1 of 40© Boardworks Ltd 2008 Magnetic effects of current.
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Transcript of 1 of 40© Boardworks Ltd 2008 Magnetic effects of current.
1 of 40 © Boardworks Ltd 2008
Magnetic effects of current
2 of 40 © Boardworks Ltd 2008
Making an electromagnet
3 of 40 © Boardworks Ltd 2008
Investigating electromagnets
The strength of an electromagnet depends on whether it has a core of iron.
Two experiments can be carried out to investigate the other factors that can affect the strength of an electromagnet:
Investigate how the number of coils affects the number of drawing pins attracted to an electromagnet – keep the current the same in this experiment.
Investigate how the size of the current affects the number of drawing pins attracted to an electromagnet – keep the number of coils the same in this experiment.
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How could you use the apparatus below to investigate the effects of changing the current and the number of coils on the strength of an electromagnet?
Investigating electromagnets
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Investigating electromagnets – results
Here are some example results.
0
8
18
31
46
0
20
40
60
80
number of coils
number of drawing pins
attracted
0
12
23
38
49
0
1
2
3
4
current (A)
number of drawing pins
attracted
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50
40
30
20
10
0
20 40 60 80 1000
number of coils
num
ber
of d
raw
ing
pin
s a
ttra
cte
dInvestigating electromagnets – analysis
How did the number of coils affect the number of drawing pins attracted to the electromagnet?
7 of 40 © Boardworks Ltd 2008
Investigating electromagnets – analysis
How did the size of the current affect the number of drawing pins attracted to the electromagnet?
60
40
30
20
10
0
1 2 3 4 50
current (A)
num
ber
of d
raw
ing
pin
s a
ttra
cte
d
50
8 of 40 © Boardworks Ltd 2008
Using electromagnets – recycling
A large electromagnet is used on a recycling plant conveyor belt to pick up and move metal cans.
What advantages does an electromagnet have over a permanent magnet?
Which metals would the electromagnet attract?
9 of 40 © Boardworks Ltd 2008
Uses of electromagnets – electric bell
When the circuit is closed, the electromagnet pulls the armature towards it, causing the hammer to strike the bell.
The movement of the armature breaks the circuit, and the hammer returns to its original position.
This sequence repeats, causing the bell to sound continuously.
The circuit for a door bell includes an electromagnet.
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Label the diagram – electric bell
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Using electromagnets – door bells
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Lifts, cars and other large electrical machines use high currents.
Relays use an electromagnet to allow a small current in one circuit to control a large current in another circuit.
Can you predict what will happen when the switch is closed in this circuit?
Using electromagnets – the relay
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Label the diagram – relay
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Electromagnets: summary
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Glossary
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Anagrams
