# Edexcel IGCSE Physics: Double Science 复习笔记：6.1.3 Permanent & Induced Magnets

### Permanent & Induced Magnets

Magnetic materials are attracted to a magnet; non-magnetic materials are not

• Very few metals in the Periodic Table are magnetic. These include:
• Iron
• Cobalt
• Nickel

• Steel is an alloy which contains iron, so it is also magnetic
• Magnetic materials (which are not magnets) will always be attracted to the magnet, regardless of which pole is held close to it

Magnetic materials attracted to magnets

• To test whether a material is a magnet it should be brought close to a known magnet
• If it can be repelled by the known magnet then the material itself is a magnet
• If it can only be attracted and not repelled then it is a magnetic material

• There are two types of magnets
• Permanent magnets
• Induced magnets

#### Permanent Magnets

• Permanent magnets are made out of permanent magnetic materials, for example steel
• A permanent magnet will produce its own magnetic field
• It will not lose its magnetism

#### Induced Magnets

• When a magnetic material is placed in a magnetic field, the material can temporarily be turned into a magnet.
• This is called induced magnetism

• When magnetism is induced on a material:
• One end of the material will become a north pole
• The other end will become a south pole

• Magnetic materials will always be attracted to a permanent magnet
• This means that the end of the material closest to the magnet will have the opposite pole to magnets pole closest to the material

Inducing magnetism in a magnetic material

• When the magnetic material is removed from the magnetic field it will lose most/all of its magnetism quickly

#### Worked Example

The diagram below shows a magnet held close to a piece of metal that is suspended by a light cotton thread. The piece of metal is attracted towards the magnet.Which of the following rows in the table gives the correct type of pole at X and the correct material of the suspended piece of metal?

• X must be a north pole
• The piece of metal is being attracted towards the magnet
• The law of magnetism states that opposite poles attract

• The material of the suspended piece of metal is nickel
• Nickel is a magnetic material (It will experience a force when it is placed in a magnetic field, in this case it is attracted towards the magnet)

• B is incorrect because X cannot also be a south pole (and hence is a north pole)
• If the pole at X was a south pole then the piece of metal would be repelled from the magnet because the law of magnetism states that like poles repel

• C and D are incorrect because aluminium is not a magnetic material
• A non-magnetic material would be unaffected by the magnetic field produced by the magnet.