In its simplest form, the capacitor is a set of oppositely charged parallel plates separated by a distance (d). From the equation for the potential difference of parallel plates and the definition of capacitance, the capacitance for parallel plates is
Strictly speaking, this equation is valid only when there is a vacuum between the plates.
When a nonconducting material is placed between the capacitor plates, more charge can be stored because of the induced charge on the surface of the electrical insulator. The ratio of the capacitance with the insulator to the vacuum capacitance is called the dielectric constant (κ, the Greek letter kappa). The values for the dielectric constants can be found in tables of properties of materials. The equation for the parallel plate capacitor with a dielectric that fills the space between the plates is
The energy stored in a capacitor can be found by any of the following three equations, which are each in terms of different variables:
Capacitors can be connected either in parallel or in series. Two capacitors are in parallel if the negative plates are connected and the positive plates are connected, as shown in Figure 1.