In physics, the electronvolt (symbol eV, also written electron volt) is a unit of energy equal to approximately 160 zeptojoules (10−21 joules, symbol zJ) or 1.6×10−19 joules (symbol J). By definition, it is the amount of energy gained (or lost) by the charge of a single electron moving across an electric potential difference of one volt. Thus it is 1 volt (1 joule per coulomb, 1 J/C) multiplied by the elementary charge (e, or 1.6021766208(98)×10−19 C). Therefore, one electronvolt is equal to 1.6021766208(98)×10−19 J. Historically, the electronvolt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences because a particle with charge q has an energy E = qV after passing through the potential V; if q is quoted in integer units of the el