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Like poles repel
Unlike poles (opposites)
attract!
What is Magnetism?
Magnetism is the
force of
attraction or
repulsion of a
magnetic material
due to the
arrangement of its
atoms,
particularly its
electrons.
What is a magnetic
field?
• A magnetic field is the space
around a magnet in which a
magnetic force is exerted.
lodestone
compass
• A lodestone is a
“leading stone.”
• One end points
north.
• The Chinese
invented the
compass by
suspending a lode
stone on a string.
All magnetic
phenomena result from
forces between
electric charges in
motion.
The ends of a magnet are
where the magnetic effect is
the
strongest. These are called
“poles.” Each magnet has
2 poles – 1 north, 1 south.
Poles of a magnet
always
Come in pairs!
Poles of a magnet
N pole
S pole
• North-seeking
• It seeks geographic
north.
• South-seeking
• It seeks geographic
south.
What is a compass?
• A compass is a magnet that is free to move
• It responds to the Earth’s magnetic field
William Gilbert, an
English physician, first
proposed in 1600 that the
earth itself is a magnet,
and he predicted that the
Earth would be found to
have magnetic poles.
The Earth is a magnet:
North geographic pole
It exerts magnetic South magnetic pole
forces and is
surrounded by a
magnetic field
that is strongest
near the
North and South
magnetic poles
Magnetic poles
of the earth
Magnetic
South Pole
The south pole of the
earth’s magnetic field
is located close to the
north geographic
pole. The N pole of a
compass needle is
attracted to the earth’s
south magnetic pole.
Magnetic
North Pole
What is
magnetic
declination?
Magnetic
declination is the
difference between
magnetic and
geographic poles.
It measures the
angle between
them.
Demo – Which objects are
magnetic?
• We are going to try out several different
objects to see if they are magnetic or not.
• Fill in the table in your note-taking guide
with the answers.
• We will not be testing a razor blade or zinc.
What are ferromagnetic
elements?
• Materials that are strongly attracted to
magnets
• Can become temporarily magnetized
• The most common are Fe (iron),
Co (cobalt), and Ni (nickel).
Why aren’t all nails
magnetic?
Nails are only magnetic if their
domains are aligned properly.
What are domains?
• Domains are large groups of ferromagnetic
atoms whose magnetic fields are aligned
(lined up in the same direction).
• The domains are randomly oriented in
unmagnetized substances.
• The domains align themselves with an
external magnetic field (magnetic
induction).
Atoms themselves have magnetic properties due
to the spin of the atom’s electrons.
Groups of atoms join so that their magnetic fields
are all going in the same direction
These areas of atoms are called “domains”
When an unmagnetized substance is placed in a magnetic
field, the substance can become magnetized.
This happens when the spinning electrons line up in the
same direction.
An unmagnetized substance
looks like this…
While a magnetized substance
Looks like this…
Iron
Lodestone
(Magnetite)
Hard ferromagnetic materials
(alloys) make better permanent
magnets than soft iron because
their domains are harder to turn.
•
How to break a magnet:
1. Drop it
2. Heat it
This causes the domains to
become random again!
If you break a magnet in half,
S
N
S
you get 2 magnets!
N S
N
No Monopoles Allowed
It has not been shown to be possible to end up with a single
North pole or a single South pole, which is a monopole ("mono"
means one or single, thus one pole).
S
N
Note: Some theorists believe that magnetic monopoles may
have been made in the early Universe. So far, none have been
detected.
1. Breaking a magnet in two
a. destroys its magnetic properties
b. makes two smaller magnets
2. Which of these actions will NOT
demagnetize a magnet?
a. dropping it
b. heating it
c. breaking it in half
d. none of these
Magnetic Fields
The region where the magnetic forces
act is called the “magnetic field”
Direction of magnetic field lines
- Magnetic field lines
always start at north
pole and head
towards south pole.
- Magnetic field lines
are defined as the
direction the north
pole of a compass
points in a magnetic
field.
Field Lines Around a Bar Magnet
Field Lines Around a Magnetic Sphere
Field Lines of Repelling Bars
Field Lines of Attracting Bars
Field lines for horseshoe magnet
What is the advantage of using a
horseshoe magnet?
• The poles are closer together on a horseshoe
magnet, so both poles can be used at the
same time to pick up the same object.
• It doubles the pickup power.
Mapping a magnetic field
https://www.youtube.com/watch?v=fghLhJe1JLY
Vocabulary
• Magnet: material that can both attract and
repel other magnets. Iron is most common.
• Pole: Part of the magnet where the force is
S
N
the strongest
• Metal: material that is often attracted to
magnets and a good electrical conductor
• Horseshoe magnet:
• U-shaped magnet
We use the Earth’s magnetic field
to find direction.
The needle of a compass always points
toward the magnetic south pole.
We call this direction “North”
(remember, opposites attract)
Vocabulary

Geographic North pole: the north end of the
axis around which the Earth rotates

Magnetic South pole: the point on the Earth
to which a compass needle points (north end
of compass attracted to magnetic south).
Sometimes,
the Earth’s
magnetic
poles flip.
This happens
every halfmillion years
or so.
Notes on the earth’s magnetic
field.
Aurora Borealis – Northern Lights
High temperatures on the sun’s surface produce plasma,
the fourth phase of matter consisting of charged
particles. These charged particles travel throughout the
solar system as solar wind. When charged particles
reach the region of the earth’s outer atmosphere called
the magnetosphere, their motion is controlled by the
earth’s magnetic field. The charged particles are able to
slip through the earth’s magnetic field at the poles and
enter the atmosphere. They collide with electrons in
atoms of gases like oxygen and nitrogen and transfer
energy, making the electrons jump to higher energy
levels. When they fall, they give off visible light of
different colors.
The sun has a magnetic field, too.
It extends far above the sun’s
surface.
Other planets in the solar
system also have these
magnetic fields
The Earth’s magnetic field extends far into
space. It is called the “magnetosphere.”
When the magnetic particles from the sun, called “solar
wind”, strike this magnetosphere, we see a phenomenon
called…
The Aurora Borealis in the Northern Hemisphere
And the Aurora Australis in the Southern Hemisphere
1. Magnetic field lines are drawn
a. from north to south
b. from south to north
c. from positive to negative
d. from negative to positive
2. This diagram represents the magnetic
field between
a. two N poles
b. two S poles
c. N pole (left) and S pole (right)
c. S pole (left) and N pole (right)
3. The Aurora Borealis
a. originates on the sun as solar wind
b. is caused by charged particles transferring
energy to the atoms of gases in the atmosphere
c. both of these
Electromagnetism
(Add this to your notes. It is on the test)
The interaction between electric charges and
magnets is called electromagnetism
Top Five List
What We Will Learn About Magnetism
1. There are North Poles and South Poles.
2. Like poles repel, unlike poles attract.
3. Magnetic forces attract only magnetic materials.
4. Magnetic forces act at a distance.
5. While magnetized, temporary magnets act like permanent
magnets.
The end.
Go to your lab station.
Take your lab report page and something to
write with.
You will be rotating from station to station.
There are two stations for #1 because it will
take the longest to do.
If you have time, you will also visit the “making
a magnet” station.
Return to your desk afterward with your lab. It
will be turned in at the end of class.
Lab – making a temporary
magnet
• If there is time, visit this station last.
• You do not need paper or pencil.
• You should have paperclips and magnets at
each station.
• Watch the video that is on the next slide to
find out what to do.
https://www.youtube.com/watch?v=UR5Gsj-xsWE