A fundamental property of matter that causes it to experience a force in an electromagnetic field.Electric charge is a fundamental property of matter that determines how it interacts with electromagnetic fields. It comes in two types, conventionally called positive and negative, with like charges repelling and opposite charges attracting. Charge is quantized — it always appears in integer multiples of the elementary charge e — and it is strictly conserved: in any closed system, the total charge never changes. This property underlies everything from the structure of atoms to the behavior of lightning and the chemistry of life.
The concept of charge was formalized by Benjamin Franklin in the 18th century, who introduced the terms positive and negative. The modern understanding of charge as a quantized, conserved quantity emerged with experiments by Robert Millikan (1909) and the development of quantum electrodynamics in the mid-20th century.
Charge creates and responds to electric and magnetic fields. A charged particle produces an electric field that exerts forces on other charges, and when it moves, it also generates a magnetic field. The strength of these interactions is set by the fine-structure constant, about 1/137. In quantum electrodynamics, charge is the coupling constant that determines how often a particle emits or absorbs a photon, the carrier of the electromagnetic force.
Electric charge is the basis of all electrical technology: from power generation and electronics to medical imaging like MRI and particle accelerators used in cancer therapy.
The electric charge of a single electron is exactly equal in magnitude to that of a proton, but opposite in sign — a balance that, if off by even a tiny fraction, would make atoms unstable and matter as we know it impossible.
| \Delta Q | variable | Accumulated charge change in the superconductor — electric charge coulomb |
| \Delta \Phi | variable | Change in magnetic flux through the superconducting loop — magnetic flux weber |
| \nu | variable | Filling factor (integer or fractional) of the quantum Hall state — dimensionless |
| e | constant | Magnitude of the electric charge of a single electron or proton — elementary charge = 1.602176634e-19 coulomb |
| \Phi_0 | constant | Superconducting flux quantum, h/(2e), the fundamental unit of magnetic flux in a superconductor — magnetic flux quantum = 2.067833848e-15 weber |
| Q | variable | Electric charge of the body — electric charge coulomb |
| M | variable | Mass of the body — mass kilogram |
| k_e | constant | Electrostatic force constant in Coulomb's law — coulomb constant = 8.9875517923e9 newton metre squared per coulomb squared |
| G | constant | Newtonian constant of gravitation — gravitational constant = 6.67430e-11 cubic metre per kilogram per second squared |
| r_± | variable | Inner and outer event horizon radii — horizon radius metre |
| Q | variable | Electric charge of the black hole — electric charge coulomb |
| M | variable | Mass of the black hole — mass kilogram |
| G | constant | Newtonian constant of gravitation — gravitational constant = 6.67430e-11 cubic metre per kilogram per second squared |
| c | constant | Speed of light in vacuum — speed of light = 299792458 metre per second |
| k_e | constant | Electrostatic force constant in Coulomb's law — coulomb constant = 8.9875517923e9 newton metre squared per coulomb squared |
| p_max | variable | maximum momentum — momentum kilogram metre per second |
| e | variable | electric charge — electric charge coulomb |
| B | variable | magnetic field strength — magnetic field tesla |
| L | variable | characteristic length scale — length metre |
| c | constant | speed of light in vacuum — speed of light = 299792458 metre per second |
| \omega_p | variable | plasma angular frequency — angular frequency radian per second |
| n | variable | electron number density — number density per cubic metre |
| e | variable | elementary charge — electric charge coulomb |
| m | variable | electron mass — mass kilogram |
| \epsilon_0 | constant | permittivity of free space — vacuum permittivity = 8.8541878128e-12 farad per metre |
| \sqrt{} | operator | takes the square root — square root |
| σ_H | variable | Hall conductivity — electrical conductivity siemens |
| ν | variable | Filling factor (integer or fractional) — filling factor |
| e | variable | Elementary charge — electric charge coulomb |
| h | variable | Planck constant — planck constant joule second |
