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Magnetism Grade 12 Physics

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Magnetism Grade 12 Physics

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    1. Magnetism Grade 12 Physics Chelstone High School Mr. S. S. Simfukwe

    2. Properties of Magnets They attract ferromagnetic materials They have magnetic poles They obey the first law of magnetism

    3. Ferromagnetic materials These are metals which are attracted by magnets Examples include Iron, Cobalt, Nickel and alloys of these metals.

    4. Magnetic Poles These are areas on the magnet where magnetism is concentrated (mostly on the ends of the magnet). These poles are called North are South poles respectively.

    5. Law of magnetism It states that “Like Poles Repel and Unlike Poles Attract”.

    6. Test for Magnets Remember that unmagnetised iron, steel, cobalt and nickel objects will be attracted to either pole of a magnet. This means you can only show that an object is a magnet if it repels a known magnet. Therefore Repulsion is the best test for Magnetism.

    7. Magnetic Properties of Iron and Steel. Iron is easier to Magnetise and Demagnetise, therefore it is called soft iron. Steel is hard to Magnetise and Demagnetise, therefore it is called hard iron.

    8. Making Magnets Hammering with a steel bar in a North-South direction can make a magnet.

    9. Stroking a piece of unmagnetised iron or steel with a known magnet can make it into a magnet.

    10. Placing a magnet alongside a non-magnetised steel knitting needle for some time will magnetise it.

    11. An electric current has a magnetic effect. Winding a nail with a wire and then connecting the wire to a cell produces a magnet.

    12. This causes the molecules or dipoles to line up in the North-South orientation.

    13.  Demagnetizing A magnet can be destroyed by hammering. Heating a piece of magnetized iron or steel strongly in a flame will demagnetize it.

    14. Placing a magnet in a solenoid (coil of wire) carrying alternating current will also cause it to demagnetize.

    15. Magnetic Fields Magnetic field is the area around a magnet where its magnetic forces can be detected. The magnetic field can be seen by placing the magnet under a piece of paper with small iron filings on top.

    16. Magnetic Fields Two like poles will repel each other. These may be two North poles or two South poles, they will both have the same magnetic field shape. The region in the centre of the poles shown by the red star has no magnetic field,

    17. Magnetic Fields The poles of this free magnet are ATTRACTED to the OPPOSITE poles of the stationary' magnet.

    18. Uses of Magnets Electric Bell Motors Speakers etc

    19. Practice 1. State three properties of magnets? Attract ferromagnetic materials. They have magnetic poles. They obey the first law of magnetism.

    20. 2. List down three ways you can make a magnet Hammering in North-South direction. By using direct current. Stroking with a permanent magnet.

    21. 3. How can you demagnetize a magnet? Heating to hot-red Strongly hammering it. Placing it in a solenoid carrying alternating current.

    22. 4. Define magnetic field? This is the area around a magnet where its magnetic forces can be detected.

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