Magnetic lines of force of a magnet shows the direction in which a magnetic material will be aligned when placed at the location. Magnetic field lines for a bar magnet are as shown in the diagram.
Properties of magnetic fields of lines
Magnetic field lines are imaginary lines that represent magnetic fields. It gives direction of magnetic force. An advantage of using magnetic field lines as a representation is that laws of magnetism and (electromagnetism) can be stated using concepts like 'number' of field lines through a surface.
Magnetic field lines are like streamlines in fluid flow, they represent something continuous, and a different resolution would show more or fewer lines. Various phenomena have the effect of displaying magnetic field lines as though the field lines were physical phenomena. For example, iron filings placed in a magnetic field, form lines that correspond to field lines. Field lines can be used as a qualitative tool to visualize magnetic forces.' Unlike' poles of magnets attract because they are linked by many field lines, 'like' poles repel because their field lines do not meet, but run parallel, pushing on each other.
The region or space around a magnet, within which its influence can be experienced is called magnetic field of that filed.
Intensity of Magnetic field
The intensity of magnetic field at a point in a magnetic field is defined as the force experienced by unit north pole when placed at that point.
Arrangement of iron fillings around a bar magnet
When iron filings are placed in magnetic field, they are magnetized and induce poles in them. Hence, they act as small magnets themselves. These filings orient themselves along the magnetic field lines of the bar magnet as shown in the figure.
The region surrounding the magnet, in which the force of the magnet can be experienced, is called magnetic field.