unit of energy

The electron-volt or electron volt, symbol eV, is used to measure energy. It is defined as the amount of energy an electron gains after being accelerated by 1 volt of electricity. Joules are used often for energy measurement, but it is sometimes useful to use electron-volts for very small amounts of energy, such as that carried by a single subatomic particle. To convert joules into electron-volts, divide joules by the charge of an electron, which is about 1.602×10−19 coulomb.

E.g. 5 J = 5/1.602×10−19
5 J = 3.121×10+19 eV.

The electronvolt is often used in atomic, nuclear and particle physics. For example, the energy of photons can be measured by the voltage necessary to overcome their photoelectric effect.

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