An uncharged capacitor is charged by moving some electrons from one plate of the capacitor to the other plate.
(a) Is the mass of the charged capacitor greater than, less than, or the same as the mass of the uncharged capacitor?
(b) Choose the best explanation from among the following:
I. The charged capacitor has more mass because it is storing energy within it, just like a compressed spring.
II. The charged capacitor has less mass because some of its mass now appears as the energy of the electric field between its plates.
III. The capacitor has the same mass whether it is charged or not because charging it only involves moving electrons from one plate to the other without changing the total number of electrons?