1. In This Section We Will Be Studying These Topics:
MAGNETS & MAGNETISM
In This Section We Will Be Studying These Topics:
What is a magnet?
How magnets can be made and destroyed.
Magnetic Fields and their effects.
Electromagnetism.
Factors affecting electromagnetism.
Uses of Electromagnetism.

2. Here are some everyday objects that use magnets.
Magnets of various types are important in our everyday life, even though we do not realise that they are there.
Here are some everyday objects that use magnets.
Washing machines.
Loudspeakers.
Microphones.
Computer floppy drives.
Electric bells.
Video players.

3. MAGNETS
Magnets are usually made of iron although they can be made of other materials. There is even a rock called lodestone that is magnetic. This is because it contains a lot of iron.
Iron is not normally magnetic.
Let’s have a look at why it becomes magnetic.
We can think of iron as containing lots of very tiny magnets. In normal iron these magnets are pointing randomly in different directions. So their magnetism is lost.
Ordinary iron.

4. MAGNETS
Magnetic iron.
In iron that is magnetic, all those tiny magnets have been organised so that they all point in the same direction. This means that their magnetic effect adds up and gives the iron magnetism.

5. MAGNETS
The most common type of magnet is a bar magnet. The strongest magnetic force is at the ends of a bar magnet. The ends are called the poles. N S
One end is called the North Pole.
The other end is called the South Pole.
Sometimes labelled N & S.
No matter what their shape all magnets have a north and south pole. The horseshoe magnet, often seen in cartoons, can be thought of as a bar magnet that has been bent. N S

6. Why do you think hammering or heating destroys a magnet?
MAGNETS
If you could break a magnet in half you would have two magnets each with a north and south pole. S N N S
A magnet can be made by stroking a piece of iron or other magnetic material in a circular motion. N S
This organises the tiny magnets in the material.
Why do you think hammering or heating destroys a magnet?
The magnetic effect can be destroyed by hammering or heating a magnet.
It disorganises the tiny magnetic poles that had lined up.

7. MAGNETS
If you place two magnets close together they will either attract each other and stick together, or push (repel) each other away.
The rule is: Like poles Repel e.g. N to N
Unlike poles Attract e.g. N to S.
What will happen to these? N S N S
Repel N S
Attract N S
Attract N S
Repel

8. MAGNETS
The strength of the attraction or repulsion between the magnets depends on their distance apart.
The force is strong in this one! N S
When the magnets are far apart, the force is weak. N S
As the magnets come closer the force gets stronger.

9. A magnet will attract the object made of magnetic material.
MAGNETS
How can we tell the difference between a magnet and an object made of magnetic material?
A magnet will attract the object made of magnetic material. N S
We cannot tell which is the north or south pole because both of the poles will attract the object.
If the objects repelled each other it must mean that they are two magnets. This is because they both must have magnetic poles that are the same.
In fact nearly all metals are not magnetic.
Can you find out which other materials are attracted to magnets besides iron?
Steel, cobalt & nickel.

10. MAGNETIC FIELDS
A magnet exerts a force all around itself not just at the poles.
This effect is called a magnetic field.
Although a magnetic field is invisible we can show it using iron filings. If a piece of card is placed over a magnet and then iron filings are sprinkled on the card the magnetic field will make the filings move into a pattern.
Another way we can show a magnetic field is by using a compass.
A compass has a needle which is really a very small bar magnet balanced on a pin or pivot so that it is allowed to rotate.
The needle lines up with a magnetic field.
Needle.
Pin or pivot.

11. MAGNETIC FIELDS
Another way we can show a magnetic field is by using a plotting compass.
A plotting compass is a small compass used to detect the magnetic fields of magnets.
If you place it around the magnet it will ‘line up’ with the magnetic field.

12. MAGNETIC FIELDS Put the magnet on a piece of paper.
The compass is moved so the rear of the needle is over the first mark and another mark is made at the needle point.
Place the plotting compass against the magnet and put a mark on the paper at the compass needle point. N S
Continue moving the compass and marking until a magnetic field line has been marked.
Then join the marks up with a line.
Repeat this process to draw as many field lines as possible.

