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The
discovery
of
electricity
Magnetism
Before learning about electricity, we must first understand
magnetism, for without magnets we could not be living in
today’s electrical age.
Bodies which attract iron are called magnets and the mineral
magnetite, sometimes called lodestone, is a magnet in its
natural state. The metals iron, nickel and cobalt are not
natural magnets, but they can be made into magnets or
“magnetised”. Most magnets are made of iron because this
metal can be magnetised more strongly than the others.
1
The discovery of electricity fact
sheets reviewed and updated with
the assistance of STAV Publishing
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2
The magnetic field
A magnet influences all magnetic materials near it and the region in
which the influence is felt is called a magnetic field.
The simplest form of magnet is a bar magnet. The shape of its
magnetic field can be made visible by a simple experiment.
Activity
Cover the bar magnet with a sheet of paper and then
sprinkle the paper with iron filings. Tap the paper lightly.
What happens?
Now try this experiment with two magnets as shown here.
<3D magnetic
field activity>
<Teachers
Notes>
When the paper is tapped lightly, the filings arrange themselves
in a symmetrical pattern of curved lines. These “lines of force”
show the regions of the magnet’s influence throughout the
magnetic field.
The familiar “horseshoe” magnet is a bar magnet which has been
bent to bring the two ends close together. This intensifies the
magnetic field between the ends.
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How the magnetic compass works
If a light bar magnet which is free to rotate on a pivot is placed in a
magnetic field, the magnet will lie parallel to the lines of force.
The simple compass works in this fashion as the earth
is a huge magnet with its magnetic field lying
approximately north and south.
SIMPLE COMPASS SHOWS LINES OF
FORCE NEAR END OF BAR MAGNET.
<Make a compass>
When a magnetic compass is held near a wire carrying an electric
current, the compass needle is deflected and this shows that there
is a magnetic field near the wire. The field near a straight wire is too
weak for most purposes, but if the wire is wound into a coil, the same
current will produce a much stronger field. The field may be made
stronger still by placing an iron core in the coil.
A core of iron placed in a coil through
which a current is flowing becomes a
magnet. This is the usual method of
making “permanent” magnets, as the
iron will retain some of its magnetism
when taken out of the coil.
MAGNETIC FIELD AROUND WIRE THROUGH
WHICH ELECTRIC CURRENT FLOWS IS
SHOWN BY IRON FILINGS AND COMPASS
Electro-magnets
A magnet which derives its magnetism from the current in a wire coiled
around it is called an electro-magnet.
<Electromagnetism
activity>
3
An electro-magnet can be made much stronger than a permanent
magnet. It also has the advantage that the strength of the field may
be changed by varying the number of turns in the coil or by altering
the current in the coil. Electro-magnets are the basis of our modern
electric generators, electric motors, radios, telephones and hundreds
of electrical machines and appliances. Some of these magnets are
so large and powerful that scientists operating them must use special
boots with non-magnetic nails, otherwise they would not be able to
walk freely.
Electro-magnets are used for removing pieces of iron from moving
streams of material such as cement, coal and foodstuffs and recently
have proved a great aid to eye surgeons when removing foreign bodies
from the eye.
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4
The electric motor
The most useful application of electricity and magnetism is the
electric motor.
In the electric motor, current in a coil causes it to move in a magnetic
field. Current in the moving coil called the rotor, causes it to turn
at right angles to the magnetic field (normally an electro-magnet)
by means of a special contact system called a commutator, the
rotor keeps rotating in the same direction. Thus electrical energy is
converted into mechanical energy.
CURRENT FLOW
DIRECTION OF
ROTATION
ELECTRICITY IS
GENERATED IN A
COIL WHICH ROTATES
IN THE FIELD OF AN
ELECTRO-MAGNET OF
SPECIAL SHAPE.
More on magnetism
Check these websites for more information about magnetism.
Sketches of a History of Classical Electromagnetism (an overview of
developments in electricity, magnetism and other related phenomena)
<http://history.hyperjeff.net/electromagnetism.html>
Maxwell’s Equations (an overview of the maths that led to the theory
of electromagnetism)
<http://www.mathdaily.com/lessons/Maxwell%27s_equations>
Cool Magnet Man (all sorts of experiments and activities to do with
magnets)
<http://www.coolmagnetman.com/>
Magnetism: information and quiz
<http://www.school-for-champions.com/science/magnetism.htm>
Experiments about magnetism
<http://www.galaxy.net/~k12/electric/index.shtml>
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The 3D Magnetic Field Activity
The magnetic field is not just a 2-dimensional phenomenon.
It travels in all directions.
Try this:
Fill a small PET bottle (about 300ml) with cooking oil.
Carefully add 1-2 teaspoons of iron filings, and screw the lid
on tight. Hold a magnet to the outside of the bottle, and see
what happens!
Do you want
to try some other
magnetism activities?
<Make a compass>
<Electromagnetism
activity>
5
Activity written by Michaela Patel
on behalf of STAV publishing.
Make a compass Activity
You can make your own compass from very simple materials and
use it to investigate other aspects of electromagnetism.
6
Try this:
• An iron needle
• A bar magnet
• A small piece of polystyrene foam
• A saucer of water
What to do
• First, magnetise your needle by stroking it in the same
direction with the magnet 20 times
• Gently push the needle through the piece of foam so it sticks
out both sides evenly
Do you want
to try some other
magnetism activities?
