Edexcel IGCSE Physics 复习笔记 6.1.3 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

ANSWER:  A

• • 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.

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