The curves which are used to represent the magnetic field, such that the number of lines represent the strength of the magnetic field at any point are called magnetic lines of force. The direction of magnetic force is given by the tangent of the curve at any point.

Properties of magnetic lines of force:

(i) These are closed curves which move from the N-pole to the S-pole and then return to the N-pole through the interior of the magnet. 

(ii) No two magnetic lines of force can intersect each other. 

(iii) Magnetic lines are continuous curves and they tend to contract longitudnally and expand laterally. This implies, attraction between unlike poles and repulsion between like poles.

(v) The relative closeness of the lines of force gives a measure of the strength of the magnetic field. It is found the magnetic strength is maximum at the poles.