Table of Contents
What Is an Electron Volt?
An electron volt (eV) is a unit of energy equal to the kinetic energy gained by a single electron accelerated through an electric potential difference of one volt. It equals approximately 1.602 x 10^-19 joules. Despite its name, it is a unit of energy, not voltage.
The eV is commonly used in atomic physics, nuclear physics, and particle physics because the energies involved are extremely small when expressed in joules. For example, the energy to ionize a hydrogen atom is 13.6 eV, far more convenient than writing 2.18 x 10^-18 J.
Conversion Formula
Energy Scale
| Energy | eV | Context |
|---|---|---|
| Thermal (room temp) | 0.025 | kT at 300K |
| Visible light photon | 1.6-3.3 | Red to violet |
| Hydrogen ionization | 13.6 | Ground state |
| X-ray photon | 100-100,000 | Medical imaging |
| Proton rest mass | 938.3 MeV | E=mc² |
Frequently Asked Questions
Why use eV instead of Joules?
Joules are too large for atomic-scale energies. Writing 13.6 eV is much more practical than 2.18 x 10^-18 J. The eV provides a natural scale for processes involving single charged particles.
Can eV measure mass?
Yes, through E=mc^2. Particle physicists express mass in eV/c^2 or equivalently MeV/c^2 and GeV/c^2. The electron mass is 0.511 MeV/c^2.
What is a keV, MeV, GeV?
These are kilo-, mega-, and giga-electron volts: 10^3, 10^6, and 10^9 eV respectively. X-rays are measured in keV, nuclear reactions in MeV, and particle colliders in GeV or TeV.