A cylindrical capacitor is made of two thin-walled concentric cylinders. The inner cylinder has radius 8mm , and the outer one a radius 12mm . The common length of the cylinders is 159m . What is the potential energy stored in this capacitor when a potential difference 5V is applied between the inner and outer cylinder? (k =1/4∗π∗ϵ0=8.99×109N⋅m2/C2)