A pair of AA cells. The + sign indicates the polarity of the potential distinction between the battery terminals. The electric potential at any point is characterized as the vitality required to bring a unit test charge from a boundless distance gradually to that point. It is usually measured in volts, and one volt is the potential for which one joule of work must be exhausted to bring a charge of one coulomb from infinity. This meaning of potential, while formal, has minimal practical application, and a more valuable idea is that of electric potential contrast, and is the vitality required to move a unit charge between two determined points. The volt is so unequivocally recognized as the unit of decision for measurement and depiction of electric potential distinction that the term voltage sees greater everyday usage.
The idea of electric potential is firmly connected to that of the electric field. A small charge placed inside an electric field encounters a force, and to have carried that charge to that point against the force requires work. An electric field has the special property that it is conservative, which means that the path taken by the test charge is irrelevant: all paths between two determined points exhaust the same vitality, and in this way a one of a kind value for potential contrast may be stated. For practical purposes, it is valuable to characterize a typical reference point to which potentials may be communicated and compared. While this could be at interminability, a significantly more helpful reference is the Earth itself, which is assumed to be at the same potential all over the place. This reference point naturally takes the name earth or ground. Earth is assumed to be a limitless wellspring of equal amounts of positive and negative charge, and is therefore electrically uncharged and unchargeable.