Benjamin Franklin was the first to name the two types of charges, calling one positive and the other negative. He also established the convention that the charge that moves is associated with electrons, and that it has a negative sign. He assumed that electricity flows from positively charged to negatively charged regions.
Electric current is composed of moving charges. In metals, it is the free electrons that move, so the current is negative. In semiconductors, currents may be either positive or negative, due to the movement of holes and free electrons. Electric potential is a voltage. Charges flow when there is a potential difference applied between two different points. This potential difference creates a pressure that causes the charges to move, just like a pump does water. Potential differences are created from power sources such as batteries or generators, and are measured in units called volts. Volts are named after Italian physicist Alessandro Volta.
Current is measured in amperes or amps, for short. It is named after the French physicist Andre Marie Ampere. An ampere is equal to one coulomb of charge per second, which is in magnitude a billion billion of electrons. The coulomb is named after another French physicist, Charles Coulomb.
