Electric charge

Charge is the fundamental property that makes electricity possible. It comes in two flavours: positive (carried by protons) and negative (carried by electrons). One golden rule governs how they interact: like charges repel, opposite charges attract.

Rubbing a balloon can charge it. Near a neutral wall, its field redistributes charge slightly: the nearer induced opposite charge attracts the balloon. Two similarly charged balloons repel. Electric attraction also helps bind electrons to nuclei, although atoms require a quantum description.

Charge is measured in coulombs (C). One coulomb is an enormous pile of electrons — about 6.24 × 10¹⁸ of them. This connects directly to current: when one coulomb of charge flows past a point every second, that is exactly one amp.