What is the ratio of the electric energy that can be stored in a capacitor to the magnetic energy that can be stored in an inductor of the same size (i. e., the same volume). For the capacitor, assume that air is between the plates; the maximum electric field is then the breakdown strength of air, about 3.00 MV/m. The maximum magnetic field attainable in an ordinary solenoid with an air core is on the order of 10 T.