is supplied to homes, buildings, and cities.
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
11. Identify Circle the magnetic field.
Electric currents produce magnetic fields. Recall that some magnetic materials become temporary magnets when placed in the magnetic field of another magnet. There is another type of temporary magnet that is very common and useful.
N S
13. Draw Trace the flow of electric current in the wire.
S
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Visual Check
N
S N
S N
Hans Ørsted discovered that a Magnetic Field magnetic field surrounds a + current-carrying wire. The magnetic field is shown as a series of circles in the figure to the right. If a current-carrying wire is wound into a coil, the magnetic field becomes stronger. When a soft magnetic material is placed within the coil, the – magnetic field becomes even stronger. A temporary magnet made with a current-carrying wire coil wrapped around a magnetic core is an electromagnet.
Electromagnets are useful because they can be controlled in ways other magnets cannot. First, an electromagnet’s magnetic field can be turned off and on. Turning off the electric current in the coil turns off the magnetic field. Second, the north and south poles of the electromagnet reverse when the current reverses. And finally, the strength of an electromagnet can be controlled with the number of loops in the coil and the amount of electric current in the coil.
Reading Check
14. Summarize How can the strength of an electromagnet be controlled?
Reading Essentials
Electricity and Magnetism
261
Mini Glossary electromagnet: a temporary magnet made with a current-
magnetic force: a push or a pull a magnetic field applies to
carrying wire coil wrapped around a magnetic core
either a magnetic material or an electric current
magnet: an object that attracts iron and other materials that
magnetic material: any material that a magnet attracts
have magnetic qualities similar to iron
magnetic domain: a region in a magnetic material in which the magnetic fields of the atoms all point in the same direction
1. Review the terms and their definitions in the Mini Glossary. Write a sentence explaining how a magnetic material can become a magnet.
2. Use the graphic organizer to identify the two types of magnetic materials. Then state one similarity and one difference between the two types. Similarity
Difference
3. You hold two bar magnets close together; however, instead of sticking to teach other, they push apart. Explain why.
What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?
262
Electricity and Magnetism
Connect ED
Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.
END OF LESSON
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Types of magnetic materials
PERIODIC TABLE OF THE ELEMENTS 1
1
Hydrogen 1
2
H
Gas
Hydrogen 1
Element Atomic number Symbol Atomic mass
Liquid
State of matter
H
Solid
1.01
Synthetic
1.01
2
3
4
5
6
7
Lithium 3
Beryllium 4
6.94
9.01
Sodium 11
Magnesium 12
22.99
24.31
Potassium 19
Calcium 20
Scandium 21
Titanium 22
Vanadium 23
Chromium 24
Manganese 25
Iron 26
Cobalt 27
39.10
40.08
44.96
47.87
50.94
52.00
54.94
55.85
58.93
Rubidium 37
Strontium 38
Yttrium 39
Zirconium 40
Niobium 41
Mo
Tc
Ruthenium 44
Rhodium 45
85.47
87.62
88.91
91.22
92.91
95.96
(98)
101.07
102.91
Cesium 55
Barium 56
Lanthanum 57
Hafnium 72
Tantalum 73
Tungsten 74
Rhenium 75
Osmium 76
Iridium 77
132.91
137.33
138.91
178.49
180.95
183.84
186.21
190.23
192.22
Francium 87
Radium 88
Actinium 89
Rutherfordium 104
Dubnium 105
Seaborgium 106
Bohrium 107
Hassium 108
Meitnerium 109
(223)
(226)
(227)
(267)
(268)
(271)
(272)
(270)
(276)
Li
Na
K
Rb
Cs
Fr
A column in the periodic table is called a group.
Be
3
Mg
Ca
Sr
Ba
Ra
Sc
Y
La
Ac
4
Ti
Zr
Hf
Rf
5
V
Nb
Ta
Db
6
Cr
7
Mn
Molybdenum Technetium 43 42
W
Sg
Re
Bh
9
8
Fe
Ru
Os
Hs
Co
Rh
Ir
Mt
The number in parentheses is the mass number of the longest lived isotope for that element.
A row in the periodic table is called a period.
Lanthanide series
Actinide series
Cerium 58
Praseodymium Neodymium Promethium 59 60 61
Samarium 62
Europium 63
Pr
Nd
Pm
140.12
140.91
144.24
(145)
150.36
151.96
Thorium 90
Protactinium 91
Uranium 92
Neptunium 93
Plutonium 94
Americium 95
232.04
231.04
238.03
(237)
(244)
(243)
Ce
Th
Pa
U
Np
Sm
Pu
Eu
Am
Metal
18
Metalloid Nonmetal
13
Recently discovered
14
11
17
16
He
4.00 Boron 5
Carbon 6
Nitrogen 7
Oxygen 8
Fluorine 9
Neon 10
10.81
12.01
14.01
16.00
19.00
20.18
Aluminum 13
Silicon 14
Phosphorus 15
Sulfur 16
Chlorine 17
Argon 18
26.98
28.09
30.97
32.07
35.45
39.95
B
10
15
Helium 2
12
C
Al
Si
N
O
P
S
F
Ne
Cl
Ar
Nickel 28
Copper 29
Zinc 30
Gallium 31
Germanium 32
Arsenic 33
Selenium 34
Bromine 35
Krypton 36
58.69
63.55
65.38
69.72
72.64
74.92
78.96
79.90
83.80
Palladium 46
Silver 47
Cadmium 48
Indium 49
In
Tin 50
Sn
Antimony 51
Tellurium 52
Iodine 53
Xenon 54
106.42
107.87
112.41
114.82
118.71
121.76
127.60
126.90
131.29
Platinum 78
Gold 79
Mercury 80
Thallium 81
Lead 82
Bismuth 83
Polonium 84
Astatine 85
Radon 86
195.08
196.97
200.59
204.38
207.20
208.98
(209)
(210)
(222)
Ni
Pd
Pt
Cu
Ag
Au
Ga
Zn
Cd
Hg
Darmstadtium Roentgenium Copernicium 110 111 112
Ds
Rg
Cn
(281)
(280)
(285)
Ge
Pb
Tl
Ununtrium 113
*
Uut
(284)
As
Sb
Bi
Se
Te
Po
Br
Uuq
(289)
*
Uup
(288)
*
Xe
I
At
Ununquadium Ununpentium Ununhexium 114 115 116
*
Kr
Rn
Ununoctium 118
*
Uuh
Uuo
(294)
(293)
* The names and symbols for elements 113-116 and 118 are temporary. Final names will be selected when the elements’ discoveries are verified. Gadolinium 64
Terbium 65
Dysprosium 66
Holmium 67
Erbium 68
Thulium 69
Ytterbium 70
Lutetium 71
157.25
158.93
162.50
164.93
167.26
168.93
173.05
174.97
Curium 96
Berkelium 97
Californium 98
Einsteinium 99
Fermium 100
Mendelevium 101
Nobelium 102
Lawrencium 103
(247)
(247)
(251)
(252)
(257)
(258)
(259)
(262)
Gd
Cm
Tb
Bk
Dy
Cf
Ho
Es
Er
Fm
Tm
Md
Yb
No
Lu
Lr
