1. Magnets
D. Crowley, 2008

2. Magnets
Thursday, April 13, 2017Thursday, April 13, 2017
To be able to draw field lines around a magnet, and to understand what these show

3. Magnets What do you know about magnets? What materials are magnetic?
What are poles?
What are magnetic fields?

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

5. Magnetic
A magnetic material is attracted to a magnet – only iron (Fe), nickel (Ni), and cobalt (Co) are magnetic: bar magnets have to be made from one of these N S Fe Ni Co

6. Magnets
Bar magnets are permanent magnets - their magnetism is there all the time and cannot be turned on or off
They have 2 poles: -
North pole (short for north-seeking pole)
South pole (short for south-seeking pole)
The North pole is normally shown as N and the South pole is normally shown as S

7. Magnets
Bar magnets have an invisible magnetic field around them – one end is the North pole and the other is the South pole
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
The iron filings feel the effect of the magnetic field and show the direction of the forces in this region N S

8. Iron Filings
We cannot see magnetic fields, however we can detect them using iron filings - the tiny pieces of iron line up in the magnetic field
Using the iron filings work out the shape and direction of the lines of force in the magnetic field around a bar magnet and say where the magnetic field is strongest…
Place a magnet down on the table
Lay a piece of paper over the magnet
Scatter the iron filings onto the paper
Draw the pattern the iron filings have made

9. Weakest fields furthest from poles
Iron Filings
The iron filings show that the magnetic field is strongest at the poles, getting weaker as you travel further from the pole
Strongest field at poles
Strongest field at poles
Weakest fields furthest from poles

10. Field Lines
The magnetic field line patterns show the relative strength of the magnetic fields (field lines always point from the North pole to the South pole)
The field lines come out of North pole and go into the South pole
The field lines are more concentrated at the poles
The magnetic field is strongest at the poles, where the field lines are most concentrated

11. North & South Poles
Iron filings can show the magnetic field between two magnets: -
This can show where unlike poles face each other, and so attract
This can show where like poles face each other, and so repel
Using the iron filings see how the magnetic fields vary between magnets where like poles and unlike poles face each other…
Bring the North / South poles of 2 magnets together, without letting them touch
Place a piece of paper on top, and scatter iron filings over the paper
Draw out the pattern
Repeat this bringing the North / North poles of 2 magnets together, without letting them touch

12. Attraction
Iron filings can show the magnetic field between two magnets where unlike poles face each other, and so attract
If we look at the field lines, we see that they go from the North pole of one magnet to the South pole of the other magnet

13. Repulsion
Iron filings can also show the magnetic field between two magnets where like poles face each other, and so repel
If we look at the field lines, we see that they do not go from one magnet to the other, and they do not cross

14. Attracted / Repelled

15. Forces
If you bring two bar magnets together, there are two things that can happen: -
If you bring a North pole and a South pole together, they attract and the magnets may stick together;
If you bring two North poles together, or two south poles together, they repel and the magnets push each other away
Unlike poles attract, and like poles repel

16. Making Magnets
A magnet can be made by magnetising 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