1. MAGNETISM

2. The Earth itself has a huge magnetic field - as if it had a huge bar magnet embedded at its centre. The Earth’s magnetic field lines emerge from near the geographical north pole and re-enter it at the south pole. The nature of the field around the Earth varies in both strength and direction. The Earth’s magnetic field is strongest at the magnetic poles and weakest near the Equator. The field also varies with time, for example, the poles are known to wander as shown in the bottom picture and sometimes the polarity reverses completely!

3. The metals affected by magnetism consist of tiny regions called 'Domains' which behave like tiny magnets. Normally they are arranged in the magnetic material all pointing in different directions in a completely random fashion and so their magnetic effects cancel each other out. If an object is magnetised it is because the domains are all made to point in the same direction. This can be done by stroking the magnetic material with a magnet (or magnets) as shown in the diagram. When aligned the domains reinforce one another and create north and south poles at either end.

4. Field lines run from North to South.
The magnetic field is strongest at the poles.

5. Unlike poles attract.
North and South.
Like poles repel.
North and north.
South and south

6. MAGNETIC FIELD PATTERNS
This diagram shows the magnetic field patterns around the unlike and like poles of a pair of magnets. Note that magnetic field lines never cross. The strength of the magnetic field is proportional to the space between the field lines. The poles, where the field is strongest, is also where the field lines are closest together.

7. Like poles are repelling so the magnet on the right is suspended in the air.

8. Investigation:
You are given two magnets find out which one is strongest

9. SOME MAGNET FACTS
The poles of Earth can change. Magnetic lines of rocks laid down long ago show that once the North pole was the South pole; and the South pole the North pole
Your favourite music and television programmes can be stored magnetically. Sound and video tapes are plastic ribbons with a magnetic coat. Information is recorded on the tapes as magnetic fields. Stroke them with a magnet and all this information which includes sound and pictures will be lost forever
A letter written in 1269 by the Scientist calling himself Peter the Pilgrim has the first mention of the poles of a magnet
An Alnico magnet is a combination of aluminium, nickel and cobalt, and can be very powerful.
The strongest magnets are ceramic. They are made from metal powders, heated together under very high pressure

10. Things that will make a magnet stronger
The bigger horseshoe magnet will be strongest and the larger bar magnet will also be stronger. (The bigger the magnet the stronger it will be.) There are more domains which can become magnetised and they all contribute to the total magnetic effect.

11. The horseshoe magnet will be stronger because it is folded so it is bigger, also both poles are closer together and the poles are the strongest part of a magnet, having them closer will increase the magnetic field.
They will be the same because even when you straighten the horseshoe magnet the bar magnet is thicker. – More domains – I.e. it has more metal.
Short and fat will be stronger than long and thin more domains near the poles creating a strong magnetic effect at the poles.
The plastic cover will weaken the magnetic field

12. Plan of the Investigation
Suspend two magnets using sellotape
Add paperclips in a long chain and see which chain is longest.

13. Fair Testing The same size paper clip
Same place – not near another magnetic field , or near another metal object.
Same temperature
Same pole of magnet.
Paper clips of the same metal – must not be magnetised before, not joined together.

14. What I will measure.
The number of paper clips in a row.

15. Results and conclusions

16. What My graph shows
The larger the magnet the greater the magnetic strength.
The magnetic field is increased because if there are more domains exerting a magnetic field the combined strength will be greater.
The large magnet held 23 more pins than the smallest magnet and 11 more than the medium magnet.

17. Summary of Magnetism
Only iron, steel,nickel and cobalt are magnetic.
Bar magnets have to be made using one of these substances.
All bar magnets have invisible magnetic fields.
One end of a magnet is called the north pole – this is the side which will swing to face the Earths’ magnetic north.
The field lines always point from the North pole to the South pole.

18. Magnetic fields
Magnetic fields are regions where they experience a magnetic force.
You can investigate these using a plotting compass or iron filings.
Like poles repel and unlike poles attract.

19. A wire with a current in it has a magnetic field around it.
Electromagnets
A wire with a current in it has a magnetic field around it.
The strength of a magnetic field can be increased in three ways:
Increase the amount of current flowing
Increase the number of coils
A larger soft iron core.
A reed relay is an electromagnetic switch.

20. An electromagnet A soft iron rod has no magnetic field
When current flows in the wire the soft iron becomes magnetised so a magnetic field is detected by the plotting compasses.

21. The first electromagnet was made by an English scientist called William Sturgeon in It could lift a few pins. Modern electromagnets can lift whole cars. Some are so powerful they affect metals, like copper, which are not usually magnetic.

22. A small current in one circuit is used to switch on a much larger current in another circuit.
When the small current is switched on the electromagnet A activates and the iron lever is attracted to it. This causes the arm to move which closes the contact B in the other circuit.
The circuit is complete so the current then flows.
Reed relay

23. An electric bell also uses an electromagnet
An electric bell also uses an electromagnet. See if you can describe in your own words how the bell works.

24. Your Answer should be like this:
A The bell push is closed which allows a current to flow.
B The electromagnet becomes magnetized and the armature is pulled to the magnet this makes the hammer hits the gong.
As this happens the contact is broken so it not a complete circuit so the electromagnet is de-magnetized.
C The armature is no longer attracted so it jumps back.
This closes the contact, so electricity flows again and the armature is once more attracted to the electromagnet.The whole cycle is repeated until you stop pressing the bell push.