A parallel-plate capacitor with plates of area \(A\) separated by a distance \(d\) in vacuum is charged to an initial potential difference \(\Delta V_0\) and then disconnected from the charging source. An uncharged conducting slab of thickness \(t\) (where \(t < d\)) and area \(A\) is then inserted between the plates parallel to them, without touching either plate. Which of the following expressions correctly represents the new electric potential difference \(\Delta V\) between the capacitor plates?