Iron filings are commonly used as an effective way to demonstrate the magnetic field around a magnet.
Bar Magnet
If you place a bar magnet onto a piece of paper on a flat surface, and then sprinkle tiny iron filings on the piece of paper, the iron filings will form a distinct pattern around the magnet. The iron filings, each of which acts as a tiny magnet with a north and south pole, gather around the magnetic field lines. From the pattern, it becomes clear the magnetic force is strongest at the two ends of the magnet, as these areas attract the most iron particles.
Like Poles Repulse
Iron filings can be used to show the forces of repulsion between the like poles of two magnets. The magnets are placed with either their north or south poles facing each other on a piece of white paper. Iron filings are scattered around them, and the pattern that emerges shows a force of repulsion, with the iron filings shown to be moving away from the ends of the bar magnets.
Forces of Attraction
When the opposite poles of two magnets are placed facing each other on a piece of paper, the pattern that emerges after iron filings have been sprinkled shows the forces of attraction between the two magnets. The iron filings are attracted to the ends of the magnets and run in lines that bridge the gap between the magnets.
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