So we build up our positive charge on the outside, and that drives via an electric force, these potassiums slowly back inside. And eventually when the electric force, due to the positive charge build up on the outside is exactly the same as the force that is pushing our potassiums to the outside. As a result of the concentration gradient, when these two forces are exactly the same and point in the opposite direction, equilibrium is reached. And when equilibrium is reached, we have this concentration of our potassium. So let's try to use this concentration and the nursed equation to calculate what the voltage difference is. So remember when we discussed the chemistry of neurons?