English: An AC equivalent circuit of the secondary coil of a Tesla coil, showing the effect of stray capacitance. The secondary of a Tesla coil consists of a long coil with many turns of fine wire, connected to ground at one end and to a smooth metal toroidal-shaped capacitive electrode (disk, top) at the other. Although there is no capacitor, the secondary coil acts like a tuned circuit, resonating with the stray parasitic capacitance in the circuit. This equivalent circuit shows these capacitances. The capacitor on the right represents the capacitance between the toroid electrode and ground. The capacitors on the left represent the capacitance between the windings of the secondary coil.