|MadSci Network: Physics|
A magnetic field is the area surrounding (in 3 dimensions) any magnet or current carrying wire where a magnetic force can be detected. The Earth itself acts as if it contained a giant bar magnet and is totally surrounded by a magnetic field. If you suspend a bar magnet anywhere on Earth it will line up with the magnetic field - if you were at the magnetic north pole the north seeking pole of your magnet would be pointing downwards into the Earth. The lines of force or field lines are simply a way of describing the extent and the direction of a magnetic field. They are defined as the lines along which a tiny bar magnet in the magnetic field would lie along. The direction of the magnetic field is given by convention, its the direction in which the north seeking pole of the tiny magnet is pointing. So the lines of force go from the N pole to the S pole outside a magnet but from S to N inside a magnet. When two magnets are brought close together their magnetic fields interact making like poles repel one another and opposite poles attract. Current theories about magnets are listed at http://www.technicoil.com/magnetism.html
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