In short
A magnetic field is the region around a magnet or a moving charge in which a magnetic force can be felt. It is drawn with field lines that run from the north pole to the south pole outside a magnet.
The field is strongest where the lines are closest together, which for a bar magnet is near its poles. A current in a wire makes a magnetic field around it, and a coil with many turns makes a field like a bar magnet's. The strength of the field is measured in tesla (T). A moving charge in a field feels the force .
Iron filings sprinkled round a bar magnet gather most thickly at the two ends, showing the field is strongest at the poles and weakest at the middle of the magnet.
Also searched as: where the magnetic field is strongest, magnetic fields.
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