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Introduction
Magnetism
What is the mysterious force that enables some
materials to attract others?
How could pieces of rock attract and repel each
other?
Prepared By
Ghulam Hussain
Rajeev Sharma
History
As early as 600 B.C. the Greeks discovered that a certain type of
iron ore , later known as Lodestone, or Magnetite was able to
attract other small pieces of iron. Also when pivoted and allowed
to rotate freely, a piece of Lodestone would come to rest in a
North-South position. Because of this property, Lodestone was
widely used in navigation. The Lodestone is the rock that
displayed natural magnetism.
Chemical analysis has shown that Lodestone gets its magnetic
properties from the presence of an oxide of iron, Fe3O4 , Known
today as magnetic iron ore.
Compass
A compass is simply a magnet that is allowed to rotate
horizontally to point north and south.
Early compass makers shaped lodestones so that one end always
pointed towards Earth geographic north and the other towards
the geographic south. Later on these ends were named as North
and South Poles of a Compass.
The invention of the compass enabled sailors to leave the coast
and venture out into the ocean knowing they could find their
way back with the compass. This resulted in the great global
explorations of the fifteenth and sixteenth centuries, including
the discovery of the “New World”
Albert Einstein recalled that, as a child, he had been fascinated
by compass
Lab. Activity---- Making a magnet
Use a magnet to change a steel paper clip into a magnet. Use a
compass to test the results.
Materials: Steel paper clips, compass, bar magnet
• Straighten out the paper clips. Bring the compass close to the paper
clip and move it all the way around the paper clip. Note the effect
on the compass needle.
• Drag the north end of the magnet in a sweeping motion along the
paper clip several times. Make sure the sweeping motion is from
left to right and that the magnet is lifted high above the paper clip
when moving from right to left.
• Bring the compass close to the paper clip and move it all the way
around the paper clip. Note the effect on the compass needle.
Making list of observations recorded.
Domain Theory of Magnetism
In domain theory, the material is affected by the presence of a magnet if the
atoms or molecules of the material are magnets. A domain is a group of
adjacent atoms whose like poles have “like” orientations within the material.
When the domains of a material are randomly oriented, the material shows
no permanent magnetism. The presence of an external magnet can induce
the domains to become aligned , more or less with that of the external
magnet. Thus, the material becomes a magnet in its own right.
In some magnetic materials, such as iron, the microscopic domains are easily
reoriented in the direction parallel to the external applied field . How ever,
when the external magnet is removed, the domains return to their random
orientations and the magnetism disappears. The iron and such other
materials form temporary magnets. In other materials, such as steel, the
internal domains are reoriented only with considerable difficulty. When the
external magnet is removed , however random re-alignment of the domains is
also difficult. Thus the material will retain its magnetic properties. These
types of materials form permanent magnets.
Ferromagnetism
Small pieces of iron rubbed in one direction with lodestone become magnetized . Even
bringing a piece of iron near a magnet causes the iron to be magnetized. Nickel and
cobalt , and any alloy containing nickel, cobalt, or iron behave in the same way. These
substances are called ferromagnetic, and you can induce them to become magnetized by
placing them in a magnetic field.
Demagnetization
Dropping or heating an induced magnet will cause its aligned poles to return to random
directions. Some materials, such as pure iron, revert to random alignment as soon as
they are removed from the magnetizing field. Substances that can become instantly
demagnetized are called soft ferromagnetic materials. Iron can be alloyed with certain
materials, such as Aluminum and Silicon , that have keeping the dipoles aligned even
when the magnetizing field is removed. These alloys are used to make permanent
magnets and are referred to as hard ferromagnetic materials.
Breaking a Bar Magnet
Breaking a bar magnet produces two pieces of iron whose dipole alignment is identical to
the original piece. Both pieces will also be magnets, with N-poles and S-poles at opposite
ends. Continuous breaking will produce the same results, since the domains within the
magnet remain aligned even when the magnet is broken.
Earth Magnet
In 1600, William Gilbert, an English Scientist showed that the earth has the properties
of a magnet. He fashioned a lodestone into the shape of a sphere (a model of Earth) .
After using a compass to locate the poles of his lodestone sphere , he decided that,
since it attracted the North pole of a compass, the magnet pole in the Arctic region of
the Earth had to be a magnetic South-pole. The Antarctic region must contain a
magnetic North-pole. A compass needle placed on the surface of Gilbert’s lodestone
sphere behaved like a compass on the surface of Earth. He argued that Earth itself
must be a giant spherical magnet.
