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

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

     

7.1.2-Inducing-magnetism-in-a-magnetic-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.7.1.2-WE-Magnet-question-imageWhich 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?7.1.2-WE-Magnet-question-table

 

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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