Electron volt or eV
The concept of electron volt is very simple. Let us start from very basic. We know the unit of power is watt.W = VI, where V is the voltage and I is the current. Now as I is current, it is nothing but rate of charge transfer. Therefore, instantaneous impression of power would be Where, q(t) is the amount of charge transferred in time t.
Now energy is expressed as Where, q is the charge in Coulomb crosses a voltage V volts.
From the expression of energy we can write the energy required or work to be done for crossing an electric field of total voltage V by a charge Q coulomb is QV coulomb - volt or joules. Now we know the charge of an electron is - 1.6 × 10-19 coulomb and consider it has crossed an electric field of total voltage 1 V. Then the total work to be done is charge of electron × 1 V. This amount of energy is considered as a micro unit of energy called electron-volt.