Where is the electric current?
Teaching Guidance for 11-14
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.