Download A magnet - Warren County Schools

WOW !
Magnet Magic
Magnets come in all shapes and
sizes.
round
flat
bar
horseshoe
rod
1/9 – Aurora Borelis
1/12 – compass
1/14 – magnetic field
1/15 – Electromagnet
1/16 – permanent
magnet.
1/9 – explain how the
Earth’s magnetic field
protects us.
1/12 – Explain how the
earth’s magnetic field
protects us.
1/14 – Draw a magnetic
field around a
magnet.
1/15 – Describe how
you might create an
electromagnet.
1/16 – Describe how to
decrease the force of
an electromagnet.
Explain how animals use the Earth’s
magnetic field.
 Explain why a compass points North.
 Describe how to create an electromagnetic.
 Explain how to increase or decrease the
strength of a magnet.
 Explain what made the nail a magnet.
 Explain how to create a magnet.
 Name the type of material magnets are made.

4
Name the 3 types of magnets.
 Draw a magnetic field.
 Describe what creates the Earth’s magnetic
field.
 Describe how the Earth’s magnetic field
protects the Earth.
 Contrast permanent magnets and
electromagnets.
 Describe what creates the Aurora Borelais.
 Explain how to create a compass.
 Explain why a compass always points North.

5
Magnets have been known for centuries.
The Chinese and Greeks knew about the
“magical” properties of magnets. The ancient
Greeks used a stone substance called
“magnetite.” It was discovered near Magnesta so
called it magnetite.They discovered that the stone
always pointed in the same direction. Later,
stones of magnetite called “lodestones” were
used in navigation.
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.
Magnet

Any material that attracts iron or materials
containing iron caused by alignment of
electrons.
9
Magnetic Attraction

Magnets attract metals such as iron,
nickel, and cobalt
3 Properties of Magnets
1.
2.
3.
2 poles
Exert forces
Surrounded by magnetic field
11
A magnet – strongest part is at
the poles!!!
has a
north pole
and a
south pole.
S
N
12
What Increases Strengthen of Magnet?
The strength of the force
between magnets
depends on the distance
between them.
 The magnetic force
decreases with distance
much faster than does
either gravity or the
electric force.

What Creates Magnetic
Material?
14
What Makes Materials
Magnetic?
Moving electrons produce magnetic fields
that gives an atom a north or south pole.
 In certain materials, the atoms line up to
create magnetic fields which create
domains.
 You can create a magnet by rubbing an
iron nail with a magnet.

15
Magnetic Properties of Materials

Magnetic domains in a ferromagnetic material will
always orient themselves to attract a permanent
magnet.


If a north pole approaches, domains grow that have south poles
facing out.
If a south pole approaches, domains grow that have north poles
facing out.
Properties of Magnets
Key Question:
How do magnets
interact with each
other?
The north pole attracts the
south pole of the other magnet.
S
N
S
S
N S
N
N
19
The north pole repels the north
pole of the other magnet.
S


N
N
S
You can feel the magnets pushing apart.
This is called repulsion
Note - south poles also repel each other
20
Like repels like…
Opposites attract!
Magnetic Fields
The field around a magnet where the
magnetic forces can act.
 Lines can be drawn to show the magnetic
field around a magnet.

22
Magnetic Fields
The region where the magnetic forces
act is called the “magnetic field”
The magnetic field

The number of field lines in a
certain area indicates the relative
strength of the magnetic field in
that area.

The arrows on the field lines
indicate the direction of the force.

The closer the lines are together,
the stronger the field.

Magnetic field lines always point
away from a magnet’s north pole
and toward its south pole.
The magnetic field
 All
magnets
create a
magnetic field in
the space around
them, and the
magnetic field
creates forces on
other magnets.
3 Properties of All Magnetic
Fields
1. Similar poles of two magnets always repel each
other
2. Dissimilar poles of magnets always attract each
other
3. The two poles of a magnet are indivisible. The
broken magnets act as independent magnets
and possess two poles each. It concludes that,
magnets are always bipolar.
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.
If you cut a magnet in half,
you get 2 magnets!
3 Types of Magnets
1.
2.
3.
Permanent: Difficult to magnetize but
keep the magnetism
Temporary: easy to create a magnetic
field but lose it quickly
Electromagnetic: magnet created with an
electric current.
How To Make A Magnet?

Rub a magnet on a pin!
The Earth is a magnet:
It exerts magnetic forces and is
surrounded by a
magnetic field that is strongest
near the
North and South
magnetic poles
Magnetic South Pole
Magnetic North Pole
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 Magnetic Field of the Earth
As early as 500 B.C.
people discovered that
some naturally occurring
materials— such as
lodestone and magnetite—
have magnetic properties.
 By 1200, explorers from
Italy were using a compass
to guide ocean voyages
beyond the sight of land.

