Download Blizzard Bag 2

Mr. Smith Physical Science Blizzard Bag Number Two.
Accompanying notes and lesson plan included.
Academic/Career & Technical Related/Demonstration Lesson Plan
Title: “Blizzard Bag Number Two – Physical Science”
Scope/Sequence: First of Three covering chapter 10 Electromagnetic Induction
State Indicator/Competency:
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Electricity and Magnetism
Magnetic fields and energy
Electromagnetic fields and energy
Instructional Objective(s):
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At the end of this lesson, the student will be able to state the definition of a magnetic domain with 100
percent accuracy
At the end of this lesson, the student will be able to name the ways to create and destroy permanent
magnets with 100 percent accuracy
At the end of this lesson, the student will be able to name the parts of an electromagnet with 100
percent accuracy
At the end of this lesson, the student will be able to state the two factors that can increase the magnetic
field of an electromagnet with 100 percent accuracy
At the end of this lesson, the student will be able to state the effect of a magnetic field on a stationary
charged particle with 100 percent accuracy
At the end of this lesson, the student will be able to state the effect of a magnetic field on a moving
charged particle with 100 percent accuracy
At the end of this lesson, the student will be able to state the direction of the deflecting force on a
charged particle in a stationary magnetic field with 100 percent accuracy
At the end of this lesson, the student will be able to list the parts of a galvanometer with 100 percent
accuracy
At the end of this lesson, the student will be able to state the name of a galvanometer when it is used to
measure current with 100 percent accuracy
At the end of this lesson, the student will be able to state the name of a galvanometer when it is used to
measure potential with 100 percent 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.
Name:__________________________
Points:___/10
Physical Science Blizzard Bag Number Two
Chapter 10 Magnetism
Lesson 3 - Magnetic Domains, Electromagnets
Lesson 4 – Magnetic Fields and Moving Charges
Date Due:
Lesson Objectives
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state the definition of a magnetic domain
name the ways to create and destroy permanent magnets
name the parts of an electromagnet
state the two factors that can increase the magnetic field of an electromagnet
state the effect of a magnetic field on a stationary charged particle
state the effect of a magnetic field on a moving charged particle
state the direction of the deflecting force on a charged particle in a stationary magnetic field
list the parts of a galvanometer
state the name of a galvanometer when it is used to measure current
state the name of a galvanometer when it is used to measure potential
Vocabulary:
tesla weber gauss Cosmic rays -
Guided Notes:
10.3 Magnetic Domains
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Making and Destroying Permanent Magnets
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Measuring Magnets
You can measure magnetic fields using instruments like gauss meters, and you can
describe and explain them using numerous equations. Here are some of the basics:
• Magnetic lines of force, or flux, are measured in Webers (Wb). In electromagnetic
systems, the flux relates to the current.
• A field's strength, or the density of the flux, is measured in Tesla (T) or gauss (G).
One Tesla is equal to 10,000 gauss. You can also measure the field strength in
Webers per square meter. In equations, the symbol B represents field strength.
• The field's magnitude is measured in amperes per meter or oersted. The symbol H
represents it in equations.
Electric Currents and Magnetic Fields
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Electromagnets
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Magnetic Forces on Moving Charges
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Magnetic Force on Current Carrying Wires
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Electric Meters
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Associated Text:
10.3 Magnetic Domains
The magnetic field of an individual atom is so strong that interactions among adjacent atoms cause large
clusters of them to line up with one another. These clusters of aligned atoms are called magnetic
domains. Each domain is made up of billions of aligned atoms. The domains are microscopic (Figure
10.7), and there are many of them in a crystal of iron. Like the alignment of iron atoms within domains,
domains themselves can align with one another.
