Investigating Magnetism and Magnetic Fields

Aim

To investigate the magnetic field pattern and direction around a bar magnet using iron filings and small compasses.

Learning Outcome

• Identify the north and south poles of a magnet.
• Observe magnetic field patterns around a bar magnet.
• Determine the direction of magnetic field lines.
• Explain attraction and repulsion between magnetic poles.
• Identify regions where the magnetic field is strongest.
• Use iron filings and compasses to represent magnetic fields.

Time Allocation

• Experiment 1: Approximately 20 minutes.
• Experiment 2: Approximately 30 minutes.

How Does It Work?

A magnet produces an invisible magnetic field around it. This magnetic field can attract magnetic materials such as iron.

Every bar magnet has two poles: a north pole and a south pole.

Iron filings become temporarily magnetised when placed in a magnetic field. The filings align themselves along the magnetic field lines, making the invisible magnetic field visible.

Small compasses can also be used to determine the direction of the magnetic field. The compass needle aligns itself with the magnetic field lines.

The magnetic field is strongest near the poles of the magnet, where the field lines are closest together.

Scientific Background

A magnetic field is the region around a magnet where magnetic forces can be detected.

Magnetic field lines are used to represent the shape and direction of the magnetic field.

Important Properties of Magnetic Field Lines

• Field lines point from the north pole to the south pole outside the magnet.
• Field lines are closer together where the magnetic field is strongest.
• Field lines never cross.
• Field lines form continuous loops.

The magnetic field around a magnet can pass through materials such as paper and plastic.

Hypothesis

If iron filings or small compasses are placed around a bar magnet, then they will show the pattern and direction of the magnetic field around the magnet.

Variables

Independent Variable

Position around the magnet.

Dependent Variables

• Pattern of iron filings.
• Direction of compass needles.

Control Variables

• Same bar magnet.
• Same amount of iron filings.
• Same paper or transparency sheet.
• Same type of compass.
• Same setup surface.

Experiment 1: Observing the Magnetic Field Around a Bar Magnet

Aim

To observe the magnetic field pattern around a bar magnet.

Apparatus

• 2 × bar magnets
• Demonstrator plate
• Transparency sheet, A4 size
• White paper, A4 size
• Pencil
• Iron filings

Safety Precautions

Method

1. Place the bar magnet on top of the demonstrator plate or flat surface.
2. Cover the magnet with the transparency sheet or white paper.
3. Mark the positions of the north and south poles on the paper.
4. Sprinkle a small amount of iron filings evenly over the paper.
5. Gently tap the paper with a pencil to help the iron filings align themselves with the magnetic field lines.
6. Observe the pattern formed by the iron filings.
7. Identify where the field lines are closest together.
8. Turn the magnet sideways and repeat the investigation.
9. Compare the different magnetic field patterns observed.
10. Sketch the magnetic field pattern in your notebook.

Results Table

Observation	Description
Shape of field lines
Area where filings are closest together
Strongest part of magnetic field
Effect of changing magnet position

What Learners Should Observe

• The iron filings form curved lines around the magnet.
• The magnetic field pattern becomes visible.
• More iron filings gather near the poles.
• The magnetic field is strongest near the poles.
• Fewer filings gather near the centre of the magnet.

Expected Results

The iron filings should form a clear magnetic field pattern around the bar magnet.

The field lines should appear strongest near the north and south poles where the filings are closest together.

Conclusion

A bar magnet produces a magnetic field around it. Iron filings align themselves along the magnetic field lines, making the invisible magnetic field visible.

The magnetic field is strongest near the poles of the magnet.

Experiment 2: Determining the Direction of the Magnetic Field

Aim

To determine the direction of the magnetic field lines around a bar magnet using small compasses.

Apparatus

• 2 × bar magnets
• Small compasses
• Demonstrator plate
• Transparency sheet, A4 size
• Pencil
• White paper

Safety Precautions

• Handle compasses carefully.
• Keep magnets away from sensitive electronic devices.
• Do not place compasses too close together.
• Keep the work area clean and organised.

Method

1. Place the bar magnet on top of the demonstrator plate or flat surface.
2. Place the transparency sheet or white paper over the magnet.
3. Draw the outline of the magnet on the paper.
4. Mark the north and south poles.
5. Place a small compass near one end of the magnet.
6. Gently tap the compass to allow the needle to align with the magnetic field.
7. Mark the direction of the compass needle on the paper.
8. Move the compass so that its tail is positioned where the previous arrow ended.
9. Repeat the process until the other end of the magnet is reached.
10. Join the marked points to draw the magnetic field line.
11. Repeat the process at several positions around the magnet.
12. Draw arrows on the field lines to indicate the direction of the magnetic field.

Results Table

Position Around Magnet	Compass Direction	Field Direction
Near north pole
Near south pole
Side of magnet
Further away from magnet

What Learners Should Observe

• Compass needles align themselves with the magnetic field.
• Magnetic field lines point from the north pole to the south pole outside the magnet.
• Field lines curve around the magnet.
• Field lines are closer together near the poles.

Expected Results

The compasses should indicate the direction of the magnetic field around the bar magnet.

The magnetic field lines should form curved paths from the north pole to the south pole.

Conclusion

Small compasses can be used to determine the direction of magnetic field lines around a bar magnet.

The magnetic field lines outside the magnet point from the north pole to the south pole.

Questions for Learners

1. What is a magnetic field?
2. Where is the magnetic field strongest around a bar magnet?
3. What do iron filings show?
4. What do compasses show?
5. Why are field lines closer together near the poles?
6. Why do magnetic field lines never cross?
7. What happens when like poles face each other?
8. What happens when opposite poles face each other?
9. Why do iron filings align themselves in a pattern?
10. Why is the magnetic field called invisible?

Common Mistakes

• Using too many iron filings.
• Shaking the paper too aggressively.
• Forgetting to mark the poles.
• Drawing field lines without arrows.
• Allowing iron filings to stick directly to the magnet.
• Confusing the pattern shown by iron filings with field direction shown by compasses.

Teacher Notes

• This investigation works well as a teacher demonstration or group practical.
• Iron filings show the shape of the magnetic field while compasses show the direction.
• Use small amounts of iron filings for clearer patterns.
• Demonstrate attraction and repulsion using two bar magnets before starting the investigation.
• Encourage learners to draw neat field line diagrams with arrows.

Teacher Tip

Extension Activity

Ask learners to investigate:

• the field pattern between two opposite poles,
• the field pattern between two like poles,
• the field pattern around a horseshoe magnet.

Learners can compare how different magnets produce different magnetic field patterns.

Real-World Application

Magnetic fields are used in compasses, electric motors, generators, speakers, magnetic door catches, MRI scanners and navigation systems.

Understanding magnetic fields helps learners understand later topics such as electromagnetism and electric motors.