<P> In physics, the electronvolt (symbol eV, also written electron - volt and electron volt) is a unit of energy equal to approximately 1.6 × 10 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 6981160217662079999 ♠ 1.602 176 6208 (98) × 10 C). Therefore, one electronvolt is equal to 6981160217662079999 ♠ 1.602 176 6208 (98) × 10 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 elementary charge and the terminal bias in volts, one gets an energy in eV . </P> <P> The electronvolt is not a SI unit, and its definition is empirical (unlike the litre, the light - year and other such non-SI units), thus its value in SI units must be obtained experimentally . Like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J / C √ 2 h α / μ c . It is a common unit of energy within physics, widely used in solid state, atomic, nuclear, and particle physics . It is commonly used with the metric prefixes milli -, kilo -, mega -, giga -, tera -, peta - or exa - (meV, keV, MeV, GeV, TeV, PeV and EeV respectively). Thus meV stands for milli - electronvolt . </P>

I joule is equal to how many ev
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