8 j magnets & electromagnets (boardworks)

KS3 Physics

8J Magnets and
Electromagnets
1 of 29
20

© Boardworks Ltd 2004
2005

Contents

8J Magnets and Electromagnets
Magnetic materials
Magnetic fields
Electromagnets
Summary activities
1 of 29
20
2

2005

Magnetic materials
Which of the metals below are magnetic metals?

iro
n

(F
e)

co
ba
lt

ne
ag
m
1 of 29
20
3

co
pp
er
i um
s

(

g)
M

gold
(A

(C
o)

(Cu

)

u)

ni
ck
z

c (Zn)
in

silver (Ag)

lum
a

el

(N
i)

(Al)
nium
i

2005

Magnetic materials
A magnetic material is attracted to a magnet.
Only iron (Fe), nickel (Ni) and cobalt (Co) are magnetic.

S
N N
i

Co

Fe

Au

Mg

1 of 29
20
4

Cu

Ag

Al

Zn
2005

Contents

Magnetic materials
Magnetic fields
Electromagnets
Summary activities
1 of 29
20
5

2005

Forces between magnets – experiment

1 of 29
20
6

2005

What is a magnetic field?
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.

S

N

The iron filings feel the effect of the magnetic field and
show the direction of the forces in this region.
1 of 29
20
7

2005

Shape of a magnetic field
What is the shape and direction of the lines of force in the
magnetic field around a bar magnet?

strongest
field
at poles

N

S

strongest
field
at poles

weakest field further
away from poles
Where is the magnetic field strongest?
1 of 29
20
8

2005

Viewing magnetic fields: N poles together
Bring the north poles of two bar magnets together.

S

N

N

S

What happens to the magnets?
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.

1 of 29
20
9

2005

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?

S

1 of 20
10 of 29

N

N

S

2005

Viewing magnetic fields: N and S poles together
Bring the north and south poles of two bar magnets together.

S

N

S

N

What happens to the magnets?
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.

1 of 20
11 of 29

2005

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

N

S

N

How does this pattern compare with the pattern between
the two north poles?
1 of 20
12 of 29

2005

Magnetic fields – summary
1. When two like poles (e.g. two north poles or two south
poles) are put together, they repel each other.

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.

1 of 20
13 of 29

2005

Making a magnet
A magnet can be made by magnetizing a material which is
attracted to a magnet, e.g. a paper clip.
There are three methods that can be used to make a magnet:
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.

1 of 20
14 of 29

2005

Contents

Magnetic materials
Magnetic fields
Electromagnets
Summary activities
1 of 20
15 of 29

2005

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.

1 of 20
16 of 29

2005

Investigating an electromagnet
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:

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.
1 of 20
17 of 29

2005

Investigating an electromagnet – results 1
Number of coils

Number of paper
clips attracted

0

0

20

8

40

18

60

31

80

46

Remember – keep the current the same
throughout this experiment!
1 of 20
18 of 29

2005

Investigating an electromagnet – results 2

Current (A)

Number of paper
clips attracted

0

0

1

12

2

23

3

38

4

49

5

60

Remember – keep the number of coils the same
throughout this experiment!
1 of 20
19 of 29

2005

Investigating an electromagnet – graph 1
Graph to show how the number of coils affects
the strength of an electromagnet
number of clips attracted

50
40
30
20
10
0
0

1 of 20
20 of 29

20

40
60
number of coils

80

100

2005

Investigating an electromagnet – graph 2

number of clips attracted

70

Graph to show how the current affects the
strength of an electromagnet

60
50
40
30
20
10
0
0

1 of 20
21 of 29

1

2

3

current (A)

4

5

2005

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

1 of 20
22 of 29

2005

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

1 of 20
23 of 29

2005

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

1 of 20
24 of 29

2005

Electromagnets – summary
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.

2. There are three ways to make an electromagnet stronger:
 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.

1 of 20
25 of 29

2005

Contents

Magnetic materials
Magnetic fields
Electromagnets
Summary activities
1 of 20
26 of 29

2005

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.
1 of 20
27 of 29

2005

Anagrams

1 of 20
28 of 29

2005

Multiple-choice quiz

1 of 20
29 of 29

2005

8 j magnets & electromagnets (boardworks)

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (20)

Similar to 8 j magnets & electromagnets (boardworks)

Similar to 8 j magnets & electromagnets (boardworks) (20)

More from cartlidge

More from cartlidge (20)

Recently uploaded

Recently uploaded (20)

8 j magnets & electromagnets (boardworks)