MAGNETIC FIELD

When a bar magnet is placed on a plane horizontal wooden board and iron fillings are sprinkled on the surface of the plane around the magnet, the plane being gently tapped and all the iron fillings arrange themselves in a definite pattern along certain lines. This gives an evidence of the magnetic stress which exists in the space around the magnet. This region of stress, surrounding a magnet, is known as the Field due to Magnet.

If the lines along which the iron fillings set themselves near the ends of the bar magnet are extended into the magnet, they would be seen to concentrate themselves in two particular regions near each end of the magnet. These regions, are called as Poles of the Magnet.

The quantity of iron fillings sticking to the magnet is maximum at the ends and minimum at the central portion. This simply means that the force of attraction goes on increasing as we approach the ends or the poles from the center of the magnet.

Arrangement of Iron Fillings around Bar Magnet

The strength and position of the poles depend upon the shape and characteristic of the magnet. If the magnet is long-one with small cross-sectional area, the regions of maximum magnetic force, near the ends of the magnet are small. The poles of such a magnet are usually referred to as point pole.

When the bar magnet is freely suspended, the end which points to the north is called the North-seeking pole or simply the north pole and the other end, i.e., the one which points to the south as the South-seeking pole or simply the south-pole.

The imaginary line joining the two poles of a magnet is known as Magnetic-Axis, and a plane taken at right angles to the magnetic axis and through a point mid-way between the poles, is called the neutral-zone or equator of the magnet.