4. A parallel-plate capacitor with C = 13.5 pF is charged to a voltage of V = 12.5 V. Then the battery is disconnected and a porcelain slab (k = 6.5) is inserted between the plates. a. What is the stored potential energy before the slab is inserted? 열다2 US (135)(12.5) b. What is the stored potential energy after the slab is inserted? Сани к собе c. How do you account for the difference? words Корей