Elemental charge

Physical constant
Surname Elemental charge
Formula symbol ${\ displaystyle e}$
Size type Electric charge
value
SI 1.602 176 634e-19 C
Uncertainty  (rel.) (exactly)
Sources and Notes
Source SI value: CODATA 2018 ( direct link )

The elementary charge (symbol:) is the smallest freely existing amount of electrical charge . The charge of free particles and quantities of matter is either zero or an integer (positive or negative) multiple of . For example, the electron and the muon have the charge , a proton and a positron have the charge . The quarks of the Standard Model have charges of or , but do not occur as free particles. See the confinement phenomenon of quarks. ${\ displaystyle e}$${\ displaystyle e}$${\ displaystyle -e}$${\ displaystyle + e}$${\ displaystyle \ pm {\ tfrac {1} {3}} e}$${\ displaystyle \ pm {\ tfrac {2} {3}} e}$

The elementary charge is a natural constant . Your value is

${\ displaystyle e = 1 {,} 602 \, 176 \, 634 \ cdot 10 ^ {- 19} \, \ mathrm {C} \,}$.

This value applies exactly because the unit of measurement " Coulomb " has been defined since 2019 by assigning this value to the elementary charge. Previously, the coulomb was defined differently and was a quantity to be determined experimentally. ${\ displaystyle e}$

The value of the elementary charge is decisive for the strength of the electromagnetic interaction , see fine structure constant .

In the 19th century it was assumed that the charge has a fixed smallest unit based on electrochemical reactions. The size of the elementary charge was determined precisely for the first time by the physicist Robert Andrews Millikan with the oil droplet experiment named after him . For this work, among other things, Millikan received the Nobel Prize in 1923.

Connection with other quantities

Multiplying the elementary charge by the Avogadro constant gives the Faraday constant , which plays a role in electrochemistry .

${\ displaystyle F = N _ {\ mathrm {A}} \ cdot e \ approx 96485 \, {\ frac {\ mathrm {C}} {\ mathrm {mol}}}}$

In particle physics, the energies of particles are often given in units of electron volts (eV). An electron volt is the energy that an elementary charge (e.g. an electron) receives when it passes through an accelerating voltage of 1 volt. The conversion applies:

${\ displaystyle 1 \, \ mathrm {eV} = e \ cdot 1 \, \ mathrm {V} \ approx 1 {,} 602 \ cdot 10 ^ {- 19} \, \ mathrm {J}}$

Value in natural units

The elementary charge is not one of the constants that can be set to 1 in the natural units of particle physics . Since in this system the constant speed of light, reduced Planck's quantum of action and electrical field constant are set equal to one , and the fine structure constant as a dimensionless quantity is independent of the system of units used, the elementary charge is through ${\ displaystyle c = \ hbar = \ varepsilon _ {0} = 1}$ ${\ displaystyle \ alpha}$

${\ displaystyle \ alpha = {\ frac {e ^ {2}} {4 \ pi \ varepsilon _ {0} \ hbar c}} \ Leftrightarrow e = {\ sqrt {4 \ pi \ alpha \ varepsilon _ {0} \ hbar c}}}$

clearly determined. You then get

${\ displaystyle e = 0 {,} 302 \, 822 \, 12 \ ldots}$