Not every piece of iron is a magnet because the domains in ordinary iron are not aligned. In a
common iron nail, for example, the domains are randomly oriented. But when you bring a magnet
nearby, they can be induced into alignment. (It is interesting to listen, with an amplified stethoscope, to
the clickety-clack of the domains aligning in a piece of iron when a strong magnet approaches.) The
domains align themselves much as electrical charge in a piece of paper align themselves (become
polarized) in the presence of a charged rod. When you remove the nail from the magnet, ordinary
thermal motion caused most or all of the domains in the nail to return to a random arrangement.
Permanent magnets can be made by placing pieces of iron or similar magnetic materials in a strong
magnetic field. Alloys of iron differ; soft iron is easier to magnetize than steel. It helps to tap the
material to nudge any stubborn domains into alignment. Another way is to stroke the material with a
magnet. The stroking motion aligns the domains. If a permanent magnet is dropped or heated outside
of the strong magnetic field from which it was made, some of the domains are jostled out of alignment
and the magnet becomes weaker.
10.4 Electric Currents and Magnetic Fields
A moving charge produces a magnetic field. A current of charges, then also produces a magnetic field.
The magnetic field that surrounds a current-carrying wire can be demonstrated by arranging an
assortment of compasses around the wire (Figure 10.10). The magnetic field about the current-carrying
wire makes a pattern of concentric circles. When the current reverses direction, the compass needles
turn around, showing that the direction of the magnetic field changes also.
If the wire is bent into a loop, the magnetic field lines become bunched up inside the loop (Figure
10.11). If the wire is bent into another loop that overlaps the first, the concentration of magnetic field
lines inside the loops are doubled. It follows that the magnetic field intensity in this region is increased
as the number of loops is increased. The magnetic field intensity is appreciable for a current-carrying
wire that has many loops.
Electromagnets
If a piece of iron is placed in a current-carrying coil of wire, the alignment of magnetic domains in the
iron produces a particularly strong magnet known as an electromagnet. The strength of an
electromagnet can be increased simply by increasing the current through the coil. Strong
electromagnets are used to control charged-particle beams in high-energy accelerators. They also
levitate and propel prototypes of high-speed trains. (Figure 10-14).
10.5 Magnetic Forces on Moving Charges
A charged particle at rest will not interact with a static magnetic field. However, if the charged particle
moves in a magnetic field, the magnetic character of a charge in motion becomes evident: The charged
particle experiences a deflecting force. The force is greatest when the particle moves in a direction
perpendicular to the magnetic field lines. At other angles, the force is less, and it becomes zero when
the particle moves parallel to the file lines. In any case, the direction of the force is always
perpendicular to the magnetic field lines and the velocity of the charged particle (Figure 10-15). So a
moving charge is deflected when it crosses through a magnetic field, but, when it ravels parallel to the
field, no deflection occurs.
The deflecting force is very different from the forces that occur in other interaction, such as the
gravitation forces between masses, the electric forces between charges, and the magnetic forces
between magnetic poles. The force that acts on a moving charged particle, such as an electron in an
electron beam, does not act along the line that joins the source of interaction. Instead, it acts
perpendicularly both to the magnetic field and to the electron beam.
We are fortunate that charged particles are deflected by magnetic fields. This fact is employed in
guiding electrons onto the inner surface of a television picture tube to produce a picture. Also, charged
particles from outer space are deflected by the earth’s magnetic field. Otherwise the harmful cosmic
rays bombarding the earth’s surface would be much more intense.
Magnetic Force on Current Carrying Wires
Simple logic tells you that if a charged particle moving through a magnetic field experiences a deflecting
force, then a current of charged particles moving through a magnetic field also experiences a deflecting
force. If the particles are deflected while moving inside a wire, the wire is also deflected (Figure 10-17).
If we reverse the direction of current, the deflecting force acts in the opposite direction. The force is
strongest when the current is perpendicular to the magnetic field lines. The direction of force is not
along the magnetic field lines nor along the direction of current. The force is perpendicular to both the
field lines and current. It is a sideways force.
