Physics AQA GCSE P15.1
About magnets
A magnetic compass is a tiny magnetic needle pivoted at its centre.
Because of the Earth's magnetic field, one end of the compass always points north, and the other end always points south. The end of a plotting compass or a bar magnet (Figure 1) that points north is the
'north-seeking' pole, usually called its north pole (N-pole), and the other end is the 'south-seeking' pole, its south pole (S-pole).
north
Investigating bar magnets
Suspend a bar magnet as shown in Figure 1 and label the end that points north as its N-pole.
Hold the N-pole of a second bar magnet near the suspended bar magnet. You should find it attracts the S-pole of the suspended bar magnet and repels the N-pole.
Repeat the above test using the S-pole of the second bar magnet. You should find it attracts the N-pole of the suspended bar magnet and repels its S-pole.
Figure 1 Checking the poles of a bar magnet
lines of force
plotting compass
Figure 2 The magnetic field of a bar magnet a Using iron filings b Using a plotting compass
214
The tests above show the general rule that:
Like poles repel. Unlike poles attract.
Magnetic materials
Any iron or steel object can be magnetised (or demagnetised if it's already magnetised). Only a few other materials (for example cobalt and nickel) can be magnetised and demagnetised. Permanent magnets are made of steel because magnetised steel does not lose its magnetism easily.
Magnetic fields
If a sheet of paper is placed over a bar magnet and iron filings are sprinkled onto the paper, the filings form a pattern of lines. The region around the magnet is called a magnetic field. Any other magnetic material placed in this space experiences a force caused by the first magnet.
In Figure 2:
the iron filings form lines as shown in Figure 2a that end at or near the poles of the magnet. These lines are magnetic field lines, also called lines of force. The lines are more concentrated at the poles than elsewhere. This is because the field is strongest at the poles.
a plotting compass placed in the magnetic field aligns itself along a magnetic field line, pointing in a direction away from the N-pole of the magnet and towards the magnet's S-pole, as shown in Figure 2b.
For this reason, the direction of a line of force is always from the north pole of the magnet to its south pole.
About magnets
A magnetic compass is a tiny magnetic needle pivoted at its centre.
Because of the Earth's magnetic field, one end of the compass always points north, and the other end always points south. The end of a plotting compass or a bar magnet (Figure 1) that points north is the
'north-seeking' pole, usually called its north pole (N-pole), and the other end is the 'south-seeking' pole, its south pole (S-pole).
north
Investigating bar magnets
Suspend a bar magnet as shown in Figure 1 and label the end that points north as its N-pole.
Hold the N-pole of a second bar magnet near the suspended bar magnet. You should find it attracts the S-pole of the suspended bar magnet and repels the N-pole.
Repeat the above test using the S-pole of the second bar magnet. You should find it attracts the N-pole of the suspended bar magnet and repels its S-pole.
Figure 1 Checking the poles of a bar magnet
lines of force
plotting compass
Figure 2 The magnetic field of a bar magnet a Using iron filings b Using a plotting compass
214
The tests above show the general rule that:
Like poles repel. Unlike poles attract.
Magnetic materials
Any iron or steel object can be magnetised (or demagnetised if it's already magnetised). Only a few other materials (for example cobalt and nickel) can be magnetised and demagnetised. Permanent magnets are made of steel because magnetised steel does not lose its magnetism easily.
Magnetic fields
If a sheet of paper is placed over a bar magnet and iron filings are sprinkled onto the paper, the filings form a pattern of lines. The region around the magnet is called a magnetic field. Any other magnetic material placed in this space experiences a force caused by the first magnet.
In Figure 2:
the iron filings form lines as shown in Figure 2a that end at or near the poles of the magnet. These lines are magnetic field lines, also called lines of force. The lines are more concentrated at the poles than elsewhere. This is because the field is strongest at the poles.
a plotting compass placed in the magnetic field aligns itself along a magnetic field line, pointing in a direction away from the N-pole of the magnet and towards the magnet's S-pole, as shown in Figure 2b.
For this reason, the direction of a line of force is always from the north pole of the magnet to its south pole.
