In a gel electrophoresis, let's assume an SDS-PAGE, I understand that the sample is loaded on a cuboidal well and the electric field is straight downward. It is easy to assume that the sample is going to run straight in the gel. Like it does here.
But when I observed the apparatus in my lab, the anode was all throughout the base - looking something like this (cathode not shown here and the anode is insulated on the side - so effectively present at the base of the gel).
What makes the sample run in the gel only in a straight line? You may say that the forces cancel out on the either sides but what about the well that's at one end? It's being pulled downwards and also the other end.
So how does this work?