Magnet Patterns
Topic
The lines of force in a magnetic field
Introduction
A magnet is an object that attracts iron strongly. The area around a magnet
where force is exerted on pieces of iron is called the “magnetic field.” Each end
of a magnet has certain properties and is described as being either a North (N)
pole or a South (S) pole. In this experiment, you will use very small pieces of iron
– iron filings – to “see” the lines of force in the magnetic field around a bar
magnet. You will also observe the lines of force around a pair of magnets when
their poles are close together and look at the differences when different pairs of
poles (N–N, S–S, N–S) are studied.
Time required
30 minutes
Materials
2 bar magnets (approximately 80 × 15 × 10 mm) as in diagram 1 below
poster board (11 × 17 inches)
250 g iron filings in a shaker
sheet of paper
pencil
30 cm ruler
1
South pole
North pole
of magnet
Bar magnet
Safety note
Be careful when handling iron filings – if they are not removed from clothes and
other surfaces quickly they will rust, leaving indelible marks. Wash your hands
at the end of the experiment.
Procedure
1. Place the magnet on a table.
2. Cover the magnet with the poster board so that the magnet is at the center of
the poster board.
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3. Shake iron filings over the poster board in the region of magnet.
4. Hold the top edge of the poster board in place with one hand while tapping
gently against the lower edge. Repeat holding the lower edge and tapping the
top. Repeat for the left and right sides.
5. Observe the pattern of iron filings and draw your observations in box A of the
data table on the next page.
6. Being careful not to spill the iron filings, remove the poster board from over
the magnet. Tip the iron filings onto the sheet of paper and pour them
carefully back into the shaker.
7. Place a second magnet next to the first as shown in diagram 2 below, with the
North poles facing and 2 cm apart.
2
North poles
2 cm
Bar magnets with North poles facing (N–N)
8. Repeat steps 2 to 6, drawing the pattern taken by the iron filings in box B in
the data table.
9. Turn both magnets around so their South poles are facing and position them
2 cm apart (see diagram 3 below).
South poles
3
2 cm
Bar magnets with South poles facing (S–S)
10. Repeat steps 2 to 6, drawing the pattern taken by the iron filings in box C in
the data table.
11. Turn one magnet around so that the North pole of one is facing the South
pole of the other, and position them 2 cm apart (see diagram 4 below).
4
South pole
North pole
2 cm
Bar magnets with opposite poles facing (N–S)
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12. Repeat steps 2 to 6, drawing the pattern taken by the iron filings in box D in
the data table.
DATA
TABLE
A
Pattern made by iron filings above a
single bar magnet
B
Pattern made with two bar magnets,
North poles facing (N–N)
C
Pattern made with two bar magnets,
South poles facing (S–S)
D
Pattern made with two bar magnets,
North pole facing South pole (N–S)
Analysis
1. Describe the pattern made by the iron filings around the single bar magnet
(box A).
2. Is there any difference in the pattern of the iron filings around the single bar
magnet (box A) at each end (or pole)?
3. How did the patterns recorded in boxes B and C compare?
4. Describe the pattern drawn in box D.
5. What can you conclude about the forces at the poles of the magnets?
6. Why is it necessary to tap the poster board on which the iron filings are lying?
Want to know more?
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OUR FINDINGS • 10.34
3. At the end of the experiment, the wire in the fuse has a gap in the center.
There may be a small lump of metal on one of the broken ends of wire. This is
a result of the metal becoming very hot and melting as the current passed
through it before the fuse wire broke and caused the current to stop.
7.09 Electricity Moving Magnets
1. The compass needles all pointed North in the left hand column of the data
table (no current flowing in the wire).
They pointed clockwise when the top wire was connected to the positive pole
of the cell (middle or right-hand column of the data table).
They pointed counterclockwise when the top wire was connected to the
negative pole of the cell (middle or right hand column of the data table).
2. The current (conventional current – positive to negative) was flowing down
the wire when the needles were pointing clockwise.
3. The current (conventional current – positive to negative) was flowing up the
wire when the needles were pointing counterclockwise.
The direction in which the compass needles point indicates the lines of force
exerted by the current carrying wire. The direction is usually remembered by
Maxwell’s corkscrew rule – when driving a corkscrew down into a cork, the
corkscrew has to be turned in a clockwise direction. Thus, if an electric
current (conventional current) passes down a wire, force is exerted in a
clockwise direction around the wire.
Magnetic Effects
8.01 Magnet Patterns
area without iron filings
lines further apart
pole
pole
lines close together
curved lines
Pattern made by the iron filings
around the magnet
Pattern made with the same poles facing
each other
1. The lines form a pattern (see the diagram above left). There are numerous
lines close together at each end of the magnet. These lines radiate from the
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10.35 • OUR FINDINGS
PHYSICS EXPERIMENTS ON FILETM
ends of the magnet, becoming spaced further apart as the distance from the
magnet increases.
Curved lines form along the sides of the magnet, linking the ends. These lines
are further apart as distance from the magnet increases.
The spacing of the lines indicates the strength of the magnetic field. It is
stronger when the lines are close together.
2. The pattern of lines is symmetrical; there is no observable difference between
the ends of the magnet. Both poles of the magnet appear to act in the same
way.
3. The two patterns are the same (see the diagram on the previous page right). In
both cases, opposing poles are next to each other, and it is possible to see
where the lines of force are “pushing” against each other and forcing the lines
apart. Between the magnets there is a space with no iron filings.
4. In box D (opposing poles together), there are lines of iron filings between the
two poles (see diagram below left).
5. Where like poles are together, the area between the two magnets has no lines
of iron filings. This shows that, at the point between two like poles, the force
of one cancels out the other, and there is no magnetic field.
Where unlike poles are together, there are strong lines of iron filings linking
the poles. This shows that there is a strong magnetic field between unlike
poles of two bar magnets.
6. The poster board is tapped so that the iron filings do not stick together and
can move more easily under the influence of the magnetic field.
You could repeat the experiment using magnets of different shapes. Circular
ceramic magnets, which have face poles (they are polarized along their
cylindrical axis), give very dramatic results (see diagram below right)
lines of iron filings
between magnets
Pattern made with opposite poles of magnets
facing each other
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Iron filings sprinkled over a circular
ceramic magnet
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