Let's begin by assuming that the cell is only permeable to our potassium. So as potassium leaves the cell, it travels from the inside to the outside via these proteins that passively diffuse our molecules, our ions. So as our potassium leaves the cell, we have less positively charged ions. And so the positive charge will decrease and the inside will become more negative. At the same time as these potassiums are being pumped into the outside, the outside will gain a certain positive charge. So as the positive charge builds up on the outside, the electric force begins to force the potassium back inside.