Magnetism

Magnetism

1. The Earth's Magnetic Field

   • For hundreds of years people used compasses. They first used Magnetite (Lodestone)
   • The Earth's iron core creates a magnetic field. The North poles of magnets (eg. compass needles) are attracted to the geographical North Pole of the Earth.

2. Opposite poles attract, like poles repel

3. Domain theory

   • Iron, Steel, Cobalt and Nickel are magnetic materials
   • These materials are made of domains where the crystals point the same way
   • The domains all point in random directions, so have no overall magnetic field. But if stroked with a magnet, the domains realign to point the same way and the fields combine to make a magnet.
   • However, if heated or hit with a hammer, the domains realign to a random orientation

4. Field Lines

   • They show us which way a North Pole would feel the force of a magnet.
   • They always go away from the North pole, towards the south pole (arrows have to be drawn). No field lines should cross. Where the lines are closest together shows where the strongest force is felt.

5. Magnetic fields

6. The experiment

   • To investigate factors which effect the strengthe of an electromagnet. We changed the number of turns around the magnet and measured the strength by eeing how many paperclips it picked up.
   • We kept these the same: material of wire; thickness of wire; size of core; same size of paperclips; material of core.
   • The more turns, the more paperclips held so the stronger the electromagnet becomes. Eventually if you add enough turns the electromagnet reaches a maximum strength as al the domains have lined up

7. Uses of electromagnetism

   • scrap yards and recycling
     • An electromagnet is used to lift iron and steel. It is switched on to attract the materials and switched off to release them
     • In recycling centres, it is used to separate aluminium from iron and steel
   • A relay switch
     • A switch which allows us to turn on larger woltage appliances by first turning on smaller voltage. The small current passes through the coil of the relay and this magnetises it.
     • The armature is attracted towards the coil and touchesthe contact, therefore making another circuit complete.
   • A circuit breaker
     • It can be used instead of a fuse. It breaks the circuit if there is too much current flowing because of a malfunction or an overload.
     • The coil of the circuit breaker carries enough current so its magnetism is stron enough to attract the armature. The armature swings over, breaking the circuit and stays there until the circuit is fixed and the breaker can be reset.
   • Electric Bell
     • Button pressed. Current flows. Electromagnet operates. Attracth armature. Strikes gong. Circuit broken at screw. Electromagnet turns off. Cycle repeats for as long as the buttons is pressed.
   • Loud Speaker
     • It receives an alternating current which causes the electromagnet to alternate its polarity. The makes the coil pull in and out of the permanent magnet.
     • This vibrates the cone and produces cound. The cound varies in loudness and pitch depending on the signal it receives.

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