1.
MAGNETISM

2.
The Earth
Magnetic
Poles
North and
South
Geographic
Poles
North and
South
Earth is a giant magnet.

3.
MAGNETISM
Where does magnets come from?
⚫Centuries ago, it was discovered
that certain types of mineral rock
possessed unusual properties of
attraction to the metal iron. One
particular mineral, called lodestone,
or magnetite.

4.
Material is Magnetite or Iron
Oxide (Fe2 03)
Natural Magnet

5.
What is Magnetism
⚫Certain metals attract other
metals, this attraction is term
magnetism. Materials that have
magnetism is called magnets.
⚫Magnetism is produced as a
result of electrons spinning on
their own axes while rotating
about the nuclei of atoms align.
Magnetization usually results in

6.
Properties of Magnets
⚫poles of opposite effect,
denoted "north" and
"south”
⚫Scientist later found out,
that it was impossible to
isolate one of these poles
by itself by cutting a piece
of lodestone in half: each

7.
If you cut a magnet in half,
you get 2 magnets!
S N S N S N

8.
Magnetic Materials
⚫A magnetic material is one
that is attracted to a magnet
and can be made into a
magnet.
⚫One classification of
magnetic materials are:
diamagnetic, paramagnetic,
and ferromagnetic material.

9.
Diamagnetic materials
⚫Diamagnetic materials – these
materials when placed in a
magnetic field, opposes the
direction of the magnetic field.
⚫ Examples: bismuth,
antimony, copper, gold,
quartz, mercury, water,
alcohol, air, hydrogen etc.

10.
Diamagnetic materials cont’d

11.
Paramagnetic materials
⚫The paramagnetic materials
are weakly attracted by the
magnets when placed in a
magnetic field. The
paramagnetic materials feel
an attractive force towards
the strongest part of the field
when they are placed in a
non-uniform field.
Aluminum, Chromium,

12.
Ferromagnetic Material
⚫The ferromagnetic
materials have very large
values of magnetic
permeability. They have the
highest degree of
magnetization. These are
the magnetic materials,
which are found to be
attracted by magnets or

13.
Ferromagnetic Materials Cont’d
The previously un-magnetized iron becomes
magnetized as it is brought closer to the
permanent magnet. No matter what pole of the
permanent magnet is extended toward the iron

14.
ferromagnetic material cont’d
a ferromagnetic material is one that readily
and easily become magnetize.

15.
Earth’s magnetic properties
⚫Gilbert was a scientist that
showed that the Earth behaves
as a magnet
⚫The Earth’s magnetic field is
strongest at the poles
⚫Earth’s magnetic field is called
the magnetosphere

16.
Temporary magnets
⚫Easy to magnetize
⚫Lose their magnetism
quickly
⚫Ex: Soft iron

17.
Permanent magnets
⚫Hard to magnetize
⚫Stay magnetized longer
than temporary magnets
⚫Ex: alnico (cobalt,
nickel, aluminum)

18.
Types of Magnets
LOADSTON
E
BA
R
U
COIL
ALNIC

19.
Questions
⚫How is a temporary
magnet different from a
permanent magnet?
⚫Give an example of a
natural magnet.

20.
What affects magnetic
properties?
⚫Spinning electrons cause some
metals to have magnetic
properties
⚫Magnetic domains are groups
of arranged magnetic fields
⚫Dropping,hammering or
heating a magnet will cause a
magnet to lose magnetic
properties

21.
8J What’s a field?
Field is a word we all understand – it’s a
place with lots of grass!
But scientists also use the word ‘field’ with
another meaning.
A field is an area where a force acts.
So, a magnetic field is the area where a
magnet could attract something.
Can you think of any other sort of field in
science?
Magnetic Field

22.
8J What does a magnetic field look like?
Well, we can’t see it for a start, but...
Small particles of iron filings are pushed into patterns by a magnetic field. If
we sprinkle iron filings on a piece of paper over a magnet we can see...
The lines of force are very
close together here – the field
is very strong.
The lines of force are further
apart here – the field is weaker.
A line of force links one pole of a magnet to the other pole.

23.
8J And the rule about directions...
The magnetic force acts in a direction.
The arrowheads on this diagram show you the way the needle of a compass
point would go if it was free to move.
You can see that the magnetic force runs from the north pole to the south pole
of the magnet.

24.
Poles attract or repel
Laws of Magnets

25.
Can you explain what the lines of force show?
Where is the strongest part of the field?

26.
Can you explain what the lines of force show?
Where is the strongest part of the field?

27.
Testing for Magnetism
The only test for magnetism is repulsion.
If a piece of metal is attracted by a magnetic, that only proves that the
metal is made of a magnetic material. To prove that it is a magnet, it
must REPEL another magnet.
When two magnets are brought close to each other, there is a force
between them.
N S N S
N S S N
S N N S
S N S N
attra
ct
attra
ct
rep
el
rep
el

28.
Theory of Magnetism
Molecular and Electron Theories

29.
Questions
⚫Which scientist described
the Earth’s magnetic
properties?
⚫Name the devices used to
indicate geographic
direction based on the
Earth’s magnetic field.

30.
Magnetic Shielding
⚫The idea of preventing one
component from affecting
another through their common
magnetic field is called shielding.
In certain circuits stray
magnetism can cause significant
errors in measurement.
⚫Shielding materials are always
metals, because of their high
permeability; they are place over
circuit component to block any

31.
Creating Magnets
⚫The picture
shows that a
screwdriver does
not pick up
paper clips.
Methods used to create a
magnet

32.
Creating Magnets
Stroking using a permanent
magnet
■ However, after
stroking the
screwdriver
with a magnet,
the blade itself
becomes
magnetic and
attracts the
paper clips.

