We know that V= W / Q where Vis the potential difference between two points in an electrical circuit and W is the work done while moving Q coulomb of positive charge from one point to another. Hence, when W = 1 J and Q = 1 coulomb, then V= 1 volt. So, 1 volt is the potential difference between the two points if 1 J of work has to be done for moving 1 coulomb of positive charge between those two points.