Using field lines, one can not only show the direction of the magnetic field, but also characterize the magnitude of its induction.
We agreed to draw the lines of force in such a way that through 1 cm² of the platform, perpendicular to the induction vector at a certain point, a number of lines pass equal to the field induction at that point.
In the place where the induction of the field will be greater, the lines of force will be thicker. And, conversely, where the field induction is less, less often and field lines.
Thus, by the density of the lines of force of the magnetic field they judge the magnitude of the vector of its induction, and by the direction of the lines of force - the direction of this vector.
Observation of the magnetic spectra of the direct current and the coil shows that with the removal of the conductor, the magnetic field induction decreases, moreover, very quickly.
A magnetic field with unequal induction at various points is called inhomogeneous. An inhomogeneous field is a rectilinear and circular current field, a field outside the solenoid, a permanent magnet field, etc.
A magnetic field with the same induction at all points is called a homogeneous field. Graphically, a magnetic homogeneous field is represented by lines of force, which are parallel lines equally spaced from each other .
An example of a uniform field is a field inside a long solenoid, as well as a field between parallel parallel flat pole tips of an electromagnet closely spaced.
The product of the induction of the magnetic field penetrating a given circuit into the area of the circuit is called magnetic flux of magnetic induction, or simply magnetic flux.
The English physicist Faraday gave a definition to him and studied his properties. He discovered that this concept allows a deeper look at the unified nature of magnetic and electrical phenomena.
Denoting the magnetic flux by the letter , the area of the circuit S and the angle between the directivity of the induction vector B and the normal n to the area of the circuit α, we can write the following equality:
= S cos α.
Magnetic flux is a scalar quantity.
Since the density of the lines of force of an arbitrary magnetic field is equal to its induction, the magnetic flux is equal to the entire number of lines of force that permeate this circuit.
With a change in the field, the magnetic flux that permeates the contour also changes: when the field is strengthened, it increases, when weakened, it decreases.
For a unit of magnetic flux in the SI system, a flux is adopted that permeates a 1 m² area located in a uniform magnetic field with an induction of 1 Wb / m² and perpendicular to the induction vector. Such a unit is called a weber:
1 Wb = 1 Wb / m² ˖ 1 m².
A changing magnetic flux generates an electric field having closed field lines (vortex electric field). Such a field is manifested in the conductor as an action of extraneous forces. This phenomenon is called electromagnetic induction, and the electromotive force that occurs in this case is the EMF of induction.
In addition, it should be noted that the magnetic flux makes it possible to characterize the whole magnet (or any other sources of magnetic field) as a whole. Therefore, if magnetic induction makes it possible to characterize its action at any single point, then the magnetic flux is entirely. That is, we can say that this is the second most important characteristic of the magnetic field. So, if magnetic induction acts as a force characteristic of a magnetic field, then magnetic flux is its energy characteristic.
Returning to the experiments, we can also say that every coil coil can be imagined as a single closed loop. The same circuit through which the magnetic flux of the magnetic induction vector will pass. In this case, an induction electric current will be noted. Thus, it is under the influence of magnetic flux that an electric field is formed in a closed conductor. And then this electric field forms an electric current.