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8/22/2019 KS4+Electricity+ +Electromagnetism
http://slidepdf.com/reader/full/ks4electricity-electromagnetism 1/24
© Boardworks Ltd 2005
KS4 Electricity -
Electromagnetism
8/22/2019 KS4+Electricity+ +Electromagnetism
http://slidepdf.com/reader/full/ks4electricity-electromagnetism 2/24
© Boardworks Ltd 2005
What is a magnetic field?
Where would you find a magnetic field?
8/22/2019 KS4+Electricity+ +Electromagnetism
http://slidepdf.com/reader/full/ks4electricity-electromagnetism 3/24
© Boardworks Ltd 2005
Around every magnet is an invisible force field that will affect
all magnetic objects inside it.
The magnetic field of a bar magnet is seen with iron filings.
N S
Magnetic field
What does the magnetic field around a bar magnet look like?
strongest
field at
poles
Where is the magnetic field strongest?
8/22/2019 KS4+Electricity+ +Electromagnetism
http://slidepdf.com/reader/full/ks4electricity-electromagnetism 4/24
© Boardworks Ltd 2005
What materials will stick to magnets?
Look around the laboratory or your
teacher will provide a tray.
See which materials will stick to a magnet
and which materials will not.
Magnetic
materials
Non-magnetic
materials
8/22/2019 KS4+Electricity+ +Electromagnetism
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© Boardworks Ltd 2005
Magnets and materials
N S
What materials are magnets made from? Iron or steel.
What materials will magnets stick to? Iron or steel.
And nickel!
8/22/2019 KS4+Electricity+ +Electromagnetism
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© Boardworks Ltd 2005
Forces between magnets – experiment
8/22/2019 KS4+Electricity+ +Electromagnetism
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Repulsion and attraction
Repel/attract
Repel/attract
Repel/attract
Unlike poles attract.
Like poles repel.
8/22/2019 KS4+Electricity+ +Electromagnetism
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© Boardworks Ltd 2005
Separating coins
N S
How could you separate steel and gold coins using a magnet?
Steel coins would stick to magnet, gold coins would be left
behind.
8/22/2019 KS4+Electricity+ +Electromagnetism
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What does the magnetic field for a bar magnet
look like?
In what direction domagnetic field lines
point?N North to South S
8/22/2019 KS4+Electricity+ +Electromagnetism
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© Boardworks Ltd 2005
Revising magnetism I
Magnets are made from which materials? ___________
What are the ends of a magnet called? __________
What do we call the area around a magnet where a
magnetic force exists? __________________ What does the word attract mean? __________
What does the word repel mean? __________
Iron or steel
The Poles
The Magnetic Field
Pull together
Push apart
8/22/2019 KS4+Electricity+ +Electromagnetism
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© Boardworks Ltd 2005
What will two north poles do if brought together? _____
What will two south poles do if brought together? ______
What will a north and a south pole do if brought
together? _______
What materials are attracted by magnets? ___________
Is magnetism a contact or non-contact force? _________
Repel
Repel
Attract
Iron and steel
Non-contact
Revising magnetism II
8/22/2019 KS4+Electricity+ +Electromagnetism
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Electromagnets
A coil of wire acts like a bar magnet when it has an
electric current flowing through it.
One end of the coil becomes a north-seeking pole.
One end of the coil becomes a south seeking pole.
This is called an electromagnet.
8/22/2019 KS4+Electricity+ +Electromagnetism
http://slidepdf.com/reader/full/ks4electricity-electromagnetism 13/24© Boardworks Ltd 2005
Making an electromagnet:
Apparatus:
Batteries
Wire
Iron Nail
What to do:
1. Wrap a coil of wire around the iron nail.
2. Connect the coil of wire to the batteries.
3. See how many paperclips you can pick up.
8/22/2019 KS4+Electricity+ +Electromagnetism
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Results
How many paperclips could you pick up?
Can you think of any ways to make the electromagnet
pick up more paperclips?
More batteries (more current)
Number of
paperclips
Number of batteries
More turns of wire on the coil
Number of
paperclips
Number of turns
8/22/2019 KS4+Electricity+ +Electromagnetism
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Electromagnetic strength – experiment
8/22/2019 KS4+Electricity+ +Electromagnetism
http://slidepdf.com/reader/full/ks4electricity-electromagnetism 16/24© Boardworks Ltd 2005
The results for the number of drawing pins attracted to the
electromagnet with no core are:
Electromagnetic strength - results
1 2 3
4 2 4 6
8 4 8 12
12 6 12 18
number of cells
number of coils
How does changing the current affect the strength of an electromagnet?
How does changing the number of coils affect the strength
of an electromagnet?
8/22/2019 KS4+Electricity+ +Electromagnetism
http://slidepdf.com/reader/full/ks4electricity-electromagnetism 17/24© Boardworks Ltd 2005
Compare the results for the number of drawing pins attracted
to the electromagnet with no core and an iron core:
Electromagnetic strength - results
1 2 3
4 2 4 6
8 4 8 1212 6 12 18
number of cells
number of coils
1 2 3
4 6 8 10
8 8 12 1612 10 16 22
number of cells
number of coils
What effect does an iron core have on the strength of
an electromagnet?
8/22/2019 KS4+Electricity+ +Electromagnetism
http://slidepdf.com/reader/full/ks4electricity-electromagnetism 18/24© Boardworks Ltd 2005
Compare the results for the number of drawing pins attracted
to the electromagnet with no core and a copper core:
Electromagnetic strength - results
1 2 3
4 2 4 6
8 4 8 12
12 6 12 18
number of cells
number of coils
1 2 3
4 2 4 6
8 4 8 12
12 6 12 18
number of cells
number of coils
What effect does a copper core have on the strength of
an electromagnet?
W k l
8/22/2019 KS4+Electricity+ +Electromagnetism
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Ways to make an electromagnet stronger
There are three ways to make an electromagnet
stronger. Do you know them?1. ___________________
2. ___________________
3. ___________________
More turns on the coil
More electrical current
Using an iron core S N
What happens if you turn the battery around in an
electromagnet?
S
The poles on the coil reverse, north becomes south and
south becomes north.
8/22/2019 KS4+Electricity+ +Electromagnetism
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What do like poles do?
A. Attract and repel
B. Attract
C. Repel
D. Stick together
8/22/2019 KS4+Electricity+ +Electromagnetism
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Which material below will not stick to a magnet?
A. Steel paper clip
B. Aluminium can
C. Iron nail
D. Steel key
8/22/2019 KS4+Electricity+ +Electromagnetism
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Which of the below will not increase the
strength of an electromagnet?
A. More coils
B. More current
C. Less current
D. Iron core
8/22/2019 KS4+Electricity+ +Electromagnetism
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In which direction do magnetic field lines
always point?
A. East to west
B. West to east
C. South to north
D. North to south