ms illustrating equivalent circuits of the variable capacitor;FIGS. 11A and 11B are diagrams illustrating equivalent circuits of the variable capacitor;FIGS. 12A and 12B are a plan view and a cross sectional view, respectively, of an example of a variable capacitor according to a fourth embodiment;FIGS. 13A and 13B are cross sectional views of the variable capacitor illustrated in FIGS. 12A and 12