Bringing together two sets of constraints

Focusing on the learners:

Distinguishing–eliciting–connecting. How to:

• connect magnetic effects to permanent magnets
• show pupils how to see fields
• keep magnetic effects separate from gravitational effects
• distinguish action at a distance from action by contact

Teacher Tip: These are all related to findings about children's ideas from research. The teaching activities will provide some suggestions. So will colleagues, near and far.

Focusing on the physics:

Representing–noticing–recording. How to:

• introduce, discuss and use the idea of a field
• represent a pole
• account for north and south poles
• build a way of thinking about permanent magnets that supports pupils being able to make predictions

Teacher Tip: Connecting what is experienced with what is written and drawn is essential to making sense of the connections between the theoretical world of physics and the lived-in world of the children. Don't forget to exemplify this action.

Not all metals are magnetic

Wrong Track: All metals are magnetic, magnets will stick to any metal!

Right Lines: Most metals are not magnetic. The most common magnetic metals are iron, steels with a high iron content, nickel and cobalt.

Metals as electrical conductors

Thinking about the learning

The classification of materials into electrical conductors and insulators in primary school suggests to children that metals are special when it comes to electricity. It is not therefore surprising that the same classification is transferred in children's thinking to the topic of magnetism. Metals are expected to be magnetic and non-metals are expected to be non-magnetic.

Gravity is not related to magnetism

Wrong Track: We are pulled down onto the Earth's surface by gravity. Gravity works because the Earth is like a giant magnet which attracts things to the surface.

Right Lines: Gravity is not related to magnetism.

Forces associated with the Earth

Thinking about the learning

This is a common conflation. Children know that magnets are associated with a magnetic force and that there is magnetism associated with the Earth. When a mechanism is sought to explain gravity, magnetism therefore becomes an obvious candidate.

The gravitational force and magnetic force are different in nature, as an example shows.

Imagine two magnets: the magnetic force between them will and two attracting and repelling (depending on the orientations), whilst the gravity force between them will always be attractive.

Now imagine two non-magnetic bars of identical mass to the magnets: there will be no magnetic force between them (whatever the orientation of the bars), but the gravity force between them will still always be attractive, and of the same value as before.

Magnets act-at-a-distance

Wrong Track: Magnets need air to work. If there's nothing between them they can't attract or repel each other.

Right Lines: The magnetic force requires no medium to act at a distance. Magnets will attract and repel just as well through a vacuum as in air.

Action at a distance

Thinking about the learning

Some pupils will argue that air is needed to enable magnets to attract and repel each other.

This line of argument is certainly incorrect, but it is also understandable in that it suggests a medium through which the magnets can act at a distance.

Thinking about the teaching

You might want to challenge this wrong track thinking directly in your teaching by setting up a demonstration. This might involve placing a piece of iron in a bell jar, removing all of the air from the jar with a vacuum pump and seeing whether the iron is still attracted to a powerful magnet held outside the jar. Ask for pupil predictions before you start removing the air.

The field idea

Wrong Track: The magnetic field is those iron filings around it.

Right Lines: The magnetic field is the space around the magnet where it will attract or repel other magnets.

Fields cannot be seen

Thinking about the learning

The very idea of a magnetic field is a demanding one to get hold of. The fact of the matter is that the magnetic field is a theoretical idea invented by physicists to allow us to describe the action of magnets as they attract and repel. It is possible to maintain that it is not anything real, there is nothing to see or touch around the magnet. When pupils first come across this idea of the magnetic field, it is not surprising that they sometimes go off down the wrong track in their thinking!

Thinking about the teaching

It is important to keep coming back to the essential idea that the magnetic field is the space around the magnet where it exerts a force. You might explore that space with iron filings and plotting compasses, but these simply tell us about the direction and strength of the force acting, they do not make the field any more real.

If you look in a science textbook at a magnetic field diagram for a bar magnet it will almost certainly show a 2D representation. It is worth emphasising however, that the magnetic field exists in the space all around the magnet – magnetic fields exist in 3D spaces.

Teacher Tip: Ask the pupils!

