Lesson overview
Magnets and magnetic fields: What is the invisible pattern around a magnet?
Put a plotting compass by a bar magnet, mark where its needle points, dot by dot, and join the dots into a field line with its arrow; sprinkle iron filings over the magnet, then bring up a second magnet with like and then unlike poles facing, and find the neutral point between two N poles. Then test eight objects to find the magnetic materials, and hang paper clips from a soft-iron rod and a steel rod to see which one stays magnetised.
Suggested sequence
- Lesson 1 · Poles and magnetic fields. Poles, attraction and repulsion; a magnetic field and its direction; field lines plotted with a plotting compass and shown with iron filings; like and unlike poles facing; Supplement: forces as interactions between fields, the neutral point and the spacing of the lines. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · Magnetic materials. Magnetic and non-magnetic materials; induced magnetism; soft iron as a temporary magnet and steel as a permanent one; uses of permanent magnets and electromagnets. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 6 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 7 questions, 15 min, lesson closed.
Learning goals
Part 1: Poles and magnetic fields
- Describe the forces between magnetic poles and between magnets and magnetic materials, including the use of the terms north pole (N pole), south pole (S pole), attraction and repulsion, magnetised and unmagnetised (4.1.1)
- Describe a magnetic field as a region in which a magnetic pole experiences a force (4.1.5)
- Draw the pattern and direction of magnetic field lines around a bar magnet (4.1.6)
- State that the direction of a magnetic field at a point is the direction of the force on the N pole of a magnet at that point (4.1.7)
- Describe the plotting of magnetic field lines with a compass or iron filings and the use of a compass to determine the direction of the magnetic field (4.1.8)
- Supplement: Explain that magnetic forces are due to interactions between magnetic fields (4.1.10)
- Supplement: Know that the relative strength of a magnetic field is represented by the spacing of the magnetic field lines (4.1.11)
Part 2: Magnetic materials
- Describe the forces between magnetic poles and between magnets and magnetic materials, including the use of the terms north pole (N pole), south pole (S pole), attraction and repulsion, magnetised and unmagnetised (4.1.1)
- Describe induced magnetism (4.1.2)
- State the differences between the properties of temporary magnets (made of soft iron) and the properties of permanent magnets (made of steel) (4.1.3)
- State the difference between magnetic and non-magnetic materials (4.1.4)
- Describe the uses of permanent magnets and electromagnets (4.1.9)
Misconceptions to listen for
- “Two N poles attract because they are the same kind.” — The same kind of pole means repulsion: like poles push apart.
- “An N pole and an S pole repel.” — N and S are unlike poles, and unlike poles attract.
- “There is no force until the magnets touch.” — Magnetic forces act across a gap, and they grow stronger as the poles come closer.
- “S pole, because the bottom magnet holds the middle one up.” — A pull from the bottom magnet would drag the middle magnet down onto it. Floating needs a push, and only like poles push.
- “It could be either pole.” — If it were an S pole, the two magnets would attract and snap together. Floating needs repulsion, so it must be N.
- “The face is not a pole.” — The flat faces of a ring magnet are its poles. That is why the rings push on each other.
- “The field is the lines drawn round the magnet.” — The lines are a picture of the field. The field fills the whole region, including the spaces between the lines.
- “The field is where iron filings can be seen.” — Far from the magnet the field is too weak to turn filings, but a compass there still feels a force.
- “The field is only inside the magnet.” — A compass beside the magnet is pushed round, so the field reaches out into the space around it.
- “The field points the way the south end of the needle points.” — The field direction is defined by the force on an N pole, so it is the way the north-seeking end points.
Scope
Forces between magnetic poles and between magnets and magnetic materials, magnetised and unmagnetised (4.1.1); induced magnetism (4.1.2); temporary magnets of soft iron and permanent magnets of steel (4.1.3); magnetic and non-magnetic materials (4.1.4); a magnetic field, the pattern and direction of its lines and their plotting with a compass and iron filings (4.1.5–4.1.8); uses of permanent magnets and electromagnets (4.1.9); Supplement: magnetic forces as interactions between fields (4.1.10) and the strength of a field shown by the spacing of its lines (4.1.11). How a current makes a magnetic field and how an electromagnet is made stronger are in Electromagnets.