Two capacitors are identical, except that one is empty and the other is filled with a dielectric ( k= 5.00). The empty capacitor is connected to a 6.0 V battery. What must be the potential difference across the plates of the capacitor filled with a dielectric such that it stores the same amount of electrical energy as the empty capacitor? So here are my thoughts so far..... V= 6 V Energy=.5CV^2 So the energy of the empty capacitor is .5V^2 which is .5(18^2)=18 right????? they give no value for C so i assume it is one??? I have no idea where k comes into the picture. please help. thanks.