This is the way magnetic field lines are distributed in a magnetic field. Figure below shows how magnetic field lines are distributed around a bar magnet and a horse-shoe magnet as revealed by a plotting compass;

Magnetic field lines plotted are observed to have the following properties:

1. They are considered to run from the North Pole to the South Pole.
2. Their concentration is a measure of the strength of the magnetic field. That is the closer the lines, the stronger the field. Therefore with the bar magnet, the field is stronger around the poles while with the horse-shoe magnet, the field is stronger in the space between the poles.
3. They tend to repel one another sideways.
4. They never cross one another.
5. They always try to shorten themselves like stretched elastic cords.

Field between magnets

If two magnets are placed under a cardboard paper and iron filings sprinkled on the cardboard paper, the two fields will combine to produce a single magnetic field or a resultant magnetic field. Some examples of resultant magnetic fields are shown in figure below;

The point X in figure (b) and (c) above is called the neutral point, defined as the point on a magnetic field where the resultant magnetic flux density is zero. That is, at X the magnetic fields cancel out and no magnetic force is felt.

Some types of magnetic fields

Some common magnetic fields include;

• The uniform magnetic field in which the field lines are uniformly distributed. E. g. the magnetic field of the earth.
• The non-uniform magnetic field in which the magnetic field lines are not uniformly distributed. E.g. the magnetic field between two magnetic poles
• The radial magnetic field in which the field lines are circular. E.g. the field around a current-carrying conductor.

These magnetic fields are shown in figure below;

THE EARTH’S MAGNETIC FIELD

The earth behaves as if there is a huge bar magnet buried in its core and inclined at a small angle to its axis of rotation, with its south pole at the northern hemisphere.

Therefore the earth's magnetic field lines run from the magnetic south to the magnetic north, as shown in figure below.

The needle of a plotting compass always aligns itself with the earth’s magnetic field if there is no other magnetic field around,