A capacitor is a device that is used to store charges in an electrical circuit. A capacitor works on the principle that the capacitance of a conductor increases appreciably when an earthed conductor is brought near it. Hence, a capacitor has two plates separated by a distance having equal and opposite charges. The space between the conductors may be filled by vacuum or with an insulating material known as a dielectric. The ability of the capacitor to store charges is known as capacitance.
Working principle of a capacitor
Let us consider the parallel plate capacitor. It consists of two parallel plates separated by a dielectric. When we connect a DC voltage source across the capacitor, one plate is connected to the positive end and the other plate to the negative end. When the potential of the battery is applied across the capacitor, plate I become positive with respect to plate II.
Across the capacitor, an electric field appears. The positive plate will collect positive charges from the battery, while the negative plate will collect negative charges. After a certain stage, the capacitor’s capacitance with respect to this voltage allows it to hold the maximum amount of charge. This time span is called the charging time of the capacitor.
When the battery is removed from the capacitor, the two plates hold a negative and positive charge for a certain time. Thus, the capacitor acts as a source of electrical energy. If these plates are connected to a load, the current flows to the load from Plate I to Plate II until all the charges are dissipated from both plates. This time span is known as the discharging time of the capacitor.