A battery is an electron pump that moves from the negative terminal to the terminal. However physicists always regard electric current as , which means that the current flows from to , even though in reality positives don't move.

For a circuit to work, there has to be a source of . The circuit has to be complete and made of materials.

In circuits, the components are in a line so that the current passes from one component to another in turn. In parallel circuits the components each have their own , and an electron passes through one or the other. The total current is the of the currents in each branch.

Current is measured with an wired in with the component. difference is measured with a wired in with the component.