elementaarlaeng

Elementaarlaeng, or elementary charge, is the fundamental unit of electric charge. It is the magnitude of the charge carried by a single proton or by a single electron, the latter having the opposite sign. The symbol for the elementary charge is e, and its exact value is 1.602176634 × 10^-19 coulombs. In ordinary matter, electric charge is observed only in integer multiples of e, a principle known as charge quantization. Particles called quarks carry fractional charges (±2/3 e and ±1/3 e), but they do not exist freely due to confinement; composite particles such as protons and neutrons have net charges that are integer multiples of e.

The elementary charge is a fundamental physical constant. Its magnitude is determined experimentally, with Millikan’s oil-drop experiment historically contributing to the precise measurement of e. In contemporary physics, e is treated as a defined constant in the SI system.

Since the 2019 redefinition of SI units, the elementary charge is defined as an exact quantity: e = 1.602176634 × 10^-19 coulombs. This fixes the relationship between the coulomb and the ampere, tying electrical charge to fundamental constants of nature.

In practice, the elementary charge appears in many contexts, including Coulomb’s law, the quantization of charge in quantum mechanics, and the description of electronic charge transport, where charges are often expressed as multiples of e. The proton carries +e, while the electron carries −e, establishing e as the common unit for describing positive and negative electric charges.