Electric charge and current

Electric charge comes in exactly two flavours, positive and negative, and like charges repel while opposite charges attract. Nearly everything you see charged up in daily life — a balloon rubbed on hair, a phone battery, a lightning bolt — comes down to an imbalance between these two.

An electric current is simply charge on the move: a steady flow of charge through a conductor, measured in amperes as the amount of charge passing a point each second. In most everyday circuits it's electrons doing the moving, drifting slowly through the wire's atomic lattice.

Current doesn't get "used up" as it flows around a circuit, even though components along the way certainly use up energy. Measure the current before a resistor and after it, in a simple series circuit, and you'll get the same number both times — what changes across the resistor is voltage, not current.