1. Magnets

2. History of Magnetism
The Chinese discovered the magnetic compass as early as 200 BC. At first fortune-tellers used it. Later people realised that it was a way to find the direction of North and South.

3. History of Magnetism
The ancient Greeks knew that the lodestone or magnetite attracted iron towards it. It is known that the Vikings used a lodestone to navigate. Later at the end of the twelfth century Europeans were using this simple compass to aid navigation.

4. History of Magnetism
During the 16th century Sir William Gilbert discovered that the properties of the lodestone could be transferred to ordinary pieces of iron by rubbing them with a lodestone.

5. What is a Magnet
The first magnets were made of iron. These days they are can be made from:
iron
nickel
copper
cobalt
aluminum .

6. What do Magnets do? They attract certain materials: iron steel nickel
cobalt

7. What do Magnets do?
Magnetic materials are attracted to the poles of the magnet.
On a bar magnet the poles are at either end of the magnet.
Poles occur in pairs of equal strength.
One pole - North - N pole- pointing roughly to the Earth's North pole.
Other pole - South - S pole

8. What do Magnets do? Like poles repel Unlike poles attract
Force between magnetic poles decreases as their separation increases.
An unmagnetized magnet material would be attracted to both poles.

9. Magnetic Field
A magnetic field is the area around a magnet in which a force is experienced.

10. Magnetic Field of a “U” Magnet

11. Like Poles have Fields that Repel

12. Unlike Poles have Field that attract

13. The Earth has a magnetic Field

14. Theory of Magnetism
If a magnetic piece of steel rod is cut into smaller pieces, each piece is a magnet with a N or a S pole.
Therefore a magnet can be said to be made of lots of "tiny" molecular-sized magnets all lined up with their N poles pointing in the same direction.

15. Magnetic Theory

16. If you split a magnet in half?

17. If you split a magnet in half?

18. If you split a magnet in half?

19. Can Magnet Be Destroyed?
hammering a magnet
heating
dropping a magnet
demagnetizing by using reduced alternating current through a coil of wire wrapped round a magnet

20. Can a Magnet be made?
When a piece of unmagnetised magnetic material touches or is brought near to the pole of a permanent magnet, it becomes a magnet itself.
The magnetism is induced.

21. Electromagnets
A coil of wire with electricity flowing through it acts as a bar magnet.

22. Electromagnet
Placing a piece of iron into the coil induces a magnetic effect in the iron when the current is flowing in the coil and so turning it into an electro-magnet
you can turn the magnet on and off by using a switch to turn the current and off.

23. Increasing the strength of Electromagnets
increasing number of coils
increasing the current
using an iron core (iron magnetizes and demagnetizes quickly, whereas steel takes time to magnetize and demagnetize)

24. Use of Electromagnets Electric generators Electric Motors Loudspeakers
Telephones
Tapes - flexible magnets