The picture and text for principle of magnet mutual attraction and mutual repulsion
In the middle school, physics book writed that magnets have S poles and N poles. If put the two S poles or two N poles of the two magnets together, there is a repulsive force between them; if put an N pole and an S pole together, There is suction between them.
The forces that attract or repel each other are magnetic forces. They are generated in the magnetic field. Faraday introduces the concept of magnetic induction line in order to interpret the magnetic field. The magnetic induction line is a closed curve that is specified artificially and does not actually exist. From S to N inside the magnet, the outside is from N to S. The magnetic induction line is attractive when it is in the same direction, and the repulsive force is in the opposite direction. When there is a certain angle, the magnet has a tendency to rotate, and the direction of the magnetic induction line is uniform. In general, the magnetic induction line is not objective exist. It is just a concept introduced by people to study the forces in the magnetic field and the phenomenon of electromagnetic induction.
According to quantum electrodynamics, the essence of electromagnetic interaction force (isotropy mutual repulsion, anisotropy mutual attraction) is the result of constant exchange of photons between two particles. The two electrons are close to each other and eventually bounce off due to electromagnetic force. What happened to this? It turns out that the two electrons are exchanging photons constantly. Imagine people on two skating rinks who keep throwing a ball and throwing it away from one person to another, so they must be farther and farther apart, it seems that there is a repulsive force between them. In the electromagnetic force, this ball is a photon! So what is the anisotropy mutual attraction? You can imagine two people standing back to back, without stopping, throwing the ball on the wall facing each other and bounce back into opposite person’s hand, so there seems to be a suction to hold them together.
The article belongs to the magnet industry news column, column links: http://www.couragemagnet.com/news/hyxw/