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Mr. Smith Physical Science Blizzard Bag Number One.
Accompanying notes and lesson plan included.
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Physical Science Blizzard Bag Number One
Chapter 10 Magnetism
Lesson 1 – History and Introduction
Lesson 2 – Magnetic Fields
Lesson Objectives
• state the origin of the word magnetism
• list the historic contributions of the following scientists to the study of magnetism:
• William Gilbert
• John Mitchell
• Hans Christian Oersted
• Andre-Marie Ampere
• describe a magnetic pole
• define the force exerted by a magnetic with respect to distance of separation
• state the definition of a magnetic field
• state the direction of the magnetic field
• correlate the density of field lines with field strength
• state the fields around a stationary electric charge
• state the fields around a moving electric charge
• state the two types of electron motion within an atom
• state how the canceling of atomic electron movement makes most substances not magnetic
• state the main atomic electron motion that contributes to the magnetic field of a common
magnet
• state the main atomic electron motion that contributes to the magnetic field of a rare-earth
magnet
Vocabulary:
Magnetic field –
Magnetite –
Gauss -
Guided Notes:
Magnetism and Electromagnetic Induction
History
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Magnetic Poles
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10.2 Magnetic Fields
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Associated Text:
Magnetism and Electromagnetic Induction
The tem magnetism comes from the region of Magnesia, a province of Greece, where certain stones
were found by the Greeks more than 2000 years ago. These stones, called lodestones, had the
unusually property of attracting pieces of iron. Magnets were first fashioned into compasses and used
for navigation by the Chinese in the twelfth century.
In the sixteenth century, William Gilbert, Queen Elizabeth’s physician, made artificial magnets by
rubbing pieces of iron against lodestone, and suggested that a compass always points north and south
because the Earth has magnetic properties. Later, in 1750, John Mitchell in England found that
magnetic poles obey the inverse-square law, and his results were confirmed by Charles Coulomb. The
subjects of magnetism and electricity developed almost independently of each other until 1820, when a
Danish physicist named Hans Christian Oersted discovered in a classroom demonstration that an electric
current affects a magnetic compass. He saw that magnetism was related to electricity. Shortly
thereafter, the French physicist Andre-Marie Ampere proposed that electric currents are the source of
all magnetic phenomena.
10.1 Magnetic Poles
Anyone who has played around with magnets knows they exert forces on one another. Magnetic forces
are similar to electric forces, for they can both attract and repel without touching, depending on which
ends of the two magnets are held near one another. And similar to what we find with electric forces,
the strength of the magnetic interaction depends on the distance between the two magnets. Whereas
electric charges produce electric forces, regions called magnetic poles give rise to magnetic forces.
Suspend a bar magnet at its center by a piece of string and you’ve got a compass. One end, called the
north-seeking pole, points northward, and the opposite end, called the south-seeking pole, points
southward. More simply, these are called the north and south poles. In a simple bar magnet these poles
are located at the two ends. A common horseshoe magnet is simply a bar magnet bent into a U shape.
Its poles are also at its two ends.
When the north pole of one magnet is brought near the north pole of another magnet, they repel
each other. The same is true of a south pole near a south pole. If opposites poles are brought together,
however, attraction occurs. We find that
Like poles repel each other; opposite poles attract.
This rule is similar to the rule for the forces between electric charges, where like charges repel
one another and unlike charges attract. But there is a very important difference between magnetic
poles and electric charges. Whereas electric charges can be isolated, magnetic poles cannot. Electrons
and protons are entities by themselves. A cluster of electrons need not be accompanied by a cluster of
protons, and vice versa. The north and south poles of a magnet are like the head and tail of the same
coin.
If you break a bar magnet in half, each half still behaves as a complete magnet. Break the pieces in
half again, and you have four complete magnets. You can continue breaking the pieces in have and
never isolate a single pole. Even when your piece is one atom thick, there are two poles. This suggests
that atoms themselves are magnets.
