Elementary Charge

e, the smallest electric charge known in nature. The existence of the elementary charge was first mentioned with certainty by the British scientist G. Stoney in 1874. Stoney’s hypothesis was based on the laws of electrolysis established by M. Faraday (1833–34). In 1881, Stoney was the first to calculate the magnitude of the electric charge of a univalent ion, equal to e = F/N_A, where F is the faraday constant and N_A is Avogadro’s number. In 1911 the elementary charge was established by R. Millikan through direct measurements.

The presently accepted value of e is

e = (4.803242 ± 0.000014) × 10^–10 cgse units

= (1.6021892 ± 0.0000046) × 10^–19 coulomb

The magnitude of the elementary charge is the constant of the electromagnetic interactions, which appears in all equations of microscopic electrodynamics. The elementary charge is exactly equal to the electric charge of the electron, proton, and nearly all other charged elementary particles, which by virtue of this fact are the material carriers of the smallest charge in nature.

The elementary charge cannot be destroyed, and it is this fact that constitutes the content of the law of conservation of electric charge on the microscopic level. There is a positive and a negative elementary charge; in this case, an elementary particle and its antiparticle have charges of opposite sign. The electric charge of any microsystem and of macroscopic bodies is always equal to an integral multiple of the quantity e or to zero. The reason for such “quantization” of charge has not been established. One hypothesis is based on the existence of Dirac monopoles (seeMAGNETIC MONOPOLE). A hypothesis positing the existence of particles with fractional electric charges—quarks—has been much discussed since the 1960’s (seeQUARK and ).