unit:EV
An electron volt (eV) is the energy that an electron gains when it travels through a potential of one volt. You can imagine that the electron starts at the negative plate of a parallel plate capacitor and accelerates to the positive plate, which is at one volt higher potential. Numerically $1 eV$ approximates $1.6x10^{-19} joules$, where $1 joule$ is $6.2x10^{18} eV$. For example, it would take $6.2x10^{20} eV/sec$ to light a 100 watt light bulb.