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The definition of electronvolt (eV) from wiki is

In physics, the electronvolt (symbol eV; also written electron volt) is a unit of energy equal to approximately 160 zeptojoules (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 moved across an electric potential difference of one volt.

Masses of particles are often expressed in eV. But to say that the energy or mass of a particle such as a neutrino is measured in eV is weird to me since it cannot be accelerated by an electric field. Why do people use the electronvolt to describe the masses of all particle, even those that don't carry electric charges?

innisfree
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user6760
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2 Answers2

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One electron-volt $=1.6 \times 10^{-19} joules$ and is a unit of energy that is equal to the energy acquired by an electron falling across a 1 volt potential difference. The particle (neutrino) doesn't need a charge to have some energy. Instead of expressing the mass of a particle in kg, we can express it as $mc^2$ which is an energy (joules or eV... your choice). This makes it easy to calculate the total energy of a particle $E_{Total}=T_{KineticEnergy}+mc^2$ since all the quantities are now energies.

Gary Godfrey
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Although the eV is defined with respect to a particle of unit charge (an electron) in an electric field, it is simply a unit of energy.

There are simple relations between thr eV and everyday units of energy, such as the Joule or calorie.

Thus energies of all sorts of things, in fact any energy, can be expressed in eV, even if it has nothing whatsoever to do with electric charge or electric fields. With that in mind, the energy and mass (by mass-energy equivalence) of neutral particles, such as the neutrino, may be expressed in eV without any contradiction.

innisfree
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