Magnets

Magnets

1. Types of Magnets

   • Natural: Lodestone
   • Man-made: Button, Ring, Bar, U-shaped and Horseshoe

2. Magnetism

   • the pull force of a magnet
     • strength is uneven and strongest at its ends
     • can penetrate some thin non-magnetic materials (paper, glass, etc)
   • Magnetic and Non-magnetic Materials
     • Magnetic Materials
       • can be attracted to magnet
       • usually made from metals like iron, steel, cobalt and nickel
       • can be used to make magnets
     • Non-magnetic Materials
       • cannot be attracted to magnet
       • usually made from materials with no magnetic force like glass, wood, plastic etc
       • cannot be made into magnets
       • allow magnetic force to pass through

3. Magnets' Properties

   • 2 poles at the ends: North and South poles
   • like poles repel (push away) while unlike poles attract (pull closer)
   • freely suspended magnet will rest in North-South direction
   • only magnets and magnets can repel each other
   • can make another object magnetic
   • strength of magnets does not depend on its sizes or shapes
   • the further the distance between the magnet and object, the stronger the magnetic force

4. Making Magnets

   • stroking: must be stroked in one and same direction many times
   • electricity: will become an electromagnet , the more wire coils around the object and more batteries will make the magnetic force stronger
   • induction: object touch magnet and become magnetised

5. Demagnetising Magnets

   • dropped it many times
   • hit with a hammer repeatedly
   • heat it over fire

6. Storage of Magnets

   • using a keeper, a soft iron bar used to join the magnetic poles

7. Uses

   • to keep doors close in refrigerators
   • televisions
   • compass to tell directions
   • separating and sorting magnetic materials from non-magnetic materials in scrap car yard