Exhibiting magnetic field patterns

Here are five ways of exhibiting magnetic field patterns:

• Large posters of magnetic fields can be plotted out with a compass to make a classroom display.
• Paper can be waxed with paraffin wax and placed on top of a magnet. After the iron filing pattern is produced, melt the wax slightly with a candle placed underneath the waxed paper. When the candle is removed and the paper cooled, the iron filings stick to the paper. This method was used by Faraday.
• An iron filing pattern can be made permanent by spraying gently with hair spray (lacquer).
• Student or teacher can make a quick demonstration using an overhead projector. Instead of covering the magnet with card, before sprinkling iron filings, place a piece of transparent plastic on top of the magnet. Sprinkle iron filings on it.
• Photographs of magnetic fields can be produced by replacing the card with photographic paper. In the dark, or with a red safety light on, sprinkle iron filings onto the paper more densely than normal. Switch on the laboratory lights for 20 seconds. Then switch off the lights and shake the iron filings off the photographic paper. Develop the photographic paper in the normal way, taking the usual safety precautions when handling photographic developer.

Safety note: Warn the class to keep fingers away from eyes. Iron filings inadvertently carried to the eyes can damage the cornea.