We see that, just as a current-carrying wire will deflect a magnet such as a compass needle (as
discovered by Oersted in a physics classroom in 1820), a magnet will deflect a current-carrying wire.
When discovered, these complementary links between electricity and magnetism created much
excitement. Almost immediately, people began harnessing the electromagnetic force for useful
purposes – with great sensitivity in electric meters and with great force in electric motors.
Electric Meters
The simplest meter to detect current is a magnetic compass. The next simplest meter is a compass in a
coil of wires (Figure 10.18). When an electric current passes through the coil, each loop produces its
own effect on the needle, so even a very small current can be detected. Such a current-indicating
instrument is called a galvanometer.
A more common design is shown in Figure 10.19. It employs more loops of wire and it is therefore
more sensitive. The coil is mounted for movement, and the magnet is held steady. The coil turns
against a spring, so the greater the current in its windings, the greater the deflection. A galvanometer
may be calibrated to measure current (amperes), in which case it is called a ammeter. Or it may be
calibrated to measure electric potential (volts), in which case it is called a voltmeter.
Electric Motors
If we change the design of a galvanometer slightly, so that the deflection makes a complete turn rather
than a partial rotation, we have an electric motor. The principle difference is that the current in a motor
is made to change direction each time the coil makes half a rotation. This happens in a cyclic fashion to
produce continuous rotation, which has been used to run clocks, operate gadgets, and lift heavy loads.
In Figure 10.21 we see the principle of the electric motor in bare outline. A permanent magnet
produces a magnetic field in a region where a rectangular loop of wire is mounted to turn about the axis
shown by the dashed line. When a current passes through the loop, it flows in opposite directions in he
upper and lower sides of the loop. (It must do this because, if charge flows into one end of the loop, it
must flow out the other end). If the upper portion of the loop is force to the left, then the lower portion
of the loop is forced to the right, as if it were a galvanometer. But, unlike a galvanometer, the current is
reversed during each half revolution by means of stationary contacts called brushes. In this way, the
current in the loop alternates so that the forces in the upper and lower regions do not change direction
as the loop rotates. The rotation is continuous as long as current is supplied.
We have described here only a very simple DC motor. Larger motors, DC or AC, are usually
manufactured by replacing the permanent magnet by an electromagnet that is energized by the power
source. Of course, more than a single loop is used. Many loops of wire are wound about an iron
cylinder, called an armature, which then rotates when the wire carries current.
The advent of electric motors brought to an end much human and animal toil in many parts of the
world. Electric motors have greatly changed the way people live.
Guided Reading Questions:
use the chapter text and guided notes found above
10.3 Magnetic Domains
6. What is a magnetic domain?
7. Why is iron magnetic and wood not?
8. Why will dropping an iron magnet on a hard floor make it a weaker magnet?
10.4 Electric Currents and Magnetic Fields
9. What is the shape of a magnetic field about a current-carrying wire?
10. What happens to the direction of the magnetic field about an electric current when the direction of
the current is reversed?
11. Why is the magnetic field strength inside a current-carrying loop of wire greater than the field
strength about a straight section of wire?
12. How is the strength of a magnetic field in a coil affected when a piece of iron is placed inside?
10.5 Magnetic Force on Moving Charges
13. In what direction relative to a magnetic field does a charged particle move in order to experience
maximum deflecting force?
14. Both gravitational and electrical forces act along the direction of the force fields. How does the
direction of the magnetic force on moving charged particles differ?
15. What effect does the earth’s magnetic field have on the intensity of cosmic rays striking the earth’s
surface?
16. Since a magnetic force acts on a moving charged particle, does it make sense that a magnetic force
also acts on a current-carrying wire? Defend your answer.
17. What relative direction between a magnetic field and a current-carrying wire results in the greatest
force on the wire? In the smallest force?
