Magnetic fields due to currents
| English | Chinese | Pinyin |
|---|---|---|
| electromagnet | 电磁铁 | diàn cí tiě |
| right-hand grip rule | 右手定则 | yòu shǒu dìng zé |
| solenoid | 螺线管 | luó xiàn guǎn |
| bar magnet | 条形磁铁 | tiáo xíng cí tiě |
| iron core | 铁芯 | tiě xīn |
A magnet you can switch off
- Coil some wire, switch on a current, and you have an electromagnet 电磁铁.
- Switch it off and the magnetism vanishes.
- Currents make magnetic fields — and we can predict their shape.
Current field rule lab
Connect current direction to the circular magnetic field around a wire.
Field around a straight wire
- The field forms circles around the wire.
- Find the direction with the right-hand grip rule 右手定则: thumb along the current, fingers curl the way the field points.
A metal plate swinging between magnet poles is rapidly slowed as induced eddy currents oppose its motion
The magnetic field around a long straight wire forms:
Concentric circles, with the direction given by the right-hand grip rule.
The right-hand grip rule gives the direction of the field around a current-carrying wire.
Thumb along the current, curled fingers show the way the circular field points.
Coils and solenoids 螺线管
- A flat coil acts like a small bar magnet 条形磁铁.
- Inside a long solenoid the field is nearly uniform; an iron core 铁芯 boosts it (used in electromagnets and transformers).
Iron filings trace the field lines around bar magnets
Inside a long solenoid the magnetic field is nearly ____.
Like a stretched bar magnet — the field inside is uniform and parallel to the axis.
Adding an iron core greatly increases a solenoid's magnetic field.
The iron's atomic magnets line up and add to the field — used in electromagnets and transformers.
Two parallel currents
- Each wire sits in the other's field. Using the left-hand rule:
- same direction → attract; opposite directions → repel. (This defines the ampere.)
A solenoid's field is nearly uniform inside and spreads out at the ends like a bar magnet; N and S poles are marked
Two parallel wires carrying currents in the same direction:
Same-direction currents attract; opposite-direction currents repel. This is the basis of the ampere.
You've got it
- a straight wire makes circular field lines — right-hand grip rule
- a solenoid's field is uniform inside; an iron core strengthens it
- parallel currents: same way attract, opposite ways repel