Question
Explain and define the electronvolt. $\text{OR}$ What is electronvolt?
✓
Answer
When an electric charge moves under the influence of an electric field, the work done by the field on the charge increases the kinetic energy of the charge as the electric force is a conservative force. Since the elementary charge e is widely encountered in atomic and nuclear physics, a convenient non$-SI$ unit of energy used is the electronvolt.
Definition ; An electronvolt $($symbol, $eV)$ is the increase in the kinetic energy of a particle with a charge equal in magnitude to the elementary charge e when the particle is accelerated through a potential difference of one volt.
$\Delta(K E)=q A V$
where $q$ is the charge and $\Delta V$ is the potential difference.
$\therefore 1 eV = e (1 V )$
$=\left(1.602 \times 10^{-19} C \right)(1 J / C )$
$=1.602 \times 10^{-19} J$
$[$Notes: $(1) SI$ prefixes are commonly used with the unit.
Therefore, $1 keV =10^3$ $eV =1.602 \times 10^{-16} J , 1 MeV =10^6 eV =1.602 \times 10^{-13} J$, etc.
$(2)$ In practice, it is not unusual to use the electronvolt as an energy unit in nonelectrical situations.
For example, an air molecule at room temperature has a kinetic energy of about $\frac{1}{40} eV$,
the electron mass is $511 keV / c _0{ }^2$, and the proton mass is $938 MeV / c _0{ }^2$,
where $c_0$ is the speed of light in free space.$]$
Definition ; An electronvolt $($symbol, $eV)$ is the increase in the kinetic energy of a particle with a charge equal in magnitude to the elementary charge e when the particle is accelerated through a potential difference of one volt.
$\Delta(K E)=q A V$
where $q$ is the charge and $\Delta V$ is the potential difference.
$\therefore 1 eV = e (1 V )$
$=\left(1.602 \times 10^{-19} C \right)(1 J / C )$
$=1.602 \times 10^{-19} J$
$[$Notes: $(1) SI$ prefixes are commonly used with the unit.
Therefore, $1 keV =10^3$ $eV =1.602 \times 10^{-16} J , 1 MeV =10^6 eV =1.602 \times 10^{-13} J$, etc.
$(2)$ In practice, it is not unusual to use the electronvolt as an energy unit in nonelectrical situations.
For example, an air molecule at room temperature has a kinetic energy of about $\frac{1}{40} eV$,
the electron mass is $511 keV / c _0{ }^2$, and the proton mass is $938 MeV / c _0{ }^2$,
where $c_0$ is the speed of light in free space.$]$
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