You have studied properties of electric lines of force earlier in the Chapter on electrostatics.
In a similar manner, magnetic lines of force originate from the North pole and end at the South pole.
The magnetic lines of force have the of a magnet following properties:
i) The magnetic lines of force of a magnet or a solenoid form closed loops. This is in contrast to the case of an electric dipole, where the electric lines of force originate from the positive charge and end on the negative charge.
ii) The direction of the net magnetic field B at a point is given by the tangent to the magnetic line of force at that point.
iii) The number of lines of force crossing per unit area decides the magnitude of the magnetic filed B .
iv) The magnetic lines of force do not intersect. This is because had they intersected, the direction of magnetic field would not be unique at that point.