Electric charge - Aetherwisp

Electric charge, often simply just charge, is the physical property of a particle that causes it exhibit electromagnetic interaction. It may be positive, negative or zero. A particle with zero electric charge is said to be electrically neutral. Charges of different type annihilate each other, in the sense that their effects cancel each other out. Charge is quantized and the fundamental unit of charge is the charge of the electron $e$ .

The SI unit of charge is the Coulomb $\text{C}$ .

Conservation#

Charge is a conserved quantity. It cannot be created or destroyed. The net total charge in the Universe is constant. This fact is called global conservation of charge. Another, more strict, phenomenon is local conservation of charge, which means that if a charge were to move from place A to place B, it must follow a continuous path in between the two. This means that a charge cannot simply vanish alongside an equal and opposite charge on the other side of the Galaxy, despite global conservation allowing that. The two charges must "touch" in order to annihilate.

The mathematical statement of local conservation of charge is given by comparing the time variation of the volume charge density $\rho$ with the electric current density $\mathbf{J}$ :

\frac{ \partial \rho }{ \partial t } =-\nabla\cdot \mathbf{J}