A magnetic field line is an imaginary line used to illustrate a magnetic effect.

Magnetic field lines represent the direction and strength of the magnetic field around a magnet or a current-carrying wire. The magnetic field lines are imaginary lines that show the direction a small compass would point if placed at any point in the magnetic field.

The direction of the magnetic field lines is defined as the direction of the magnetic force that would be experienced by a positive test charge moving in the field. The field lines always form closed loops, and the density of the lines represents the strength of the magnetic field at a given point.

The convention for drawing magnetic field lines is to remove them from the magnet’s north pole to the south pole, and the field lines outside the magnet always point from the south pole to the north pole.