A variable capacitor allows for a range of capacitance. Variable capacitors are designed so that capacitance can be changed through a mechanical means. Variable capacitors are used when the application requires an adjustment of capacitance such as in a radio tuner.

Click on the slider to adjust the capacitor

The tutorial is based on a typical variable capacitor that consists of two sets of plates. One set is called the rotor and the other the stator. The rotor is connected to the adjustment knob outside the capacitor. The two sets of plates are close together but not touching. Air is the dielectric in a variable capacitor. As the capacitor is adjusted, the sets of plates become more or less meshed, increasing or decreasing the area of overlap between the plates. As the plates become more meshed, capacitance increases. As the plates become less meshed, capacitance decreases.