General laws of electrostatics

When an excess or lack of electrons is created in a body, the body becomes charged, carrying a charge Q. The value Q is always proportional to Id. However, at large Q (in comparison with Id), this discontinuity is not exhibited, so it is possible to consider the charge changing continuously. 

Electric charge is invariant with respect to Galileo transformations. 

If an electric system is closed, its total algebraic charged is preserved. 

The force of interaction of two point charges q and Q in a vacuum is defined by the Coulomb s law  

Coulomb s law has much in common with Newton s law of gravity in both laws, the same functional dependence on the distance (1/r ) is present. There is a profound physical meaning in this fact which we will consider below. There exists however an essential difference attraction between dissimilar charges and repulsion between similar charges are automatically taken into account in the Coulomb s law (i.e., Q and q are taken with their signs) however, in Newton s law, the negative sign of force always corresponds to the masses attraction. 

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