Voltage is a measure of electromotive force, but it is measured by how much work a charge can do as it flows between two points.
Say I seperate some amount of positive and negative charge and in doing so create a voltage. Now let's say I seperate the same amount of positive. and neg. charge but move the two farther apart. In the second case, the voltage should be the same since I've increased the distance between the charges but decreased the force acting on them so the amount of work the charge can do has stayed the same.
Now I have two cases where the voltage between two points is the same, but the Electromotive force is different.
How can this be? Did I make incorrect assumptions? Does this mean potential difference is not really a measure of emf.