Section 1 of 4Making an Electromagnet
1
A current flowing in a wire creates a magnetic field around it, which is weak for a single straight wire.
2
Winding the wire into a coil concentrates the field, because the fields from each turn add together inside the coil.
3
Placing a soft iron core in the coil makes the iron into an induced magnet, so the combined field is much stronger.
4
The electromagnet is magnetic only while current flows, and it loses most of its magnetism when the current stops.
5
Reversing the current reverses the poles, while the field pattern remains like that of a bar magnet.
Section 2 of 4Increasing the Strength
Larger current
- A bigger current in the coil produces a stronger magnetic field.
More turns
- Adding more turns of wire to the coil increases the field, because more current loops contribute.
Iron core
- A core of soft iron greatly strengthens the field, because the iron becomes magnetised by the coil.
Wording
- Say "more turns on the coil" rather than "more coils", since the coil is the whole object.
Section 3 of 4Why Soft Iron
Why Soft Iron
Easily magnetised
- Soft iron becomes magnetised quickly when current flows through the coil.
Easily demagnetised
- It loses its magnetism when the current is switched off, so objects can be released.
Steel core
- Steel is magnetically hard and would stay magnetised, so it is unsuitable for an electromagnet that must switch off.
Uses
- Electromagnets lift scrap metal in scrapyards and are used in relays, electric bells and locks.
| Feature | Permanent magnet | Electromagnet |
|---|---|---|
| Always magnetic | Yes | No, only with current |
| Strength adjustable | No | Yes, by changing current or turns |
| Poles reversible | No | Yes, by reversing current |
| Core material | Magnetically hard (steel) | Magnetically soft (iron) |
Section 4 of 4Exam Checklist & Tips
3.1.8 – Key Points for the Exam
- Electromagnet A coil of wire wound on an iron core that is magnetic only while current flows.
- Solenoid A long coil of wire that produces a magnetic field like a bar magnet when a current flows.
- Soft magnetic material A material such as iron that is easy to magnetise and demagnetise.
- Core The iron placed inside a coil to strengthen its magnetic field.
- Relay A switch operated by an electromagnet.
Common Mistakes
- Writing "add more coils" instead of "add more turns to the coil".
- Suggesting steel as the core because it is stronger; it would stay magnetised.
- Saying an electromagnet is always magnetic.
- Forgetting that reversing the current reverses the poles but does not change the strength.