No doubt, the lines of force of the magnetic field are now known to everyone. At least at school, their manifestation is demonstrated in physics classes. Remember how a teacher placed a permanent magnet under a sheet of paper (or even two, combining the orientation of their poles), and on top of it poured metal filings taken in a labor training room? It is quite clear that the metal should have been kept on the sheet, however, something strange was observed - the lines along which sawdust were lined up were clearly visible. Note - not evenly, but in stripes. These are the lines of force of the magnetic field. Rather, their manifestation. What happened then and how can one explain it?
Let's start from afar. Together with us, in the physical world of the visible, a special form of matter coexists - a magnetic field. It provides the interaction of moving elementary particles or larger bodies with an electric charge or natural magnetic moment. Electrical and magnetic phenomena are not only interconnected with each other, but also often generate themselves. For example, a wire through which electric current flows creates lines of a magnetic field around itself. The converse is also true: the effect of alternating magnetic fields on a closed conductive circuit creates the movement of charge carriers in it. The latter property is used in generators that supply electrical energy to all consumers. A striking example of electromagnetic fields is light.
The magnetic field lines around the conductor rotate or, which is also true, are characterized by a directed magnetic induction vector. The direction of rotation is determined by the rule of the gimlet. The indicated lines are conditional, since the field spreads uniformly in all directions. The thing is that it can be represented as an infinite number of lines, some of which have a more pronounced tension. That is why in the experiment with a magnet and sawdust certain “lines” are clearly traced. Interestingly, the lines of force of the magnetic field are never interrupted, so you cannot say for sure where the beginning and where the end.
In the case of a permanent magnet (or an electromagnet similar to it), there are always two poles, which have received the conventional names of the North and South. The mentioned lines in this case are rings and ovals connecting both poles. Sometimes this is described from the point of view of interacting monopoles, but then a contradiction arises, according to which a monopole cannot be divided. That is, any attempt to divide the magnet will lead to the appearance of several bipolar parts.
Of great interest are the properties of lines of force. We have already talked about continuity, but of practical interest is the ability to create an electromotive force (EMF) in a conductor , the result of which is electric current. The meaning of this is as follows: if the magnetic field lines cross the conductive circuit (or the conductor itself moves in a magnetic field), then additional energy is transmitted to the electrons in the outer orbits of the atoms of the material, allowing them to begin independent directional motion. We can say that the magnetic field seems to “knock out” charged particles from the crystal lattice. This phenomenon is called electromagnetic induction and is currently the main way to obtain primary electrical energy. It was discovered experimentally in 1831 by the English physicist Michael Faraday.
The study of magnetic fields began as early as 1269, when P. Peregrin discovered the interaction of a spherical magnet with steel needles. Almost 300 years later, U. G. Colchester suggested that the globe itself is a huge magnet with two poles. Further, magnetic phenomena were studied by such famous scientists as Lorenz, Maxwell, Ampère, Einstein, etc.