P4.1 Simple phenomena of magnetism

Describe the force between magnetic poles

• Opposite poles (N and S) attract

• Like poles (N and N or S and S) repel

What is a magnetic field?

• A region of space where another magnet or magnetic material experiences a force

  • All magnets are surrounded by magnetic fields

Draw a magnetic field diagram

Describe induced magnetism

• Magnetic materials only attract to each other if theres a permanent magnet present

• Once a permanent magnet attracts a magnetic material, it induces a magnetic field in the material

• This is called induced magnetism

How do you induce magnetism in a material?

• Stroking them with a magnet in one direction

• Using a d.c coil

• Hammering in a magnetic field (in north → south orientation)

How do you demagnetise a material?

• Hammering or heating: causes particles to unalign and lose magnetic properties

• Use of an a.c coil: causes domains to point in different directions

What is the difference between a magnetic and non-magnetic material?

• Magnetic materials:

  • Strongly attracted to magnets

  • Can be magnetized to form permanent magnets

  • Have magnetic domains which are aligned with an external field

• Non-magnetic materials:

  • No attraction or weak repulsion to magnets

  • Cannot be magnetized

  • Do not have magnetic domains at all

What are the properties of a temporary magnet and some examples?

• Easy to magnetise and unmagnetise

  • Soft magnetic materials:

    • Iron

    • Cobalt

    • Nickel

    • Mumetal

What are the properties of a permanent magnet and some examples?

• Difficult to magnetise and unmagnetise

• Hard magnetic materials:

  • Steel

  • Alcomax

  • Magnadur

What is an electromagnet?

• Magnet whose magnetic field is produced by an electric current flowing through a coil

  • Only creates magnetic field when current passes through it

State differences between electromagnets and permanent magnets

Permanent magnet	Electromagnet
Constant magnetic field	Temporary magnetic field which can vary in strength by adjusting the current
Cannot be switched on or off	Can be switched on and off quickly
North and south poles cannot be swapped	North and south poles can be changed by switching direction of current flow