A capacitor is a device that stores electric energy in an electric field form. A capacitor consists of two conductors separated by a small distance. When the conductors are connected to a charging device (for example, a battery), the charge is transferred from one conductor to the other until the difference in potential between the conductors becomes equal to the potential difference between the terminals of the charging device. The amount of charge stored on either conductor is directly proportional to the voltage, and the constant of proportionality is known as the capacitance.