Science 8th grade
UNIT 13: Magnetism 13.3 Magnetic field pattern
Science 8th grade
UNIT 13: Magnetism 13.3 Magnetic field pattern
Magnets are surprising. A magnet can attract a piece of magnetic material without touching it.
We say that a magnet is surrounded by a magnetic field. Any magnetic material placed in the field will be attracted by the magnet.
The shape of the field
A magnetic field is invisible. Here are two ways to show up the shape of the magnetic field around a bar magnet:
• Use iron filings. These tiny pieces of iron cluster together and line up to show the pattern of the field.
• Use small compasses called plotting compasses. They show the direction of the field.
Magnetic field lines
We can represent the magnetic field of a magnet by drawing magnetic field lines. These are imaginary lines.
Magnetic field lines start from a north pole and end up at a south pole. They show two things about the field:
• The arrows show the direction of the field.
• Where the lines are closest together is where the field is strongest.
|
|
Questions
1) Look at the diagram of the field lines around a bar magnet.
Where is the field strongest? Explain how you can tell.
2) Compare the diagram of the field lines with the photograph.
In what ways are they similar?
Activity 13.3 (Investigating magnetic fields)
SE: 1) Use iron filings to show up the magnetic field of a bar magnet.
Safety! Take care to avoid getting the filings on your hands as you might rub them into your eyes.
2) Place two bar magnets so that their poles are attracting each other.
Investigate the shape of the magnetic field between them.
3) Repeat this with the magnetic poles repelling each other.
The magnetic Earth
People use a compass to help them find their way around.
A compass has a needle which is magnetised. The needle can turn round so it always points north-south.
A compass needle points north-south because the Earth has a magnetic field. It is as if there were a giant magnet inside the Earth. A compass points along the lines of the Earth's magnetic field.
Question
3) Look closely at the diagram of the Earth's magnetic field. Explain why the imaginary magnet inside the Earth is shown with a south pole at the top (the north end).
