What is "electronvolt"

n. (context physics English) (alternative spelling of electron volt English)

In physics, the electronvolt (symbol eV, also written electron volt) is a unit of energy equal to approximately 160 zeptojoules (10 joules, symbol zJ) or joules (symbol J). By definition, it is the amount of energy gained (or lost) by the charge of a single electron moving across an electric potential difference of one volt. Thus it is 1 volt (1 joule per coulomb, ) multiplied by the elementary charge (e, or ). Therefore, one electronvolt is equal to Historically, the electronvolt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences because a particle with charge q has an energy after passing through the potential V; if q is quoted in integer units of the elementary charge and the terminal bias in volts, one gets an energy in eV.

[[ spectrum.svg|right|frame|Photon frequency vs. energy particle in electronvolts. The energy of a photon varies only with the frequency of the photon, related by speed of light constant. This contrasts with a massive particle of which the energy depends on its velocity and rest mass.

Legend

γ: Gamma rays

|MIR: Mid infrared

|HF: High freq.

HX: Hard X-rays

FIR: Far infrared

MF: Medium freq.

SX: Soft X-rays

Radio waves

LF: Low freq.

EUV: Extreme ultraviolet

EHF: Extremely high freq.

VLF: Very low freq.

NUV: Near ultraviolet

SHF: Super high freq.

VF/ULF: Voice freq.

Visible light

UHF: Ultra high freq.

SLF: Super low freq.

NIR: Near Infrared

VHF: Very high freq.

ELF: Extremely low freq.

Freq: Frequency

]]

The electronvolt is not an SI unit, and its definition is empirical (unlike the litre, the light year and other such non-SI units), thus its value in SI units must be obtained experimentally. Like the elementary charge on which it is based, it is not an independent quantity but is equal to . It is a common unit of energy within physics, widely used in solid state, atomic, nuclear, and particle physics. It is commonly used with the metric prefixes milli-, kilo-, mega-, giga-, tera-, peta- or exa- (meV, keV, MeV, GeV, TeV, PeV and EeV respectively). Thus meV stands for milli-electronvolt.

In some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion electronvolts; it is equivalent to the GeV.

Measurement

Unit

SI value of unit

Energy

eV

Mass

eV/c

Momentum

eV/c

Temperature

eV/k

Time

ħ/eV

Distance

ħc/eV