Figure 3.23

3.16   A cubical box (sides of length a) consists of five metal plates, which are welded together and grounded (Fig 3.23). The top is made of a separate sheet of medal, insulated from the others, and held at a constant potential V_o. Find the potential inside the box. [What should the potential be at the center (a/2, a/2, a/2) be? Check numerically that your formula is consistent with this value.]