Magnetic field is one of forms of matter, objective reality. It is invisible to a human eye, but its existence is shown in the form of the magnetic forces making impact on charged particles and permanent magnets.
Graphic representation of magnetic field
Magnetic field is invisible by the nature. The way of its graphic representation in the form of power lines was developed for convenience. Their direction has to coincide with the direction of forces of magnetic field. Power lines have no beginning and the end: they are closed. It reflects one of Maxwell's equations in the theory of electromagnetic interaction. It is accepted scientific community that power lines "begin" on the North Pole of a magnet and "come to an end" on southern. This addition was made only for a conditional task of the direction of a vector of force of magnetic field.
It is possible to make sure of isolation of power lines of magnetic field by means of simple experience. It is necessary to strew a permanent magnet and area around it with iron sawdust. They will be located in such a way that you will be able to see power lines.
Tension of magnetic field
The vector of tension of magnetic field is also that vector described in the previous section. Its direction has to coincide with the direction of power lines. It is force with which the field affects the permanent magnet placed in it. Tension characterizes interaction of magnetic field with surrounding substance. There is a special formula by which it is possible to define the module of its vector in any point of space (Biot-Savart-Laplace's law). Tension does not depend on magnetic properties of the environment and is measured in oersteds (in the SGS system) and in the Car (SI).
Induction of magnetic field and magnetic flux
Induction of magnetic field characterizes its intensity, i.e. ability to perform work. Than this ability is higher, that the stronger sex and concentration of power lines in 1 sq.m is higher. The magnetic flux is performing induction on the square which the field influences. In number this size can be equated to the number of the power lines penetrating a certain area. The stream is maximum if the platform is located perpendicularly to the direction of a vector of tension. The less this corner, the is weaker influence.
Magnetic permeability
Action of magnetic field in a certain environment depends on its magnetic permeability. This size characterizes induction size in the environment. Air and some substances have magnetic permeability of a vacuum (the value undertakes from the table of physical constants). In ferromagnetics it in thousands times more.