You might introduce the idea of magnetic fields, carefully making all of the key points set out above, but even then it is worth asking your pupils what they understand by the idea of magnetic field. Ask them to jot down a sentence or two. You might be surprised by what they write!

Spotting the pattern

Thinking about the teaching

Our experience over many years of directing pupils to scatter iron filings around bar magnets has shown that the magnetic field patterns which seem so clear to us are far from obvious to the vast majority of pupils. Indeed how else could it be? This is one of those situations where:

… if you know what you are looking for, it's obvious

… if you don't know what you are looking for, it's hopeless!

We have a physics teacher friend who remembers teaching a year 8 class about magnetic fields. The pupils were drawing the magnetic field pattern around a bar magnet, using iron filings, and our friend looked over the shoulder of one of the pupils. The boy was producing a drawing that was heavy with shading and, in some ways, captured what was in front of him, but that displayed nothing of the magnetic field pattern which the teacher actually wanted. The teacher pointed at the boy's drawing and then at the actual pattern of iron filings, and said:

Teacher: John, just look at the iron filings and look at your drawing! Does it look anything like that? Are you looking at the same thing as me?

As soon as he had said this, our teacher friend smiled to himself. The point could not have been more clear. The teacher and pupil were looking at different things. The teacher saw a magnetic field pattern, the pupil saw clumps of iron filings. Before the pupil could draw the field pattern he needed more instruction in what it was that he was looking out for.

There is an important message for teaching here.

Teacher Tip: Guide pupils as to what to see: don't expect what is obvious to you to be obvious to them.

Losing magnetism

Wrong Track: The magnet sends out electricity to make it attract and repel. That's why it loses its strength.

Right Lines: Magnets wear out as their internal mini-magnets become disordered, pointing in all directions.

Thinking about magnets wearing out

Thinking about the learning

In real life, permanent magnets do wear out and lose their magnetism. Pupils sometimes associate this with the magnet giving something out to make it attract and repel.

Thinking about the teaching

This idea of the magnet sending out electricity is incorrect, but the question as to why magnets wear out is a good one. It's best thought of in terms of the mini-magnet model introduced in the Physics Narrative.

A south pole in the Northern Hemisphere

Thinking about the teaching

The point was made in the Physics Narrative that the Earth's magnetic pole in the Northern Hemisphere is, in fact, a south pole. This follows directly from defining the end of a compass needle which points north as the north seeking pole.

This is not an important point in terms of developing your pupils' understanding of magnetism. Furthermore, it is not something which you need refer to since a compass needle is all you need to find the north and south poles of a magnet.

Nevertheless if a pupil does ask the question:

Jef: So does that mean the magnetic north is a south pole?

… you can reply with absolute confidence:

Teacher: What an excellent question! Yes it does!

There's a good chance you could improve your teaching if you were to:

Try these

• using an explicit model of permanent magnets
• being consistent in the drawing of force arrows
• giving children a variety of representations to hand when asking for descriptions
• explicitly modelling the drawing of magnetic fields
• explaining the interpretation of magnetic field diagrams – and why field diagrams are important
• speaking, acting and drawing with exemplary precision, so children can apprentice their practice on yours
• giving extensive first-hand, physical, experience of the forces between magnets
• explicitly modelling the replacement of an interaction with a force, by isolating one magnet from its environment
• exploiting the sensations of action-at-a-distance in your own hands
• explicitly introducing the purposes of the field idea at the same time as the idea
• moving from north-seeking pole to north pole
• using the mini-magnets representation to support predictions

Teacher Tip: Work through the Physics Narrative to find these lines of thinking worked out and then look in the Teaching Approaches for some examples of activities.

Avoid these

• relying too much on precise words by themselves
• acting as if the drawing of magnetic fields is obvious
• referring to gravitational, electrical and magnetic effects without taking great care to separate them
• linking the atmosphere to mediating either gravitational or magnetic forces
• assuming that action-at-a-distance is not problematic

Teacher Tip: These difficulties are distilled from: the research findings; the practice of well-connected teachers with expertise; issues intrinsic to representing the physics well.