Coulombs

Coulombs are the unit of electric charge in the International System of Units (SI). One coulomb (symbol C) is defined as the amount of charge transferred by a current of one ampere in one second, i.e., 1 C = 1 A × s. The coulomb is a derived unit, not a base unit, and it is used to quantify the amount of electric charge in objects and systems.

Charge is quantized in elementary units; the elementary charge e is approximately 1.602176634×10^-19 C. Thus, about 6.242×10^18 elementary charges make up one coulomb. The sign of the charge depends on the particle: positive charges move in the direction of current; electrons carry negative charge.

In physics, the coulomb is central to Coulomb's law, which describes the electrostatic force between point charges: F = k q1 q2 / r^2, where k = 1/(4πε0). The law underpins electrostatics, capacitance, and many electrical engineering concepts. The dimension of charge is current times time, reflecting its relation to charge transfer.

The term appears in various contexts: electrical circuits measure charge accumulation on capacitors, charge storage, and conversion between charge and electrical energy. In practical terms, calculations often use coulombs to express total charge moved or stored in a process or device, from discharging capacitors to counting electrons in nanoscale components.