1. The problem statement, all variables and given/known data Four identical parallel metal plates with area $$S$$ and distance between each two $$d$$ are located in air. The external plates are connected by wire. What is the equivalent capacitance between A and B? This is problem from Irodov. 2. Relevant equations $$q=UC$$ 3. The attempt at a solution Plates 1 and 4 are always on same potential which im not sure how to use. I tried to simplify as on the picture but that turns out to be wrong(why?).