(Gilbert’s lodestone Sphere)
Long before Gilbert’s time, it was noticed that a compass did not point directly
towards true geographic north. In 1580, in London, it was recorded that a compass
needle pointed 11 degree east of north. This is known as Magnetic Declination.
To use a magnet compass effectively, you must be aware of the magnetic declination
at your location on Earth. Detailed maps have been prepared that provide very
accurate readings of the magnetic declination everywhere on Earth.
Law of Magnetic Poles
Opposite Magnetic Poles attract.
Similar Magnetic Poles repel.
Magnetic Field of Force
The space around a magnet in which magnetic forces are exerted.
A magnetic field is represented by a series of lines around a magnet ,showing
the path the N-pole of small test compass would take if it were to move freely
in the direction of the magnetic force. Then, at any point in the field , a
magnetic field line indicates the direction in which the N-pole of the test
compass would point.
Lab. Activity:
Magnetic Fields
To observe the magnetic force at
a given point in a magnetic field
we can use a small test compass
with clearly marked poles. To
demonstrate the magnetic field
around a magnet, iron filings are
sprinkled around the magnet.
Materials: Two bar magnets, Iron
filings, Sheet of Acetate (or paper),
Small compass.
Precautions:
Be careful not to get iron fillings in
your eyes. Wash your hands after
handling iron filings.
Instuctions:• Cover the bar magnet with the sheet of
acetate(or paper).Carefully sprinkle the iron
filings onto the sheet of acetate around the
bar magnet and look for any patterns
formed by the iron fillings, especially near
the poles of the magnet . Sketch any
patterns that you find.
• Use the compass to indicate the direction of
the field around the space above the bar
magnet. Draw a three-dimensional picture
of the magnetic field around the magnet.
• Repeat the procedure for the following
cases:(1) Like poles close to each other
(2)opposite poles close to each other
(3)magnets side by side
Electromagnetism
Hans Oerstead accidently discovered Electromagnetism. Prior to his
discovery, Scientists believed that electricity and magnetism were
separate phenomena. He proved that whenever electric current
passes through a conductor , a magnetic field is produced around that
conductor.
The discovery of Electromagnetism has revolutionized the field of
Magnetism. Now we are surrounded by magnetism. The supplies for
electronic devices such as answering machines and calculators use
magnetism to produce safe voltages. Electric motors, big cranes,
cassette tapes, computer disks, credit cards, and pass cards involve
magnetism.
A you tube video on Electromagnetic induction will also be played in
the class room.
http://www.youtube.com/watch?v=VPxdl1zpcC8&feature=youtu.be
Magnetism - a Gizmo(a Computer-Based
Simulation)
In this activity students will work in small
groups. They will have to follow the code of
conducts about the constructive use of
computers.
After this activity students will be able to
•Determine which materials are attracted to
a bar magnet.
•Define the term "ferromagnetic."
•Observe the interaction of bar magnets.
•Determine that like poles repel and opposite
poles attract.
•Understand that magnets exert force at a
distance.
•Observe magnetic field lines for attracting
and repelling magnets.
•Use magnetic field lines to predict if an
object will be attracted to a magnet or
repelled.
•Observe magnetic field lines produced by
ferromagnetic materials
At the end of the activity,
students will be handed over a
“Student Activity Sheet "to fill it
out and return to the teacher. It
will help to assess the students
performance.
In this activity students will observe the
following activities on computer:– Warm-up – Students discover which
materials are ferromagnetic.
– Activity A – Students determine when
magnets attract one another and when
they repel one another.
– Activity B – Students observe magnetic
field lines produced by lone magnets
and pairs of magnets.
– Extension – Students observe magnetic
field lines produced by a magnet and
other materials, some of which are
ferromagnetic.
All the students will work on this
Gizmo at the following web site
address:http://www.explorelearning.com/index
.cfm?method=cResource.dspDetail&
ResourceID=631
Applications of Magnetism in every day life
There are numerous applications of Electromagnetism in almost every
field of life. Lifting electromagnets, electromagnetic relay, door
chimes, electric bell, motors, transformers are few examples. Kitchen
appliances, such as blender, food processor, vacuum cleaner, washing
machine, dryer, Electric shaver. Most people are familiar with magnets
primarily as toys, or as simple objects for keeping papers attached to a metal
surface such as a refrigerator door.
The invention of Magnetic Resonance Imaging(MRI) has revolutionized the
field of Medical Science. It is a diagnostic technique that produces high
quality images of the inside of the human body. It is a very clear improvement
over X-rays and other methods of diagnosing illnesses. This life saving
technology enables to see and study soft tissues of the body without the
need for invasive exploratory surgery.
