English chemist and physicist Michael Faraday (1791-1867) developed the first scientific understanding of fundamental relations in electrochemical processes. He discovered that the amount of a substance produced or consumed in an electrochemical process depends quantitatively on the amount of electricity that flows as the reaction takes place. For example, the thickness of the silver plate that is deposited electrochemically on a spoon is greater if the electrical current is allowed to flow longer.

Just as the amount of water flowing through a pipe is equal to the rate of flow, or the current, multiplied by the length of time that the water flows, the amount of electricity that passes through a wire is equal to the electrical current multiplied by the time. The unit for current flow is the ampere. One ampere or amp is equivalent to one coulomb per second; a coulomb is the measure...