1. 18 June, 2018 Magnetic fields

2. Magnetic materials cobalt (Co) gold (Au) iron (Fe) nickel (Ni)
Which of the metals below are magnetic metals?
cobalt (Co)
gold (Au)
iron (Fe)
nickel (Ni)
copper (Cu)
zinc (Zn)
magnesium (Mg)
aluminium (Al)
silver (Ag)

3. Magnetic materials S N Ni Fe Co Au Mg Cu Zn Al Ag
A magnetic material is attracted to a magnet.
Only iron (Fe), nickel (Ni) and cobalt (Co) are magnetic. N S Fe Ni Co Al Zn Ag Cu Au Mg

4. Magnets
Attract or repel other magnets. Also attract magnetic materials.
Magnetic materials
Attracted to magnets but do not attract or repel each other
Non-magnetic materials
Not attracted to magnets

5. Forces between magnets – experiment

6. What is a magnetic field?
The region around a magnet where it has a magnetic effect is called its magnetic field.
When a magnetic material is placed in a magnetic field it will experience a force. S N
The iron filings feel the effect of the magnetic field and show the direction of the forces in this region.

7. Shape of a magnetic field
What is the shape and direction of the lines of force in the magnetic field around a bar magnet?
strongest field
at poles
strongest field
at poles N S
weakest field further away from poles
Where is the magnetic field strongest?

8. Viewing magnetic fields: N poles together
Bring the north poles of two bar magnets together.
What happens to the magnets? S N N S
Next, bring the two north poles as close to each other as possible and place a piece of paper on top of the magnets.
Use the plotting compass to draw the field.

9. Magnetic field pattern: N poles together
What do you notice about the pattern of the lines of force in the region between the two north poles? S N N S

10. Viewing magnetic fields: N and S poles together
Bring the north and south poles of two bar magnets together.
What happens to the magnets? S N S N
Next, put the north and south poles close to each other, without letting them touch, and place a piece of paper on top.
Use the plotting compass to draw the field.

11. Magnetic field pattern: N and S poles together
What do you notice about the pattern of the lines of force in the region between the north and south poles? S N S N
How does this pattern compare with the pattern between the two north poles?

12. Magnetic fields – summary
1. When two like poles (e.g. two north poles or two south poles) are put together, they repel each other.
2. When two unlike poles (e.g. a north and a south pole) are put together, they attract each other.
3. Scattering iron filings around a bar magnet or using a plotting compass makes it possible to see the lines of force of the magnetic field.

13. There are three methods that can be used to make a magnet:
Making a magnet
A magnet can be made by magnetizing a material which is attracted to a magnet, e.g. a paper clip.
There are three methods that can be used to make a magnet:
Stroke a magnet along the paperclip from one end to the other and then starting from the same place, repeat the movement. The more times this is done, the more magnetic the clip becomes.
Hold a nail in a magnetic field and hit it with a hammer.
Put a magnetic material in a strong magnetic field.

14. The Earth’s core contains a lot of molten iron that scientists believe is responsible for the Earth’s magnetic field.

15. 18 June, 2018
Electromagnets

16. Making an electromagnet
When electricity is passed through a coil of wire, the coil has a magnetic field around it. This is called an electromagnet.
If the coil of wire is wrapped around a piece of iron, such as an iron nail, the magnetic field gets stronger.

17. Investigating an electromagnet
An iron core at the centre of a coil of wire increases the strength of an electromagnet.
Two experiments can be carried out to investigate the other factors that can affect the strength of an electromagnet:
1. Investigate how the number of coils affects the number of paper clips attracted to an electromagnet – keep the current the same in this experiment.
2. Investigate how the size of the current affects the number of paper clips attracted to an electromagnet – keep the number of coils the same in this experiment.

18. Investigating an electromagnet – results 18 18 31 46

19. Investigating an electromagnet – results 212 23 38 49 60

20. Investigating an electromagnet – graph 1
number of clips attracted
number of coils

21. Investigating an electromagnet – graph 2
number of clips attracted
current (A)

22. Uses of Electromagnets
18 June, 2018
Uses of Electromagnets

23. Using electromagnets – scrap yards
A large electromagnet is used in a scrap yard to pick up and move heavy pieces of scrap metal.
Which metals would the electromagnet attract?
What advantages does an electromagnet have over a permanent magnet?

24. Using electromagnets – door bells
The circuit for a door bell includes an electromagnet.

25. Using electromagnets – relay
Lifts, cars and other large electrical machines use high currents.
A relay, which includes an electromagnet, is used to allow a small current in one circuit to control a large current in another circuit.

26. The Maglev Track
The underside of the train has large permanent magnets.
The track is also magnetised with the same pole so the train is repelled and floats.
The track also contains electromagnets which push the train along.

27. HWK: Revise for a test on static, electronics and electromagnetism.

28. Label the diagram – electric bell

29. Label the diagram - relay

30. Electromagnets – summary
1. When electricity is passed through a coil of wire, the coil behaves like a magnet and has a magnetic field around it
– this is an electromagnet.
2. There are three ways to make an electromagnet stronger:
wrap the coil of wire around an iron core;
increase the number of coils;
increase the size of the current.
3. An electromagnet can be easily turned on and off. This is why electromagnets can be used in scrapyards and as switches in electrical devices.