Transcript Electricity – Electromagnetism

KS4 Electricity Electromagnetism
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What is a magnetic field?
Where would you find a magnetic field?
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Magnetic field
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
strongest
field at
poles
What does the magnetic field around a bar magnet look like?
Where is the magnetic field strongest?
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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
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Magnets and materials
What materials are magnets made from? Iron or steel.
N
What materials will magnets stick to?
S
Iron or steel.
And nickel!
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Forces between magnets – experiment
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Repulsion and attraction
Repel/attract
Repel/attract
Repel/attract
Unlike poles attract.
Like poles repel.
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Separating coins
How could you separate steel and gold coins using a magnet?
N
S
Steel coins would stick to magnet, gold coins would be left
behind.
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What does the magnetic field for a bar magnet
look like?
In what direction do
field
linesS
Nmagnetic
North to
South
point?
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Revising magnetism I
Iron or steel
Magnets are made from which materials? ___________
What are the ends of a magnet called?
The Poles
__________
What do we call the area around a magnet where a
magnetic force exists?
The Magnetic Field
__________________
What does the word attract mean?
Pull together
__________
Push apart
What does the word repel mean? __________
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Revising magnetism II
Repel
What will two north poles do if brought together? _____
Repel
What will two south poles do if brought together? ______
What will a north and a south pole do if brought
together?
Attract
_______
Iron and steel
What materials are attracted by magnets? ___________
Non-contact
Is magnetism a contact or non-contact force? _________
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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.
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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.
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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
More turns of wire on the coil
Number of
paperclips
Number of batteries
Number of turns
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Electromagnetic strength – experiment
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Electromagnetic strength - results
The results for the number of drawing pins attracted to the
electromagnet with no core are:
number
of cells
number
of coils
4
8
12
1
2
3
2
4
6
4
8
12
6
12
18
How does changing the current affect the strength of
an electromagnet?
How does changing the number of coils affect the strength
of an electromagnet?
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Electromagnetic strength - results
Compare the results for the number of drawing pins attracted
to the electromagnet with no core and an iron core:
number
of cells
number
of coils
4
8
12
1
2
3
2
4
6
4
8
12
6
12
18
number
of cells
number
of coils
4
8
12
1
2
3
6
8
10
8
12
16
10
16
22
What effect does an iron core have on the strength of
an electromagnet?
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Electromagnetic strength - results
Compare the results for the number of drawing pins attracted
to the electromagnet with no core and a copper core:
number
of cells
number
of coils
4
8
12
1
2
3
2
4
6
4
8
12
6
12
18
number
of cells
number
of coils
4
8
12
1
2
3
2
4
6
4
8
12
6
12
18
What effect does a copper core have on the strength of
an electromagnet?
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Ways to make an electromagnet stronger
There are three ways to make an electromagnet
stronger. Do you know them?
More turns on the coil
1. ___________________
More electrical current
2. ___________________
3. ___________________
Using an iron core
S
N
What happens if you turn the battery around in an
electromagnet?
The poles on the coil reverse, north becomes south and
south becomes north.
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What do like poles do?
A. Attract and repel
B. Attract
C. Repel

D. Stick together
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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
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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
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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

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Which of the following is not a use of
electromagnets?
A. Fridge magnets

B. Loud speakers
C. Relays
D. Circuit breakers
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