After advanced mathematical deduction, the magnetic field energy stored in the coil is as follows: when there is current in the coil, the magnetic field energy will be stored in the coil, and the greater the current passing through the coil, the more energy will be stored; In a coil with the same current, the greater the inductance, the more energy is stored, so the inductance of the coil also reflects its ability to store magnetic energy. Compared with electric field energy, magnetic field energy has many similar characteristics: (1) The transformation of magnetic field energy and electric field energy in the circuit is reversible. For example, with the increase of current, the magnetic field of the coil increases, and the stored magnetic field energy increases; With the decrease of current, the magnetic field weakens, and the magnetic field energy is converted into electrical energy through electromagnetic induction. So the coil, like the capacitor, is an energy storage element, not a resistive energy dissipation element. (2) The calculation formula of magnetic field energy is the same as that of electric field energy in form.