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KS3 Physics
8J Magnets and
Electromagnets

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8J Magnets and Electromagnets
Contents
Magnetic materials
Magnetic fields
Electromagnets
Summary activities

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Which of the metals below are magnetic metals?
aluminium (Al)
silver (Ag)
iron
(Fe)
gold (Au)
nickel (Ni)
cobalt (Co)
copper (Cu) zinc (Zn)
magnesium
(Mg)
Magnetic materials

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N
S
Al ZnAg
Cu
Au
Mg
Fe
Ni
Co
A magnetic material is attracted to a magnet.
Magnetic materials
Only iron (Fe), nickel (Ni) and cobalt (Co) are magnetic.

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8J Magnets and Electromagnets
Contents
Magnetic materials
Magnetic fields
Electromagnets
Summary activities

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Forces between magnets – experiment

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NS
The iron filings feel the effect of the magnetic field and
show the direction of the forces in this region.
The region around a magnet where it has a magnetic effect
is called its magnetic field.
When a magnetic material is placed in a magnetic field it will
experience a force.
What is a magnetic field?

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weakest field further
away from poles
What is the shape and direction of the lines of force in the
magnetic field around a bar magnet?
N S
Shape of a magnetic field
Where is the magnetic field strongest?
strongest
field
at poles
strongest
field
at poles

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Bring the north poles of two bar magnets together.
What happens to the magnets?
Viewing magnetic fields: N poles together
N SS N
Next, bring the two north poles as close to each other as
possible and place a piece of paper on top of the magnets.
Carefully scatter iron filings onto the paper.
Draw the pattern created by the iron filings.

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NNS S
Magnetic field pattern: N poles together
What do you notice about the pattern of the lines of
force in the region between the two north poles?

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Bring the north and south poles of two bar magnets together.
What happens to the magnets?
Viewing magnetic fields: N and S poles together
S N S N
Next, put the north and south poles close to each other,
without letting them touch, and place a piece of paper on top.
Carefully scatter iron filings onto the paper.
Draw the pattern created by the iron filings.

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NN
How does this pattern compare with the pattern between
the two north poles?
Magnetic field pattern: N and S poles together
What do you notice about the pattern of the lines of
force in the region between the north and south poles?
S S

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1. When two like poles (e.g. two north poles or two south
poles) are put together, they repel each other.
Magnetic fields – summary
2. When two unlike poles (e.g. a north and a south pole)
are put together, they attract each other.
3. Scattering iron filings around a bar magnets makes it
possible to see the lines of force of the magnetic field.

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A magnet can be made by magnetizing a material which is
attracted to a magnet, e.g. a paper clip.
Stroke a magnet along the paperclip from one end to the
other and then starting from the same place, repeat the
movement. The more times this is done, the more
magnetic the clip becomes.
Hold a nail in a magnetic field and hit it with a hammer.
Put a magnetic material in a strong magnetic field.
Making a magnet
There are three methods that can be used to make a magnet:

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8J Magnets and Electromagnets
Contents
Magnetic materials
Magnetic fields
Electromagnets
Summary activities

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Making an electromagnet
When electricity is passed through a coil of wire, the coil has
a magnetic field around it. This is called an electromagnet.
If the coil of wire is wrapped around a piece of iron, such as
an iron nail, the magnetic field gets stronger.

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An iron core at the centre of a coil of wire, increases the
strength of an electromagnet.
Two experiments can be carried out to investigate the other
factors that can affect the strength of an electromagnet:
Investigating an electromagnet
1. Investigate how the number of coils affects the
number of paper clips attracted to an electromagnet
– keep the current the same in this experiment.
2. Investigate how the size of the current affects the
number of paper clips attracted to an electromagnet
– keep the number of coils the same in this experiment.

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Number of coils
Number of paper
clips attracted
0
20
40
60
80
Remember – keep the current the same
throughout this experiment!
Investigating an electromagnet – results 1
0
8
18
31
46

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Current (A)
Number of paper
clips attracted
0
1
2
3
4
5
Remember – keep the number of coils the same
throughout this experiment!
Investigating an electromagnet – results 2
0
12
23
38
49
60

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Graph to show how the number of coils affects
the strength of an electromagnet
0
10
20
30
40
50
0 20 40 60 80 100
number of coils
numberofclipsattracted
Investigating an electromagnet – graph 1

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Graph to show how the current affects the
strength of an electromagnet
0
10
20
30
40
50
60
70
0 1 2 3 4 5
current (A)
numberofclipsattracted
Investigating an electromagnet – graph 2

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What advantages does
an electromagnet have
over a permanent
magnet?
What metals would the
electromagnet attract?
A large electromagnet is used in a scrap yard to pick up
and move heavy pieces of scrap metal.
Using electromagnets – scrap yards

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The circuit for a door bells includes an electromagnet.
Using electromagnets – door bells

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Lifts, cars and other large electrical machines use high
currents.
Using electromagnets – relay
A relay, which includes an electromagnet, is used to allow
a small current in one circuit to control a large current in
another circuit.

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1. When electricity is passed through a coil of wire, the coil
behaves like a magnet and has a magnetic field around it
– this is an electromagnet.
Electromagnets – summary
 wrap the coil of wire around an iron core;
 increase the number of coils;
 increase the size of the current.
3. An electromagnet can be easily turned on and off.
This is why electromagnets can be used in
scrapyards and as switches in electrical devices.
2. There are three ways to make an electromagnet stronger:

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8J Magnets and Electromagnets
Contents
Magnetic materials
Magnetic fields
Electromagnets
Summary activities

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Glossary
attraction – The force that pulls things together,
e.g. opposite poles of two magnets.
electromagnet – A magnet made by passing electricity
through a coil of wire, which often has a core inside.
magnet – An object that has a magnetic field and can
attract magnetic materials.
magnetic field – The area around a magnet where its
magnetic force can be felt.
magnetic materials – Materials that are attracted to a
magnet, e.g. iron, cobalt and nickel.
magnetism – The non-contact force of a magnetic field.
poles – The parts of a magnet where its magnetic field is
strongest.
repulsion – The force that pushes things away from each
other, e.g. similar poles of two magnets.

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Anagrams

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Multiple-choice quiz