The general expression of Coulomb's theorem is that the interaction force between two static point charges in vacuum is directly proportional to the product of their charges and inversely proportional to the square of their distance. The direction of the interaction force is on their connection line, charges with the same name repel each other, and charges with different names attract each other. Coulomb's law is the first quantitative law in the history of electricity development, and it is also one of the basic laws of electromagnetism and electromagnetic field theory.

First, electrostatic field. Coulomb's law is applicable to the case that the field source charge is static and the forced charge is moving, but it is not applicable to the force of the moving charge on the static charge. Because the spatial distribution of electric field generated by static source charge does not change with time, the electric field force exerted by static source charge on moving charge follows Coulomb's law. The electric field force generated by the electric field excited by the moving charge does not obey Coulomb's law because the moving charge not only excites the electric field, but also excites the magnetic field. At this point, the coulomb force needs to be corrected to electromagnetic force. But practice shows that as long as the relative velocity of charge is much less than the speed of light C, the result given by Coulomb's law is very close to the actual situation.

Second, point charge. Coulomb's law only applies between point charges. The distance between charged bodies is much larger than their own size, so that the influence of shape, size and charge distribution on the interaction force can be ignored. When studying their interaction, people abstract it as an ideal physical model-point charge, and Coulomb's law only applies to the force between point charges. [