Electronvolt

Einstein-triangle-in-natural-units

Colors in eV

EV to nm vis-en

Light spectrum

Electronvolt (eV) is a unit of energy used in physics, specifically in the fields of particle physics and condensed matter physics. It is defined as the amount of energy gained (or lost) by a single electron accelerating through an electric potential difference of one volt. Thus, one electronvolt is equal to 1.602176634 × 10⁻¹⁹ joules. The electronvolt is a convenient unit for expressing energy levels in atomic, molecular, and nuclear processes because these energies are typically within the range of a few eV to several hundred keV (kilo-electronvolts) or even MeV (mega-electronvolts) for nuclear processes.

Definition

The electronvolt is not part of the International System of Units (SI), but it is accepted for use with the SI. The energy E in electronvolts is calculated as the product of the charge of an electron (e, approximately 1.602 × 10⁻¹⁹ coulombs) and the potential difference V in volts, i.e., E(eV) = eV. This relationship makes the electronvolt a natural unit of energy for expressing the outcome of experiments involving electrically charged particles.

Usage

Electronvolts are widely used in the field of high-energy physics, nuclear physics, and condensed matter physics, as well as in various branches of astronomy and astrophysics. In high-energy physics, particle masses are often expressed in terms of eV/c² (using Einstein's equation E=mc²), where c is the speed of light in a vacuum. This practice simplifies the comparison of particle masses since the mass of a particle is directly related to its energy.

In condensed matter physics, the electronvolt is used to express the energy levels of electrons in solids, including the energy required to excite an electron from the valence band to the conduction band in a semiconductor. It is also used to describe the energy of photons in the context of photoelectric effect and other phenomena.

Multiples

The electronvolt has several commonly used multiples, including: - The kilo-electronvolt (keV), equal to 1,000 eV - The mega-electronvolt (MeV), equal to 1,000,000 eV - The giga-electronvolt (GeV), equal to 1,000,000,000 eV - The tera-electronvolt (TeV), equal to 1,000,000,000,000 eV

These multiples are particularly useful in high-energy physics, where particle accelerators can accelerate particles to energies of several TeV.

Relation to Other Units

While the electronvolt is a unit of energy, it can also be related to other physical quantities through fundamental physical constants. For example, in particle physics, the mass of particles is often given in eV/c², linking energy to mass. Additionally, the temperature of a system can be expressed in electronvolts, using the Boltzmann constant (k_B), where 1 eV corresponds to approximately 11,605 K.

Conclusion

The electronvolt is a crucial unit of energy in the study of subatomic particles, nuclear reactions, and the properties of solids. Its convenience for expressing very small amounts of energy and its direct relationship to electric charge make it an indispensable unit in the toolkit of physicists and engineers alike.

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