Field lines | Magnet-Lexicon / Glossary |

Field lines

In physics, magnetic lines are the lines that graphically represent the course of a magnetic field and thus the force and properties of a magnet. They make the respective magnetic field lines visible during a test charge and are recorded schematically. The stronger the respective magnetic field, the closer the field lines are displayed. This force is described in the magnetic field strength H.

When Michael Faraday (1791-1867) examined the force effect of bar/ rod magnets, he also introduced the field lines with the concept of the magnetic field. The so-called field line images are purely illustrative models to better describe the properties of magnetic fields of all kinds. They are also relevant when considering the force effect of magnets of all kinds.

The differences between magnetic and electrical field lines

In physics, a distinction is made between two different types of field lines:

  • Electric field lines starting from a point on a charged body. These are linear in space. They start with a positively charged body and end with a negatively charged object.
  • Magnetic field lines, these always assume a magnetic north pole. They are self-contained, so they have no beginning and no end.
The electric field line model therefore draws line images, while the magnetic field line model describes magnetic circles.

How do field lines run with a magnet?

Magnetic field lines are generally vertical and circular from the north to the south pole of a magnet. The respective direction, i.e. the course, is thus clearly specified. If you put a compass needle in the field of a magnet, it would always point towards the North Pole. In this way, the two poles of a magnet can also be determined quickly.

Another special feature is that the lines do not end at the south pole, but run through the entire body to the magnetic north pole. This is because there is no origin and no source of these magnetic forces. Physically, this means that the field lines show no positive or negative charge, such as with electrical charges. In the case of field lines of an electrically charged object, for example a coil, the forces migrate from a source in a linear direction. The density of the magnetic field lines illustrates the force of the magnet.

Why can't field lines intersect?

Field lines are always closed lines with no end and beginning. This is because the magnetic field, which is mathematically described by the Maxwell equation, is a so-called vortex field. They always run side by side in parallel. This is clearly defined by the direction of force towards a magnetic north pole.

Do different types of magnets draw different field line images?

The course of the field lines is independent of different magnet types. They always run in a ring from the north to the south pole and through the material. The position of the poles is important for the different shapes and the respective field line images. The poles of these magnetic field lines are different:

  • Ring magnet
  • Rod / Bar magnet
  • Disc magnet
  • Horseshoe magnet
The arrangement of the poles changes the field line images graphically. This means that the force of the magnet can also be used differently.