Conservation of Charge, Law of

Conservation of Charge, Law of

 

one of the absolute fundamental laws of nature, consisting in the fact that the algebraic sum (with consideration for sign) of the electric charges of any closed (electrically insulated) system remains unchanged no matter what processes transpire within the system. The law of conservation of charge was established in the 18th century.

The electron, a carrier of negative electric charge, was discovered at the end of the 19th century, and the proton, which has a positive charge of equal magnitude, was discovered at the beginning of the 20th century. It was thus proved that electric charges do not exist in and of themselves but are connected with particles and are an intrinsic property of particles (later other elementary particles carrying a positive or negative charge of equal magnitude were also discovered). The electric charge is discrete: the total charge of any body is an integral multiple of the elementary charge, which is equal in magnitude to the charge of an electron.

Insofar as every particle is characterized by a specific, inherent electric charge, the law of conservation of charge may be considered as a consequence of the conservation of the number of particles (in those physical phenomena in which interconversion of particles does not take place). On electrification of macroscopic bodies, the number of charged particles does not change and only a redistribution in space takes place. Thus, if bodies are charged as a result of friction (triboelectrification), the charged particles are transferred from one body to the other (a charge that is acquired by one body is lost by the other); thus, both bodies, which originally were electrically neutral, are charged with equal but opposite charges.

In the physics of elementary particles (the field of high-energy physics), characterized by the processes of interconversion of particles, the number of particles is not conserved—some disappear, others are created—but the law of conservation of charge is always strictly observed; the total charge remains unchanged during all interactions and conversions of particles. The creation of a new charged particle is possible only on the simultaneous disappearance of an “old” particle with the same charge or in a pair with another particle that has a charge of opposite sign (for example, in the process of the creation of particle-antiparticle pairs). During all such conversions the other laws of conservation—the law of conservation of energy and the law of conservation of momentum—must also be satisfied.

Together with the law of conservation of energy the law of conservation of charge “explains” the stability of the electron. The electron and the positron are the lightest of the charged particles and therefore cannot decay into anything else: decay into heavier charged particles (such as a muon or pi-meson) is forbidden by the law of conservation of energy, and decay into neutral particles lighter than the electron (such as photons or neutrinos) is prohibited by the law of conservation of charge. The precision to which the law of conservation of charge is satisfied can be judged from the fact that (as experience shows) the electron does not lose its charge for at least 1019 years.

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