Acertain amount of energy must be used in the form of work to overcome the forces and move the charges a given distance apart. All opposite charges possess a certain potential energy because of the separation between them. The difference in potential energy of the charges is voltage. Voltage, symbolized byV, is the driving force in electric circuits and is what establishes current. The unit of voltage is the volt. Voltage provides energy to electrons or ions that allows them to move through a circuit. This movement is electrical current characterized by I, which results in work being done in an electric circuit. The measurement unit of current is ampere.