# Electron Volt or eV | Unit of Energy

In atomic and nuclear physics electron Volt or eV is used as an unit of energy.Joule is also a unit of energy but it is very large unit while dealing with electrons in atomic and nuclear physics.
The eV energy unit is used to show the energy of smaller particles like electron.

## Derivation of electron Volt(eV)

When the voltage is applied to a electric circuit, the currentstarts flowing in the circuit according to the circuit resistance or impedance. Let the voltage applied is V and the current flowing in the circuit is I.
The power drawn by the circuit is;
P= Voltage x Current
P= V x I   ———-(1)
The current in the circuit is equal to the rate of transferring the q charges from lower to higher potential point.
I = dq/dt    ——–(2)
Putting the value of equation(2) in equation(1), we get
P= V x dq/dt    —–(3)
The energy is the capacity to do work.The energy is the power integrated over the time.
E =∫ P dt      ———–(4)
Putting the value of power Equation(3) in Equation (4), we get
E =∫ V dq/dt      ———–(4)
E = Vq    ————(5)
The chrage Q coulomb travels against an electric field of voltage V, then the work done by the charge is – QV.
If the electron crosses the electric field of 1 volt, the work done is equal to ;
E= -eV
E= -(-1.602 x 10–19 x1)
E= 1.602 x 10–19 Joules
Definition of electron Volt(eV)
One electron volt is equal to the amount of work done in bringing the one electron against the electric field having potential difference equal to 1 volt.
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