A magnet is a special substance that can generate an invisible force field around it, which we call a magnetic field. A magnetic field can be represented by a virtual line called a magnetic field line, which starts from one end of the magnet and ends at the other end, forming a closed loop. If we place a small compass in a magnetic field, it will point along the direction of the magnetic field lines. If we bring two magnets closer, they will arrange their magnetic poles according to the law of opposite attracting and same repelling each other.

How does a magnet generate a magnetic field? To answer this question, we need to enter the microscopic world and look at the atoms and electrons inside the magnet. Atoms are the fundamental units of matter, composed of atomic nuclei and electrons. An atomic nucleus is composed of protons and neutrons, and it carries a positive charge. Electrons are small, light particles that carry negative charges and move around atomic nuclei. Charge is a fundamental physical quantity that can generate electric and magnetic fields. When the charge is stationary, it only generates an electric field; When a charge moves, it generates both an electric field and a magnetic field.

Electrons not only move around atomic nuclei, but also have an intrinsic motion called spin. Spin, like an electron rotating on its own axis, can also be seen as a tiny electric current. Therefore, each electron is equivalent to a small magnetic dipole, a system composed of two opposite magnetic poles. These small magnetic dipoles are the source of the magnetic field