10.2 Magnetic Fields
Sprinkle some iron filings on a sheet of paper placed on a magnet and you’ll see that the filings trace out
an orderly pattern of lines that surround the magnet. The space around the magnet contains a
magnetic field. The shape of the field is revealed by the filings, which align with the magnetic field lines
that spread out from one pole and return to the other pole. It is interesting to compare the field
patterns in Figures 10.3 and 10.5 with the electric-field patterns in Figures 9.9 and 9.10 in the previous
chapter.
The direction of the field outside a magnet is from north to the south pole. Where the lines are
closer together, the field is stronger. The concentration of iron filings at the poles of the magnet in the
following figure shows that the magnetic field strength is greater there. If we place another magnet or
small compass anywhere in the field, its poles line up with the magnetic field.
Magnetism is very much related to electricity. Just as an electric charge is surrounded by an electric
field, the same charge is also surrounded by a magnetic field if it is moving. This magnetic field is due to
the “distortions” in the electric field caused by motion and was explained by Albert Einstein in 1905 in
his special theory of relativity. We won’t go into the details except to acknowledge that a magnetic field
is a relativistic byproduct of the electric field. Charged particles in motion have associated with them
both an electric and a magnetic field. A magnetic field is produced by the motion of electric charge.
If the motion of electric charges produces magnetism, where is this motion in a common bar magnet?
The answer is, in the electrons of the atoms that make up the magnet. These electron are in constant
motion. Two kinds of electron motion contribute to magnetism: electron spin and electron revolution.
Electrons spin about their own axes like tops, and they revolve about the atomic nucleus. In most
common magnets, electron spin is the chief contributor to magnetism.
Every spinning electron is a tiny magnet. A pair of electrons spinning in the same direction makes up
a stronger magnet. A pair of electrons spinning in opposite directions, however, work against each
other. The magnetic fields cancel. This is why most substances are not magnets. In most atoms the
various fields cancel one another because the electrons spin in opposite directions. IN materials such as
iron, nickel, and cobalt, however, the fields do not cancel each other entirely. Each iron atom has four
electrons whose spin magnetism is uncanceled. Each iron atom, then, is a tiny magnet. The same is true
to a lesser extent for the atoms of nickel and cobalt. Most common magnets are therefore made from
alloys containing iron, nickel, and cobalt in various proportions.
Most common magnets are made from alloys containing iron, nickel, cobalt, and aluminum in various
proportions. In these, the electron spin contributes virtually all of the magnetic property. In the rareearth metals, such as gadolinium or neodymium, the orbital motion is more significant.
Most iron objects around you are magnetized to some degree. A filing cabinet, a refrigerator, or even
cans of food on your pantry shelf have north and south poles induced by the Earth’s magnetic field. Pass
a compass from their bottoms to their tops and their poles are easily identified. Turn cans upside down
and see how many days it takes for the poles to reverse themselves.
Guided Reading Questions:
use the chapter text and guided notes found above
1. By whom, and in what setting, was the relationship between electricity and magnetism discovered?
10.1 Magnetic Poles
2. In what way is the rule for the interaction between magnetic poles similar to the rule for the
interaction between electric charges?