13. The complete magnetic field of a bar magnet looks like this:
MAGNETIC FIELDS
The complete magnetic field of a bar magnet looks like this: N S W G G W
The lines run from north pole to south pole.
The lines never cross each other.
Although the lines are drawn on a flat piece of paper, they are in fact all around the magnet in 3D.
The strongest magnetic force is where the lines are closest together.
The magnetic force will be greatest at (G) and weakest at (W).

14. There is no magnetic force.
MAGNETIC FIELDS
When two magnets come close together they alter each other’s magnetic field. The shape that the fields change to depends on whether the magnets are attracting or repelling each other.
Repelling N S
The magnets appear to push each others field away.
There are no field lines here. What can you say about the magnetic force?
Attracting N S
There is no magnetic force.
The field lines go from north to south. The force must be strong between the magnets because the field lines are close together.

15. MAGNETIC FIELDS
We said earlier that a compass follows the magnetic field of the Earth.
We can imagine Earth with a giant bar magnet inside it. Remember, the magnetic field is all around the Earth. N S
What is the pole of the north pointing end of a compass needle?
It is a south pole.
Earth does not really have a bar magnet inside.
So what do you think causes the magnetic field?
The Earth has a molten iron core which creates a magnetic field.

16. ELECTROMAGNETISM
If you put a plotting compass close to a wire that has an electric current flowing through it, the needle will move. This shows that there is a magnetic field around the wire.
But wire is usually made of copper and copper is not a magnetic material.
That’s right. So what do you think causes the magnetic field?
Is it the flow of electric current?
Correct!
Plotting compass needle moves.
Electric current.
A copper wire with no electric current flowing.
A copper wire with an electric current flowing.

17. Notice that the magnetic field lines are circular.
ELECTROMAGNETISM
If we plot the magnetic field for a single wire we can see that it is not very strong.
Notice that the magnetic field lines are circular.
The strength of the magnetic field can be increased by coiling the wire.
The force lines go anticlockwise if the electric current flows down the wire.
If coiling the wire increases the strength of the magnetic field, how can the strength be increased even more?
Use more coils of wire.

18. Why can we not just keep increasing the electric current?
ELECTROMAGNETISM
We can also increase the magnetic force by increasing the electric current flowing through the coiled wire.
Lastly, the magnetic force can be increased by winding the coil around a core of magnetic material.
Soft iron is the best material for the core because when the electric current is turned off it loses its magnetism. Steel cannot be used because it would not lose its magnetism.
Soft Iron Core.
Why can we not just keep increasing the electric current?
Because the coil would heat up and eventually melt.
What happens to the tiny magnets in the core when the electric current is turned on and off?
When the current is on the tiny magnets all line up and point the same way.
When the current is turned off the tiny magnets point in any direction.

19. USES OF ELECTROMAGNETISM
Perhaps the most well known use is in a scrap yard or car breakers to move scrap metal or scrapped cars around.
Electric current is flowing, the soft iron is magnetised and the car is lifted.
Electric current turned off, no magnetism and the car is released and dropped.
No electric current is flowing, no magnetism in the core.

20. ELECTROMAGNETISM
Another everyday use is in automatic door locks e.g. car door central locking or key coded security doors in banks and safes.
Door
Wall
Bolt
With the door closed and locked, the bolt, which is attached to the soft iron core, is held in place.
When the switch is activated and a current flows through the coil, the soft iron core is magnetised and moves to the left, withdrawing the bolt from the door allowing it to be opened.
Direction of core movement.

21. CHECK YOUR LEARNING Magnets can be thought to be made up of ?
What are the ends of a magnet called?
If you put the ends of two magnets together what happens?
Where is the magnetic force the strongest?
Name the most common magnetic metals.
How can the Earth’s magnetic field be thought of?
Describe what happens when an electric current flows through a wire.
How can the electromagnetic force be increased?

22. CHECK YOUR LEARNING - ANSWERS
We can think of magnets being made up of lots of tiny magnets all lined up.
Magnets have two poles, a North and a South.
Like poles will repel each other and unlike poles will attract each other.
The magnetic force is strongest at the poles.
Steel, Cobalt & Nickel.
The Earth has its own magnetic field which can be thought of as a bar magnet with a North and a South pole.
When an electric current flows through a wire, a magnetic field is created and an electromagnetic force produced.
The electromagnetic force can be increased by increasing the electric current, having a coil with many turns of wire or by using a soft iron core within the wire coil.