1. Describe the properties of magnets.
● opposite poles attract; same poles repel
● field lines travel from N to S
● produces a magnetic field which can then produce a current
● a temporary magnet that loses its magnetism easily is known as a soft magnet
● a permanent magnet that does not lose its magnetism easily is known as a hard magnet
2. Give an account of induced magnetism.
When you rub a wire between a N and S pole, the wire cuts the horizontal magnetic fields at a 90° angle. This induces a current.
The same thing occurs with a solenoid (a coil of wire) and a magnet. The magnet is moved inside the solenoid, creating a current.
The speed of the magnet within the solenoid and the amount of coils of the solenoid both affect the current induced. Faster movement and more coils induce a greater current.
3. Identify the pattern of field lines round a bar magnet.
This diagram basically sums up this point on the syllabus.
4. Distinguish between the magnetic properties of iron and steel.
| Iron | Steel |
|---|---|
| Is a soft magnet | Is a hard magnet |
| Useful for making temporary electromagnets; strong but temporary | Slow to magnetise but retains its magnetism |
| High susceptibility, low retentivity | Low susceptibility, high retentivity |
5. Distinguish between the design and use of permanent magnets and electromagnets.
Permanent magnets
● magnetism is permanent
● its atoms are aligned to produce a constant magnetic field
● used for compasses, fridge magnets, and cabinet doors
Electromagnets
● magnetism works only when a current is induced
● used for transformers, motors, and loudspeakers
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