33.
Removing Magnetism
Heat is one way to remove
magnetism.

34.
Mike Turner, Feb. 2004
Electromagnetism
Whenever an electric current passes through a wire, a
magnetic field appears around the wire. The shape of
the field can be seen in the diagram.
Click to move on
The stronger the current is, the stronger the
magnetic field.
Some people believe that living near strong
magnetic fields, such as those produced by
power lines, can cause problems such as cancer.
Lots of scientists are working to try to find out if
this is true. At the moment, like many things in
science, the definite answer is not known.

35.
Electromagnetic Induction
⚫There is an induced emf whenever:
⚫A conductor ‘cuts’ magnetic field lines
⚫There is a relative motion between a
magnetic field and a conductor
⚫There is a change in the strength of the
magnetic field ‘linking’ a coil or circuit
⚫A coil is rotated in a magnetic field

36.
Electromagnets
To increase the strength of an electromagnet we can do three things :
Add more turns to the coil of wire
Use a bigger electric current
Wrap the coil around a soft iron core
If a steel core is used, the electromagnet will still be strong, but soon the
steel will become permanently magnetised and the electromagnet will not
be able to be switched off.
We can make an electromagnet by coiling
a wire and passing a current through it.
This is often called a solenoid.
The material that the coil is wrapped
around is called the core.

37.
Mike Turner, Feb. 2004
Using Electromagnets
Electromagnets are very useful as they can be
switched on and off, have their strength altered
or their poles switched around. They are used in
many things, especially when we want to create
movement.
Examples are :
Motors
Bells
Loudspeakers
Click to move on
The shape of the field around an electromagnet is
similar to the field around a bar magnet.

38.
The Magnetic Field of a Wire
An electromagnetic field is the magnetic field
produce by current that forms circles
around the conductor.The direction of the
field lines can be determined using the
right hand corkscrew rule. The strength of
the field can be increased by increasing the
current.
Current
Field
Lines

39.
WIRE IN A COIL
⦿To create a stronger magnetic
field force with the same
amount of electric current, we
can wrap the wire into a coil
shape, where the circling
magnetic fields around the
wire will join to create a larger
field with a definite magnetic
(north and south) polarity:

40.
Magnetic Field Direction
Cont’d
A coil of wire used to create a
magnetic field is called a solenoid.

41.
Left-Hand Rule
⦿Detailed experiments showed
that the magnetic field
produced by an electric
current is always oriented
perpendicular to the direction
of flow.
⦿A simple method of showing
this relationship is called the
left-hand rule.

42.
Magnetic Field Direction
Cont’d
⦿Simply stated, the left-hand rule
says that the magnetic flux lines
produced by a current-carrying
wire will be oriented the same
direction as the curled fingers
of a person's left hand.
⦿(in the "hitchhiking" position),
with the thumb pointing in the
direction of electron flow:

43.
Left-Hand Rule Cont’d

44.
The left hand rule to
determine North Pole
NORTH
POLE
SOUTH POLE

45.
Saturation
Saturation
Knee
Y- Axis
Increasin
g
Magnetic
Force
Y
X- Axis Increasing Electric
Current
X
Saturation of a magnetic field occurs when an increase of electric
current flow does not increase the strength of the magnetic field as
shown by the graph. The knee of the curve is the point that
saturation occurs.

46.
MAGNETIC UNITS OF
MEASUREMENT
⚫Magneto-motive Force - the quantity
of magnetic field force, or "push.”
⚫Field Flux - The quantity of total
field effect, or "substance" of the
field.
⚫Field Intensity - The amount of
field force (mmf) distributed over
the length of the electro-magnet.

47.
MAGNETIC UNITS OF
MEASUREMENT Cont’d
⚫Flux Density - The amount of magnetic
field flux concentrated in a given area.
⚫Reluctance - The opposition to
magnetic field flux through a given
volume of space or material.
⚫Permeability - The specific measure of
a material's acceptance of magnetic
flux.

48.
MAGNETIC UNITS OF
MEASUREMENT Cont’d

49.
ELECTROMAGNETIC DEVICES

50.
Electromagnetic Devices

51.
Electromagnetic Devices

52.
MAGNETIC TERMS
⚫Flux - Invisible lines of force.
⚫Poles - North and South where force is
strongest.
⚫Permeability – The ability of a material to
conduct lines of force.
⚫Residual Magnetism – The ability of a
material to hold its magnetism for a long
time.

53.
MAGNETIC TERMS
⚫Ferromagnetic Material – A material easy
to magnetize. (i.e., Iron Steel, Cobalt,
Perm-alloy, and Alnico)
⚫Paramagnetic Material- A material that can
be slightly magnetized.
⚫Diamagnetic Material – A material that is
very difficult to magnetize.
⚫Magnetic Laws – Simply stated: Like poles
repel and unlike poles attract.

54.
Review
⚫What are the poles of a magnet?
⚫Name the magnetic lines of force.
⚫List three types of magnets and their two
families.
⚫List the laws of magnets.
⚫Explain two methods for making a magnet.

55.
Review
⚫Explain two theories of magnetism.
⚫Name five different types of devices
that are associated with
electromagnetism?
⚫List three magnetic and three
nonmagnetic materials.
⚫What will remove magnetic lines of
force?