S4.13.2 For the adult
Fields around wires and coils
A plain copper wire is not a magnet. Yet a wire from a cell can make a compass needle turn. How?
What this chapter teaches
A current in a wire makes a magnetic field in circles round it. The right hand grip rule gives its direction: thumb along the current, fingers round the field. A coil adds the fields of its turns into a strong, even field inside, like a bar magnet. More turns, more current and a soft iron core make it stronger.
Three questions to ask
There is no one right wording. Listen for the idea.
- Which way does the field go round a wire when the current comes out of the page towards you?
- Why is the field inside a long coil strong, and how can you make it stronger?
- How could you use a compass to show that a wire with a current has a magnetic field?
After the chapter, the learner can
- Use the right hand grip rule to find the direction of a field
- Explain how a coil of wire makes a strong, even field
What they copy into their notebook
A current has a field in circles round the wire. Right hand grip: thumb with the current, fingers with the field. A coil adds its turns: strong and even inside. More turns, more current, soft iron core.