12.2 Permanent Magnets

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In the photo to the right, tiny iron filings cling to the end of a bar magnet.  This should be no surprise because it is known that bar magnets can exert a force on other magnets and that some metals, such as iron, are easily attracted to bar magnets.  This photo supports these observations.  But it does more; the tiny bits of iron have collected along the lines of the magnetic field, hinting at its shape near the pole.  

Magnetic Field:  a three-dimensional region of magnetic influence surrounding a magnet in which other magnets or magnetic substances are affected by magnetic forces

Each of the tiny filings of iron that are sprinkled near the bar magnet in the photo acts like a tiny compass.  When the filings land they align themselves with the bar magnet's magnetic field and reveal two dimensions of its shape.  Like the electrical field between two oppositely charged point charges, the magnetic field has two poles, one at either end of the bar magnet.  Like electric charges, like poles repel and unlike poles attract.  The field is three-dimensional in nature, as observed in the interactive tutorial that follows.