NORTH POLE
The
Earth
is a
magnet
WHY??
34
The Earth is made of four layers
The Crust:
A Thin Rock Material
The Crust:
A Thin Rock Material
The Mantle:
Dense rock
The Crust:
A Thin Rock Material
The Mantle:
A Dense and Mostly Solid
Rock Material
The Outer Core:
Liquid Iron and
Nickel
The Crust:
A Thin Rock Material
The Mantle:
A Dense and Mostly Solid
Rock Material
The Outer Core:
Liquid Iron and Nickel
The Inner Core:
Solid Iron and Nickel
The Iron Core of the Earth is an
Electromagnet
The Iron Core of the Earth is an
electromagnet
The core is surrounded by
liquid Iron and Nickel
The Iron Core of the Earth is an
electromagnet
The core is surrounded by
liquid Iron and Nickel
As electrons flow around
the core the magnetic field
is produced
The Iron Core of the Earth is an
electromagnet
The core is surrounded by
liquid Iron and Nickel
As electrons flow around
the core the magnetic field
is produced
The Earth’s rotation
makes the electrons flow
at very high speeds
A little more info…
The earth’s magnetic field isn’t strong
enough for us to feel, but many animals
can sense it and even use it to navigate.
It’s only about 0.4 Gauss, much weaker
than a small magnet you can hold in your
hand.
 On average, the North & South poles “flip”
every 390,000 years. There have been 9
flips in the past 3.5 million years.

Sometimes, the
Earth’s magnetic
poles flip. This
happens every halfmillion years or so.
Magnetic North Pole
Magnetic South Pole
The poles “flip” ?
No one knows how long the process
takes, maybe a few years, maybe a few
minutes.
 Every so often, what was the North
magnetic pole suddenly becomes the
South magnetic pole.
 Lava that cools quickly on the sea floor
records these flips and lets us date them.

Why do we care?

Earth’s magnetic field isn’t just “there”
with no purpose. Without it, you and I and
every living thing on this planet would be
dead (including the cockroaches!)
The magnetic field channels away the
solar wind.
 It also prevents erosion of the atmosphere.

Solar
Wind
 So what is the solar wind anyway?
 It’s
radiation: extremely hot, high-energy,
fast-moving charged particles (ions) given off
by the sun. Most of these particles are
protons.
 If
you were exposed to it for just a few hours
without protection, your skin and every organ
in your body would be burned, and you’d
have a fatal dose of radiation poisoning.
How does the magnetic field
protect
us?
 The magnetic field captures the solar wind
and channels much of it into a donut of
radiation around the earth.
This donut (actually 2 layers – one inside the
other) is called the Van Allen Radiation Belt
(V.A.R.B.)
Where the magnetic field collapses inward,
creates the Northern and Southern Lights
Where does the radiation go?

Since the sun continually supplies new
solar wind, where does the solar wind go
that the earth has already captured?

The magnetic field channels some of it into
our atmosphere at the north & south poles.
Here it ionizes oxygen and nitrogen atoms,
causing the beautiful northern and
southern lights.
The solar wind is constantly
bombarding the Earth’s magnetic field.
Sometimes these charged particles
penetrate that field. These particles
are found in two large regions known
as the Van Allen Belts.
Where does the rest of the
radiation go?
Much of it flows through the magnetic field,
around the earth, and “drips” off the tail of
the magnetic field. The tail is called the
“magnetotail.”
 Without our “Teflon-coating” of magnetic
field, the earth would have been cooked
many billions of years ago.

Northern Lights?
The northern lights are properly called the
“aurora borealis.” They’re nothing more
than a very large fluorescent light display
(without the fluorescent tube!)
 The northern lights are sometimes seen as
far south as Florida, especially when the
sun is very active.

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…
This aurora was photographed in Tennessee in October, 2002.
The Aurora Borealis in the Northern Hemisphere
And the Aurora Australis in the Southern Hemisphere
The Magnetic Field of the Earth
Key Question:
How do we use
Earth’s magnetic
field to tell
direction?
A compass uses a tiny magnet
which can
swing round.
If opposites
attract, why does
a compass
point north?
63
The Magnetic Field of the Earth

When you use a compass, the
north-pointing end of the needle
points toward a spot near (but
not exactly at) the Earth’s
geographic north pole.

The Earth’s magnetic poles are
defined by the planet’s
magnetic field.

That means the south
magnetic pole of the planet
is near the north
geographic pole.
The North Pole of the Earth has a
“south” polarity
S
N
As a result a compass will always
point towards the North
S
N
S
N
S
N
A compass is a Magnetized
piece of metal that can spin.
S
A compass is a Magnetized
piece of metal that can spin.
N
North attracts South
S
N
The north tip of the
compass always points
towards the North Pole of
the Earth
The Magnetic Field of the Earth

Depending on where you are, a compass will point slightly
east or west of true north.
Using a compass to find
directions


A compass needle always points to the
Earth’s GEOGRAPHIC North Pole.
Really the North pole is a South
Magnetic pole
Some birds use the Earth’s magnetism
to find directions.
70