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PHYSICS · Stage 8 · Chapter 8: Magnetism and Electromagnets

Physics 8.1 The properties of magnets — Magnetic Poles, Attraction, Repulsion and Magnetic Materials

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Physics 8.1 The properties of magnets — Magnetic Poles, Attraction, Repulsion and Magnetic Materials — Alhussan International Academy — Physics (Stages 7–9) notes: Describe the properties of magnets, know which materials are magnetic and use domains to explain magnetic behaviour.…

  • Non-contact force
  • North-seeking pole
  • Magnetic elements
  • Compounds and alloys
  • Steel and lodestone
  • Non-magnetic

Part 1 of 6Magnets and magnetic forces

  • Lodestone — The Ancient Greeks found that this naturally magnetic, iron-containing rock attracted small pieces of iron.
    • It was first found in Magnesia in Greece.
  • Non-contact force — A magnetic force acts even when objects are not touching.
  • Poles — Every magnet has a north pole and a south pole, and the forces are strongest at the poles.

Part 2 of 6Attraction and repulsion

Poles brought togetherForce
North and south (unlike)Attract
North and north (like)Repel
South and south (like)Repel
  • Compass — A freely suspended magnet turns to point north-south because the Earth behaves like a giant bar magnet.
  • North-seeking pole — The end that points north.

Part 3 of 6Magnetic materials

  • Magnetic materials = materials that are attracted to magnets.
  • Magnetic elements — Iron, cobalt and nickel are magnetic elements.
  • Compounds and alloys — Some of their alloys and oxides are also magnetic.
  • Steel and lodestone — Steel is magnetic because it is mainly iron, and lodestone (magnetite) contains iron oxide.
  • Non-magnetic — Copper, aluminium, brass, plastic, wood, glass and cotton are not magnetic.
  • Attraction only — A magnetic material is attracted to a magnet but is never repelled by it.
    • Magnetic materials do not attract or repel each other.
    • Only two magnets can repel each other, so repulsion is the test for a magnet.

Part 4 of 6Domains

  • Domains very small regions in a magnetic material, each behaving like a tiny bar magnet.
  • UnmagnetisedThe domains point in many different directions and their effects cancel.
  • MagnetisedThe domains line up when the material is put near a magnet or stroked with it.
  • Breaking a magnetEach piece is a magnet with its own north and south pole because the domains remain.

Part 5 of 6Magnetising and demagnetising

  • Iron — It is easy to magnetise but loses its magnetism when the magnet is removed.
  • Steel — It is harder to magnetise than iron but stays magnetised, making a permanent magnet.
  • Stroking — Stroking a steel needle repeatedly in the same direction with a magnet makes a stronger magnet.
  • Demagnetising — A permanent magnet cannot be turned off but can be demagnetised.
    • Heating it to a high temperature jolts the domains into random directions.
    • Hitting it with a hammer or dropping it does the same.

Part 6 of 6Everyday uses

  • Credit card stripA plastic containing tiny iron pieces that behave like magnets stores information.
  • Other usesFridge door seals, compasses, loudspeakers, motors and magnetic catches.
  • Magnetic levitationThis happens when like poles repel.
TestResult for a magnetResult for unmagnetised iron
Near one pole of a known magnetAttracts or repelsAttracts only

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