Topic 7 Magnetism

6.2 Properties of (permanent) magnets

• The ends of a magnet are called poles

• Magnets have two poles: a north and a south

• Opposite poles of a magnet attact(e.g. S and N)

• Like poles of a magnet repel (e.g. S and S or N and N)

• The attraction or repulsion between two magnetic poles occurs due to the magnetic force.

6.3 Magnetic Materials (magnetically hard & soft)

• Magnetically soft materials (e.g. iron):

  • Are easy to magnetise

  • Easily lose their magnetism, temporarily magnetised

• Magnetically hard materials (e.g. steel):

  • Are difficult to magnetise

  • Do not easily lose their magnetism, permanently magnetised

• Permanent magnets are made out of magnetically hard materials

• Electromagnets are made out of magnetically soft materials

  • This means that electromagnets can be made magnetic or non-magnetic as an when required： A steel pin will be attracted when an electromagnet switches on but not when it switches off. It is always attracted to a permanent magnet 

Magnetic field

• All magnets are surrounded by a magnetic field.

• A magnetic field is defined as: The region around a magnet where a force acts on another magnet or a magnetic material.

6.4 Magnetic field line

• Magnetic field lines (are visual, imaginary lines) used to represent the strength and direction of a magnetic field.

• direction: shown by arrows

• strength: shown by the spacing of the magnetic field lines

  • If lines are close together = the magnetic field will be strong

  • If lines are far apart = the magnetic field will be weak

• Magnetic field lines always go from north to south and are always parallel (never cross).

Non-magnetic and magnetic material

• Non-magnetic materials are materials that are not attracted to magnets and that cannot be magnetised.