The phenomena in nature are very complicated. In order to explore the true features of natural laws, it is necessary to simplify the phenomena and objects studied, highlight the main contradictions and ignore the secondary factors. An ideal model or model is something that can reflect physical laws after simplifying phenomena or objects. It doesn't really exist in nature, but its characteristics are reasonable, such as Rutherford's hydrogen atom model. On the one hand, the model can help us understand concise physical laws; On the other hand, when the real phenomenon conflicts with the model, we can get a new theory by modifying or establishing a new model, or we can understand that the model is like a train timetable. Although the train often comes back late, it doesn't mean that the timetable is useless. On the contrary, the timetable can let you know that your train is late. In this sense, the model also reflects the gap between existing theories and facts.

The electrostatic field is irrotational, that is, the curl of the electrostatic field is zero; The divergence of static magnetic field is zero; The curl of electrostatic field is zero, which also shows that the electric field line starts from positive charge (or infinity) and ends at negative charge (or infinity), reflecting the existence of charge; However, the static magnetic field is not irrotational, the magnetic field lines are closed, and the magnetic monopole does not exist.