MAGNETISM

We can see magnetic field lines with the aid of a sprinkle of IRON FILINGS.

Well, we can’t see it for a start, but... 8J What does a magnetic field look like? Well, we can’t see it for a start, but... Small particles of iron filings are pushed into patterns by a magnetic field. If we sprinkle iron filings on a piece of paper over a magnet we can see... The lines of force are very close together here – the field is very strong. The lines of force are further apart here – the field is weaker. A line of force links one pole of a magnet to the other pole.

Field lines The direction of the MAGNETIC FORCE is NORTH TO SOUTH

The magnetic force acts in a direction. 8J And the rule about directions... The magnetic force acts in a direction. The arrowheads on this diagram show you the way the needle of a compass point would go if it was free to move. You can see that the magnetic force runs from the north pole to the south pole of the magnet.

8J And now a few experiments... What happens?

TWO MAGNETS SHOWING Magnetic fields Does this show ATTRACTION or REPULSION?

TWO LIKE POLES TOGETHER WILL HAVE A FORCE OF 8J Turn one of the magnets around? TWO LIKE POLES TOGETHER WILL HAVE A FORCE OF REPULSION Can you explain what the lines of force show? Where is the strongest part of the field?

Two unlike POLES give a FORCE OF ATTRACTION 8J And now two magnets... Two unlike POLES give a FORCE OF ATTRACTION Can you explain what the lines of force show? Where is the strongest part of the field?

Match each word to its correct meaning. 8J A few words to start you off Match each word to its correct meaning. C attracts a magnetic material to a magnet F force that pushes two objects apart B not attracted to a magnet D the end of a freely suspended magnet that faces north E attracted to a magnet A the two ends of a magnet A the two ends of a magnet B not attracted to a magnet D the end of a freely suspended magnet that faces north F force that pushes two objects apart E attracted to a magnet C attracts a magnetic material to a magnet 1 magnetic force 2 repulsion 3 non-magnetic 4 north-seeking pole 5 magnetic 6 poles

Not all magnetic materials are magnets. 8J Magnets, magnetism and magnetic materials A magnetic material is something that is attracted by a magnet, for example, a steel paper clip. Not all magnetic materials are magnets. A magnet is a piece of magnetic material with a north and south pole. Magnetism is the force that pulls the opposite poles of two magnets together or pushes the same poles of two magnets apart. Ancient Greeks identified a naturally magnetic rock 2500 years ago – do you know what it is called?

1. Aluminium is not magnetic. 8J What do you think? True or false? 1. Aluminium is not magnetic. 2. Some magnets also have an east and west pole. 3. Magnets attract materials made of iron. 4. South poles attract each other. TRUE FALSE

2. If you break a magnet, you get two smaller magnets. 8J What do you think? True or false? 1. The magnetic field is the area around a magnet where the magnetic force can be felt. 2. If you break a magnet, you get two smaller magnets. 3. The north pole of a magnet is always stronger than the south pole. 4. Some magnets only have a north pole. TRUE FALSE

Field is a word we all understand – it’s a place with lots of grass! 8J What’s a field? Field is a word we all understand – it’s a place with lots of grass! But scientists also use the word ‘field’ with another meaning. A field is an area where a force acts. So, a magnetic field is the area where a magnet could attract something. Can you think of any other sort of field in science?

1. Iron filings can be used to show the shape of the magnetic field. 8J Magnetic fields – true or false? True or false? 1. Iron filings can be used to show the shape of the magnetic field. 2. Magnetic field lines always go out of the north pole. 3. Magnetic field lines come out of both ends of a magnet. 4. Magnetic materials placed in the magnetic field will be attracted towards the magnet. TRUE FALSE

8J Magnets and electromagnets Electromagnetism

They obey the same rules as magnetic fields. 8J Fields around wires A wire carrying an electric current also shows magnetic field lines around it. They obey the same rules as magnetic fields. The closer the lines are together the stronger the force. But does this attract or repel a magnet? That depends on which way the current is flowing.

What else creates field lines like this? 8J Fields in coils of wires Electricity passing through a coil of wire produces a magnetic field. Look at the diagram below to see the lines of force. What else creates field lines like this? What happens to the field if you put a bar of iron inside the coil?

Describe what is happening here. 8J Using electromagnets – alarm bells Describe what is happening here.

b) an invisible force that pushes or pulls magnetic materials 8J Test your magnetism 1. What is magnetism? a) a kind of glue b) an invisible force that pushes or pulls magnetic materials c) something that an attractive person has. 2. Which of the following metals can be magnetised? a) copper b) aluminium c) iron.

3. All magnets are surrounded by... a) metal b) a magnetic field 8J Test your magnetism 3. All magnets are surrounded by... a) metal b) a magnetic field c) fluff. 4. Where is the Earth’s magnetic north pole? a) close to the South Pole b) close to the North Pole c) at the North Pole in Summer and the South Pole in winter.

5. If magnetic field lines are close together it means... 8J Test your magnetism 5. If magnetic field lines are close together it means... a) the magnetic field is very strong b) the magnetic field is very weak c) there’s not much space for the field to spread into. 6. A wire carrying a current... a) continues to act like a magnet when the current is switched off b) produces circular magnetic field lines c) produces no magnetic field.