magnetic field

magnetic field around a bar magnet

Garnet. Credit: Mineral Information Institute.

A magnetic field is a field of force that is generated by a magnet and a conductor through which an electric current is flowing; or, equivalently, a region in which magnetic forces can be observed.


A magnetic field can be represented by a set of lines of force (flux lines) spreading out from the poles of a magnet or running around a current-carrying conductor. These lines of forces can be seen if iron filings are sprinkled on to a sheet of paper below which a magnet is placed. The filings line up along the lines of force, the density of the lines being greatest where the field is strongest. The direction of a magnetic field is the direction a tiny magnet takes when placed in the field.


Magnetic poles are the field region in which is magnetism appears to be concentrated. If a bar magnet is suspended to swing freely in the horizontal plane, one pole will point north; this is called the north-seeking or north pole. The other pole, the south-seeking or south pole, will point south. Unlike poles attract each other; like poles repel. Earth's magnetic poles are the result of the huge "magnet" that is the Earth.


Within a magnetic field a magnetic dipole may experience a torque and a moving charge may experience a force. A magnetic field with its associated electric field is called an electromagnetic field.