electronvolt

electronvolt

Non-SI unit accepted for use with SI
Name Symbol Quantity Value in SI units
electronvolt eV energy 1.602 176 634 × 10−19 J

Definition

The electronvolt, symbol eV, is a non-SI unit of energy accepted for use with the SI.

One electronvolt is equal to the kinetic energy acquired by one electron in passing through a potential difference of one volt in vacuum.

The value of one electronvolt in terms of joules is found by multiplying the magnitude of the charge carried by one electron, expressed in coulombs, by one volt.

The magnitude of the charge on one electron is equal to the elementary charge, e, which is defined as 1.602 176 634 × 10−19 C. Therefore, 1 eV = 1.602 176 634 × 10−19 J.

The electronvolt is often combined with the SI prefixes, and is typically used to measure the energies of elementary particles.

Unit of mass

Since mass is related to energy through Einstein’s mass-energy equivalence equation, E = mc2, the masses of elementary particles can be expressed in terms of electronvolts, and c, where c is the speed of light in vacuum.

1 \mspace{4mu} \text{eV}/c^2 \mspace{18mu} = \mspace{4mu} \dfrac{1.602\ 176\ 634 \times 10^{-19}} {(299\ 792\ 458)^2} \mspace{6mu} \text{kg}\\ \\ \\ 1 \mspace{4mu} \text{eV}/c^2 \mspace{19mu} = \mspace{4mu} 1.782\ 661\ 921\ 627... \times 10^{-36} \mspace{6mu} \text{kg}\\ \\ 1 \mspace{4mu} \text{MeV}/c^2 \mspace{4mu} = \mspace{4mu} 1.782\ 661\ 921\ 627... \times 10^{-30} \mspace{6mu} \text{kg}\\ \\ 1 \mspace{4mu} \text{GeV}/c^2 \mspace{6mu} = \mspace{4mu} 1.782\ 661\ 921\ 627... \times 10^{-27} \mspace{6mu} \text{kg}

Examples of masses of elementary particles

Quarks
Name Mass in MeV/c2 Mass in SI units
up 2.2 3.92 × 10−30 kg
down 4.6 8.2 × 10−30 kg
charm 1 280 2.28 × 10−27 kg
strange 96 1.71 × 10−28 kg
top 173 100 3.086 × 10−25 kg
bottom 4 180 7.45 × 10−27 kg
Leptons
Name Mass in MeV/c2 Mass in SI units
electron 0.511 9.109 × 10−31 kg
muon 105.658 1.883 52 × 10−28 kg
tau 1 776.86 3.167 54 × 10−27 kg
Bosons
Name Mass in GeV/c2 Mass in SI units
W boson 80.385 1.432 992 × 10−25 kg
Z boson 91.1875 1.625 565 × 10−25 kg
Higgs boson 125.09 2.229 932 × 10−25 kg