• Float the foam with the needle on the dish of water. It should
float in the middle of the dish. If it doesn’t, add more water to
the dish so the water meniscus ( curved surface at the top) is
just above the edges of the dish.
Explore
What happens when you place a magnet near your compass?
<The 3D Magnetic
Field activity>
How close does the magnet need to be to the compass for an
effect to be observed?
If you can get a piece of haematite, see what happens when this
is placed near the magnet.
Class extension
<Electromagnetism
activity>
Activity written by Michaela Patel
on behalf of STAV publishing.
Place a large bar magnet in the centre of the table. Place
everyone’s needle compasses around the magnet. Which
way do the compasses point?
electromagnetism
Activity
Electromagnets can be much stronger than permanent
magnets, but how do they work?
Make a simple electromagnet to find out.
You will need:
• Batteries: 9 Volt, 6 Volt, AA size, D size
• A coil of insulated copper wire
• A large iron nail
• Iron paper clips
7
• Other magnets
What to do
• Wrap the copper wire several turns around the iron nail
• Connect the ends of the wire to the opposite poles of
your battery.
Do you want
to try some other
magnetism activities?
• Try to pick up a paper clip by touching the nail inside the
coil to the clip.
Explore
Is there a relationship between number of coils of wire and
strength of your electromagnet?
<Make a compass>
<The 3D Magnetic
Field activity>
Activity written by Michaela Patel
on behalf of STAV publishing.
How does voltage affect the strength of the electromagnet?
Teachers notes
The 3D Magnetic Field Activity
The viscous oil prevents the iron filings from
settling too quickly. This activity demonstrates the
3-dimensional nature of the magnetic field,
something often passed over in standard
demonstrations using iron filings sprinkled on
paper with a magnet held underneath.
Activity written by Michaela Patel
on behalf of STAV publishing.
Magnetism
Before learning about electricity, we
must first understand magnetism,
for without magnets we could not be
living in today’s electrical age.
Bodies which attract iron are called
magnets and the mineral magnetite,
sometimes called lodestone, is a
magnet in its natural state. The metals
iron, nickel and cobalt are not natural
magnets, but they can be made
into magnets or “magnetised”. Most
magnets are made of iron because this
metal can be magnetised more strongly
than the others.
The magnetic field
A magnet influences all magnetic materials
near it and the region in which the influence
is felt is called a magnetic field.
The simplest form of magnet is a bar
magnet. The shape of its magnetic field can
be made visible by a simple experiment.
How the magnetic
compass works
If a light bar magnet which is free to rotate
on a pivot is placed in a magnetic field, the
magnet will lie parallel to the lines of force.
The simple compass works in this fashion
as the earth is a huge magnet with its
magnetic field lying approximately north
and south.
When a magnetic compass is held near
a wire carrying an electric current, the
compass needle is deflected and this
shows that there is a magnetic field near
the wire. The field near a straight wire is
too weak for most purposes, but if the wire
is wound into a coil, the same current will
produce a much stronger field. The field
may be made stronger still by placing an
iron core in the coil.
A core of iron placed in a coil through which
a current is flowing becomes a magnet. This
is the usual method of making “permanent”
magnets, as the iron will retain some of its
magnetism when taken out of the coil.
Electro-magnets
A magnet which derives its magnetism from
the current in a wire coiled around it is called
an electro-magnet.
An electro-magnet can be made much
stronger than a permanent magnet. It also
has the advantage that the strength of the
field may be changed by varying the number
of turns in the coil or by altering the current
in the coil. Electro-magnets are the basis
of our modern electric generators, electric
motors, radios, telephones and hundreds
of electrical machines and appliances.
Some of these magnets are so large and
powerful that scientists operating them
must use special boots with non-magnetic
nails, otherwise they would not be able to
walk freely.
Electro-magnets are used for removing
pieces of iron from moving streams
of material such as cement, coal and
foodstuffs and recently have proved a great
aid to eye surgeons when removing foreign
bodies from the eye.
More on magnetism
Check these websites for more
information about magnetism.
Sketches of a History of Classical
Electromagnetism (an overview of
developments in electricity, magnetism and
other related phenomena)
<http://history.hyperjeff.net/
electromagnetism.html>
Maxwell’s Equations (an overview of
the maths that led to the theory of
electromagnetism)
<http://www.mathdaily.com/lessons/
Maxwell%27s_equations>
Cool Magnet Man (all sorts of experiments
and activities to do with magnets)
<http://www.coolmagnetman.com/>
Magnetism: information and quiz
<http://www.school-for-champions.com/
science/magnetism.htm>
Experiments about magnetism
<http://www.galaxy.net/~k12/electric/index.
shtml>
The electric motor
The most useful application of electricity and
magnetism is the electric motor.
In the electric motor, current in a coil causes
it to move in a magnetic field. Current in
the moving coil called the rotor, causes
it to turn at right angles to the magnetic
field (normally an electro-magnet) by
means of a special contact system called a
commutator, the rotor keeps rotating in the
same direction. Thus electrical energy is
converted into mechanical energy.
The discovery of electricity
fact sheets reviewed and
updated with the assistance
of STAV Publishing