3. In what way are magnetic poles very different from electric charges?
10.2 Magnetic Fields
4. What produces a magnetic field?
5. What two kinds of motion are exhibited by electrons in an atom?
Academic/Career & Technical Related/Demonstration Lesson Plan
Title: “Blizzard Bag Number One – Physical Science ”
Scope/Sequence: First of Three covering chapter 10 Electromagnetic Induction
State Indicator/Competency:
• Electricity and Magnetism
• Charging objects (friction, contact, and induction)
• Coulomb’s law
• Electric fields and electric potential energy
• DC circuits
o Ohm’s Law
o Series circuits
o Parallel circuits
o Mixed circuits
o Applying conservation of charge and energy (junction and loop rules)
• Magnetic fields and energy
• Electromagnetic fields and energy
Instructional Objective(s):
• At the end of this lesson the student will be able to state the origin of the word magnetism with 100% accuracy
• At the end of this lesson the student will be able to list the historic contributions of William Gilbert to the study of
magnetism with 100% accuracy
• At the end of this lesson the student will be able to list the historic contributions of John Mitchell to the study of
magnetism with 100% accuracy
• At the end of this lesson the student will be able to list the historic contributions of Hans Christian Oersted to the
study of magnetism with 100% accuracy
• At the end of this lesson the student will be able to list the historic contributions of Andre-Marie Ampere to the
study of magnetism with 100% accuracy
• At the end of this lesson the student will be able to describe a magnetic pole with 100% accuracy
• At the end of this lesson the student will be able to define the force exerted by a magnetic with respect to
distance of separation with 100% accuracy
• At the end of this lesson the student will be able to define a magnetic field with 100% accuracy
• At the end of this lesson the student will be able to relate magnetism to electricity with 100% accuracy
• At the end of this lesson the student will be able to state the fields generated by a static electric charge with 100%
accuracy
• At the end of this lesson the student will be able to state the fields generated by a moving electric charge with
100% accuracy
• At the end of this lesson the student will be able to Define the movement of an electron in an atom with 100%
accuracy
• At the end of this lesson the student will be able to list the component of electron motion that is prevalent in
common magnets with 100% accuracy
• At the end of this lesson the student will be able to list the component of electron motion that is prevalent in rareearth magnets with 100% accuracy
Materials:
Blizzard Bag One Handout
Vocabulary and Notes Handout
Method of Instruction:
Homework
Activities:
Students will complete worksheet at home including vocabulary, guided notes, and guided reading.
Assessment:
This assignment is worth 10 pts.
Physical Science
Blizzard Bag Notes
Chapter 10 Lesson 1 and Lesson 2
Vocabulary:
Magnetite – a naturally occurring mineral that has magnetic properties, also called lodestone
Gauss - the cgs unit of magnetic field
Magnetic field – the space around a magnet that can exert a force on another magnet or magnetic
material
Lesson One Notes
Magnetism and Electromagnetic Induction
History
- term comes from the region of Magnesia, a province of Greece
- originally called lodestones
- attracted iron
- Chinese (12th century) were the first to use magnets as compasses
- William Gilbert (16th century)
- made artificial magnets
- suggested that a compass always points north and south because the Earth has magnetic
properties
- John Mitchell (1750, England)
- found that magnetic poles obey the inverse-square law
- Hans Christian Oersted (1820)
- electric currents affected magnets
- Andre-Marie Ampere (French, 1820’s)
- electric currents are the source of magnetism
10.1 Magnetic Poles
- magnets exert forces on one another
- magnetic forces are similar to electric forces:
- they both attract and repel
- strength of force between them is inversely proportional to the square of the distance between
the two magnets
Fmagnetic ≈
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- the poles of a magnet are called north and south
- derived from Earth’s magnetic poles
- Like poles repel each other; opposite poles attract
- the poles of a magnet cannot be separated
- atoms themselves are magnets
10.2 Magnetic Fields
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The space around the magnet contains a magnetic field.
The direction of the field outside a magnet is from north to the south pole.
Where the lines are closer together, the field is stronger.
If we place another magnet or small compass anywhere in the field, its poles line up with the magnetic field.
Magnetism is very much related to electricity.
A stationary electric charge is surrounded by an electric field.
A moving electric charge is surrounded by a magnetic field.
This magnetic field is due to the relativistic “distortions” in the electric field.
Since the motion of electric charges produces magnetism, it is the motion of the electrons in the atoms of a
magnet that produce magnetism.
• These electrons are in constant motion.
• Two kinds of electron motion contribute to magnetism:
3. electron spin
4. electron revolution
• Electrons spin about their own axes like tops, and they revolve about the atomic nucleus.
• In most common magnets, electron spin is the chief contributor to magnetism.
• Every spinning electron is a tiny magnet.
• A pair of electrons spinning in the same direction makes up a stronger magnet.
• A pair of electrons spinning in opposite directions, however, work against each other.
• The magnetic fields cancel.
• This is why most substances are not magnets.
• In materials such as iron, nickel, and cobalt, however, the fields do not cancel each other entirely.
• Most common magnets are therefore made from alloys containing iron, nickel, and cobalt in various
proportions.
• In common magnets the electron spin contributes virtually all of the magnetic property.
• In the rare-earth metals, such as neodymium, the orbital motion is more significant.
• Most iron objects around you are magnetized to some degree due to the magnetic field of the Earth.
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