18. What happens to the direction of the force on a wire when the current in it is reversed?
19. What is a galvanometer called when it is calibrated to read current? To read voltage?
20. Is it correct to say that an electric motor is a simple extension of the physics that underlies a
galvanometer?
Physical Science
Blizzard Bag Notes
Chapter 10 Magnetism and Electromagnetic Induction
Vocabulary
tesla - a unit of measurement of magnetic flux (the strength of a magnetic field)
weber - a measurement the density of the magnetic flux
gauss - a unit of measurement of magnetic flux (the strength of a magnetic field), 1 tesla = 10,00 gauss
Cosmic rays - high energy particles (typically protons, neutrons, electrons) that originate from celestial
objects, primarily the sun, but secondarily other stars.
Lesson Three Notes
10.3 Magnetic Domains
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Clusters of aligned atoms are called magnetic domains.
Magnetic domains contain billions of atoms.
Magnetic domains are microscopic.
Every piece of iron contains billions of magnetic domains.
Not every piece of iron is a magnet because the domains in ordinary iron are not aligned.
When you bring a magnet close to a magnetizable object, the domains are induced into alignment.
When you remove the object from the magnet, ordinary thermal motion causes most or all of the
domains to return to a random arrangement.
Making and Destroying Permanent Magnets
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Permanent magnets can be made by placing pieces of iron or similar magnetic materials in a strong
magnetic field
Nudging helps align the domains
If a permanent magnet is dropped or heated outside of the strong magnetic field from which it was made,
some of the domains are jostled out of alignment and the magnet becomes weaker.
Measuring Magnets
You can measure magnetic fields using instruments like gauss meters, and you can describe and explain
them using numerous equations. Here are some of the basics:
• Magnetic lines of force, or flux, are measured in Webers (Wb). In electromagnetic systems, the
flux relates to the current.
• A field's strength, or the density of the flux, is measured in Tesla (T) or gauss (G). One Tesla is
equal to 10,000 gauss. You can also measure the field strength in Webers per square meter. In
equations, the symbol B represents field strength.
• The field's magnitude is measured in amperes per meter or oersted. The symbol H represents it
in equations.
Electric Currents and Magnetic Fields
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A moving charge produces a magnetic field.
A current of charges also produces a magnetic field.
The magnetic field about the current-carrying wire makes a pattern of concentric circles.
When the current reverses direction the direction of the magnetic field reverses also.
Electromagnets
An electromagnet is a piece of magnetic material placed in a loop of current carrying wire.
The strength of an electromagnet can be increased by:
1) increasing the current through the coil
2) increasing the number of coils
Lesson Four Notes
Magnetic Forces on Moving Charges
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A charged particle at rest will not interact with a static magnetic field.
However, if the charged particle moves in a magnetic field, the magnetic character of a charge in motion
becomes evident:
The charged particle experiences a deflecting force.
The force is greatest when the particle moves in a direction perpendicular to the magnetic field lines.
At other angles, the force is less, and it becomes zero when the particle moves parallel to the file lines.
In any case, the direction of the force is always perpendicular to the magnetic field lines and the velocity
of the charged particle.
The deflecting force is very different from the forces that occur in other interactions.
In every other interaction the force acts along a line that joins the sources of interaction.
The force that acts on a moving charged particle acts perpendicularly both to the magnetic field and to
the electron beam.
Magnetic Force on Current Carrying Wires
If a charged particle moving through a magnetic field experiences a deflecting force, then a current of
charged particles moving through a magnetic field also experiences a deflecting force.
If the particles are deflected while moving inside a wire, the wire is also deflected
The force is perpendicular to both the field lines and current.
We harness the electromagnetic force for useful purposes – with great sensitivity in electric meters and
with great force in electric motors.
Electric Meters
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A galvanometer:
5) magnetic compass in a coil of wires
6) detects small currents
7) calibrated to measure current (amperes), it is called an ammeter
8) calibrated to measure electric potential (volts), t is called a voltmeter.