In this section we will investigate resonance in radio reception. Although studying electrical circuits requires different terminology, and despite the fact that the scale of our investigations will shrink to that of moving electrical charges, resonance in a spring and mass system provides an analogy for what will be encountered here. The electromagnetic waves from a transmitting station will resonate with an electrical circuit in a radio and the efficient transfer of energy at resonance will result in music or speech. We will set up a resonant circuit by designing and building a simple AM radio receiver. The frequency of a common electrical resonant circuit depends on the value of only two components, the capacitor and the inductor .
Capacitance is the term used to define the ability to store electrical energy in conducting plates.
A capacitor is composed of two conducting plates, such as two sheets of metal foil, separated by a insulator, or dielectric. The insulator can be paper, oil, mica, ceramic, plastic film, or even air. When a capacitor is connected to a voltage source, electrons from one conductor or plate are attracted to the positive terminal of the battery, while an equal number of electrons is supplied to the other plate by the voltage source. The current in this circuit will continue only until the capacitor is charged to the potential equal to that of the voltage source. Figure 9 .