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Lines of force
Magnetic lines of force - according to the lexicon also field lines or magnetic field lines - are linear structures that depict the flux within a magnetic field. However, not only the direction of the acting magnetic forces can be read from them. They also indicate how strong the magnetic field is in each individual area around the magnet.
The concept of the field must be specified more precisely. While the lines of force in a magnetic force field move within a closed system and independently of a positive or negative charge, field lines in an electric force field run without such a limitation. They are also dependent on a charge source.
How do lines of force work?
A so-called pole is located at both ends of a rod or horseshoe magnet. This is an area in the immediate vicinity of which there is a particularly high magnetic field strength. Each of these two magnetic fields is influenced by the other due to the usually small distance between the two poles.
To simplify matters, we assume that the field lines enter at the south pole of a magnet and exit again at the north pole. Inside a coil or a bar magnet, the field lines are parallel to one another in the corresponding direction. Outside the magnet, they form crescent-shaped lines, as they do not touch each other and still run back on the shortest possible path from the north to the south pole. The field lines are therefore self-contained. There is no recognizable beginning or end.
If the north pole of the rodmagnet is now positioned in the immediate vicinity of a ferromagnetic object, the lines of force pass into it. The ferromagnetic body becomes magnetized, the newly created south pole of which is directed towards the north pole of the magnet. Then the field lines run back from the north pole of the magnetized body to the magnet's south pole.
What significance do magnetic lines of force have?
Magnetic lines of force provide the viewer with diverse information. For example, to:
- Strength of the magnetic field at different points
- Direction in which the force of the magnetic field acts
- Permeability and magnetic saturation of a metallic substance
They are particularly useful for measuring the strength of a magnetic field at each individual point around the magnetic body, since the field line density allows direct conclusions to be drawn about the magnetic field strength that prevails at the respective point. Different metals offer the lines of force different amounts of space. Related to this, some metals become magnetically saturated much faster than others. The field lines also allow conclusions to be drawn about how suitable certain substances are regarding their permeability and saturation behavior.
In addition, magnetic lines of force convey knowledge about the direction in which the magnetic field radiates. For example, if you put iron powder on a sheet of paper, place a bar magnet underneath and gently shake the sheet, the powder will be arranged along the lines of force. The reason for this is the prevailing magnetism, which turns the small iron particles into countless individual, small magnets. The heavier particles stick to the magnetic poles and pull the lighter, smaller iron filings towards them.
It can be seen not only that the magnetic field is strongest at the poles of the magnet, but also the course of the field lines becomes clear and thus the direction in which the force of the magnetic field acts. The lines of force radiate out in straight lines at the ends of the magnetic poles and from there run in gradually increasing arcs to one another, since they cannot intersect due to the mutual repulsion effect. The direction of the lines of force and thus that of the magnetic force field is also displayed when a small, freely movable magnetic needle is inserted into the field.