Voltage is the work done per unit charge. Given by:
V = W/q
Electron volt is the maximum kinetic energy gained by the electron in falling through a potential difference of 1 volt. Given by:
K.E (max) = eV
When there is a potential difference (voltage) of 10V between two points, it means that we are doing 10 joules of work per unit charge (electron).
My question is that if we are doing 10 joules of work on an electron than why isn't the kinetic energy of electron equal to 10 joules? Why do we multiply charge of electron with Voltage to get the kinetic energy gained by the electron?