North and South Poles

Permanent magnets such as those used to hold the shopping list to the refrigerator, or those dug from the ground thousands of years ago in Magnesia to be used as compasses for navigation, have North (N) and South (S) poles. Opposites attract and likes repel. Magnetic fields and forces are thus similar to electric ones except for the feature that the N and S magnetic "charges" always come in the form of an equal-but-opposite pair.

The direction of the magnetic field B is defined as the direction of the force on a North pole. The full name of the N pole is North-seeking pole, so by definition the arrow on a magnetic compass points in the direction of B. Thus the head of the arrow on the compass needle is an N pole, but the magnetic field of the earth is roughly what would be produced by a bar magnet at its center with the N pole pointing toward antartica.

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