Bringing together two sets of constraints

Focusing on the learners:

Distinguishing–eliciting–connecting. How to:

• account for the action of devices using simple ideas

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:

• relate the actions of electromagnets to the actions of permanent magnets
• keep electrical and magnetic loops separate

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.

It's all magnetism

Wrong Track: Bar magnets are different to electromagnets, it's a different kind of magnetism.

Right Lines: Permanent magnets and electromagnets give rise to the exactly same kind of magnetic force.

Making the connection

Thinking about the learning

An electromagnet certainly looks quite different to a permanent bar magnet. It is therefore understandable that learners might believe that the two sources produce quite different kinds of magnetism.

Thinking about the teaching

When moving on from permanent magnets to electromagnets it is worth emphasising the point that you are exploring a new way of producing the same kind of magnetic effect. Avoid giving the impression that you are starting a brand new topic.

Where is the current?

Wrong Track: When you switch on the power supply for the electromagnet there is an electric current that flows through the coil of wire and into the iron. The electric current then turns the iron core into a magnet.

Right Lines: The electric current in the coils of wire of the solenoid creates a magnetic field, magnetising the iron core. There is no current in the iron core.

Current doesn't flow through the core

Thinking about the learning

When making an electromagnet in class, pupils are likely to wrap a coil of insulated wire around a nail or some other piece of iron. Pupils often assume that when the circuit is switched on the electric current flows from the wire and into the nail (despite the wire being insulated). This is not the case. The electric current remains in the wires wrapped around the nail. It is the magnetic field due to the electric current that affects the nail.

Thinking about the teaching

The magnetic loop and the electrical loop are quite separate. There is more on this in the SPT: Electricity and energy topic, where electromagnetic devices are discussed in more detail.

Adding to electromagnets

Thinking about the learning

The idea that an electromagnet can be made stronger by…

• Increasing the number of coils (or turns) of wire
• Increasing the electric current through the coil
• Placing a magnetic material inside the solenoid coil

… is one which makes sense to most pupils.

Some may ask:

Lorna: Why is it that adding the iron core increases the strength of the electromagnet?

The simple idea here is that the iron becomes magnetised so that now, not only do we have the magnetic field due to the electric current passing through the coils of wire, but also the additional field due to the magnetised iron.

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

Try these

• relate the actions of electromagnets to those of permanent magnets
• be very clear to separate electrical loops from magnetic fields
• construct careful step-by-step accounts of the action of devices

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

• conflating the field with the coil producing the field

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.