So let's suppose we take a gel. We take the gel, we place the gel into a special apparatus, and we create a PH gradient. What that means is on one side, let's say on the left side of our gel, we're going to have a low PH acidic environment. On the other end, on the right side, we're going to have a high PH, a basic environment. Now, we're also going to connect both ends of that gel to a voltage source. We're going to create an electric potential difference between the two sides, and that will create an electric field.