A magnetic field is the space around a magnet that exerts a force on magnets and magnetic materials.
Like all forces, magnetic forces have direction. The directions of forces in a magnetic field are represented by magnetic field lines.
Fig. 18.1.2 Magnetic field lines
The direction of these lines can be seen if you place a compass near enough to a magnet so it will experience a magnetic force.
A compass is a small magnet that moves freely to show direction. The direction the compass needle points is the direction of the magnetic field lines.
Magnetic field lines always run from the north to south pole of the magnet.
Fig. 18.1.3 A compass needle can be moved by a magnet Seeing magnetic fields
1. Place a bar magnet inside a plastic pocket folder. Next, place a sheet of paper on top of the plastic folder. Scatter some iron filings on top of the sheet of paper.
2. Draw a diagram of what you see. Can you identify where the magnetic field is at its strongest? Using a plotting compass
A plotting compass is a small compass that you will most likely find in the school laboratory. Using a plotting compass, plan, design, carry out and write up an investigation to verify that the picture of the magnetic field lines in Fig. 18.1.2 is correct.
Linking ideas
Compare the magnetic field lines in Fig. 18.1.2 with your observations when you sprinkled iron filings over the bar magnet. Based on your comparison, write a statement describing the relationship between the strength of magnetic fields and the distance between the magnetic field lines.