Maglev Trains can move at speeds around 500 Km/hour . These high speed
trains are already in operation in Japan, Germany and China. They rely upon
magnetic fields to lift the train off the tracks( to reduce friction) and so are
called Magnetic Levitation Trains. Magnetic fields are also used to propel the
trains forward. They run on electricity and release no pollutants.
Curriculum Expectations
Overall Expectations
• F1. Analyse the social, economic, and environmental impact of electrical
energy production and technologies related to electromagnetism, and
propose ways to improve the sustainability of electrical energy
production;
• F2. Investigate, in qualitative and quantitative terms, magnetic fields and
electric circuits, and solve related problems;
• F3. demonstrate an understanding of the properties of magnetic fields,
the principles of current and electron flow, and the operation of selected
technologies that use these properties and principles to produce and
transmit electrical energy.
Specific Expectations
• F3.1 Describe the properties of magnetic fields in permanent magnets
and electromagnets (e.g., the three-dimensional nature of fields,
continuous field lines, fields around current carrying conductors and coils)
• F1.1 Analyse the social and economic impact of technologies related to
electromagnetism
Lesson Sequence for Magnetism
Introduction and History
Lab Activity, Making a magnet
Domain Theory, ferromagnetism and other
important concepts of the topic.
Class demonstration about Magnetic Field lines
with the help of iron fillings
Electromagnetism, its origin . Applications and
uses in every day life. A you tube video on
Magnetic Induction will be watched on the
computer.
A computer simulation “ Magnetism” in the form
of a Gizmo
Review and Test
Teaching ideas and Assessment
Strategies
Teaching Ideas
• Lecture Method including
diagrams.
• Journal Entries
• Lab. demonstration
• Group work on computer
• Use of Internet
• Problem Solving in Pairs
• Jigsaw strategy to discuss
applications of magnetism in
important fields of life
• Activity Sheets/ Revision
Sheets.
• Home work
Assessment Strategies
Students will be assessed from
the activity sheets passed on
by the teacher at the end of
the class in addition to
observation and journal
entries
Self- Assessment method will also
be used
In order to meet the achievement
chart categories following
tools will be used:K/U Rubric, Inquiry Sheets,
Communication Rubric,
Applications marks sheets
Addressing common misconceptions
of students
• Some time students are confused about the poles of a
magnet and geographical poles. It can be addressed
from the idea of “ north seeking pole” and “south
seeking pole”
• In understanding the domain theory which is the basic
of magnetization. They should try to memorize and
understand the “Principals of Magnetism”
• Students do not understand the three-dimensional
nature of the magnetic field along a long, straight
conductor. Careful observations during any activities
and close attention to the construction of diagrams can
help with this.
Back ground Knowledge
• As this topic has not been studied in depth in
previous grades, the students should refresh
themselves with the following basics about the
topic for their benefit
•
•
•
•
•
•
•
•
•
•
How did it all begin?
Who discovered magnets?
Who were the scientists who helped us to understand magnets?
What is magnetite?
What are magnetic force fields?
What is the rule of magnetism?
How does a compass work?
Who first used a compass?
Digging deeper into terrestrial magnetism.
What are some uses of magnets?
Safety First
•
•
•
•
The slogan of work place “ Safety First” also applies in
the Lab. work and class demonstrations. It is also
covered under the curriculum expectations.
Be careful not to get iron fillings in your eyes. Wash
your hands after handling iron filings.
Computer use should be constructive. Searching
irrelevant sites is not allowed.
Be careful about the Paper clips and Bar magnets. Do
not try to lift the other personal items with the help of
magnets.
Lab. safety Policy is also in effect. Every one has to
follow the sections of the policy in letter and spirit.
Accommodations
Special need students and English Language Learners
will be accommodated.
Differentiated Learning will be in effect. Students who
still have trouble in understanding the concepts can
meet the teacher during break/recess or after school
and they will have chance to take individual help from
the teachers. Extra time will be given to ELL students to
complete activity and test sheets.
Group strategy will be used for problem solving. It will
help special need students. Teacher will provide help to
such students during the Gizmo lesson with reference
to use of computer.
References
• Grade 11 text books from Nelson, Addison Wesley,
Pearson, McGraw Hill.
• Ministry curriculum document grade 11 and 12
Science.
• www.science.nelson.com
• http://www.4dneuroimaging.com/htmlpages/index.html
• http://www.physics.ucla.edu/~msimon/
• http://www.explorelearning.com/index.cfm?method
=cResource.dspDetail&ResourceID=631
• http://www.youtube.com/watch?v=VPxdl1zpcC8&fe
ature=youtu.be