If the potential difference between point A and point B is 10 Volts, then when a unit positive charge passes from A to B, the charge loses 10 J of energy. But when an electron passes from A to B does it gain energy, because in W = Q . V , Q is negative. I am really confused in potential difference and in the formula W = Q . V. I have seen in some books that when electron is said in the question the calculation use the value of positive elementary charge, why is it so?