Magnet | Polar Regions, Neutral Region, Poles, Axis, Length

A magnet is a substance having attractive and directive properties. Chemical formula of a magnet is Fe₃O₄.

General Properties of a Magnet

A magnet has attractive property i.e. it exerts magnetic force on a magnetic substance and hence it attracts the magnetic substance.
A magnet has directive property i.e. if it is freely suspended, it will come to a position close to the north-south direction.
A magnet has two poles; North and South. These poles are of equal strength.
Like poles repel and unlike poles attract each other.
Magnetic poles always exist in pair. If we break magnet into pieces, each piece will contain two new poles. If these poles are again broken, then each new piece will also contain a north and a south pole. Hence, every tiny piece is a magnet.

Polar Region

The region near the ends of a magnet where there is attraction or repulsion is called polar region. A magnet has two polar regions; North polar region and South Polar region.

Neutral Region

The region at the middle portion of a magnet where there is neither attraction nor repulsion is called neutral region.

Poles of a Magnet

The point in the polar region through which the resultant of all acting forces in polar region of the magnet acts, is called magnetic pole. There are two poles of a magnet due to two polar regions; North pole and South pole.

When a magnet is freely suspended, the pole which lies in the geographical north side is called North pole and the pole which lies in the geographical south side is called South pole. In modern science, the magnetic north pole is known as positive magnetic charge and the magnetic south pole is known as negative magnetic charge.

Magnetic Axis

The line passing through the both poles of a magnet is called its magnetic axis.

End-on-position

A point lying on the magnetic axis is called end-on-position. In the figure given below, $X’OX$ is magnetic axis and the point $P$ is end-on-position.

Magnetic Length

The distance between poles of a magnet is called magnetic length or effective length. In the figure given below, $NS=2l$ is the magnetic length of the magnet and $l$ is semi-magnetic length.

Geometric Length

The distance between the ends of a magnet is called geometric length or real length or actual length. In the figure given below, $L$ is the geometric length.

For any magnet, the ratio of magnetic length and geometric length is constant i.e. \[\frac{\text{Magnetic length}} {\text{Geometric length}}=0.85\]

The magnetic centre of a magnet may not coincide with geometric centre of the magnet because in a magnet, geometric axis may not coincide with magnetic axis.

Magnetic Equator

A perpendicular bisecting line to the magnetic length of a magnet is known as magnetic equator.

Broad side on position

A point lying on the magnetic equator is known as broad side on position. In the figure given below, $YOY’$ is magnetic equator and the point $P$ is broad side on position.