A capacitor stores electrical energy. It is charged by hooking into an electrical circuit. When the capacitor is fully charged a switch is opened and the electrical energy is stored until it is needed. When the energy is needed, the switch is closed and a burst of electrical energy is released.
A capacitor consists of two electrical conductors that are not in contact. The conductors are usually separated by a layer of insulating material, dielectric. The dielectric is not essential but it keeps the conductors from touching. When the capacitor is hooked into an electric circuit with a current, one conductor becomes positively charged and the other negative. The conductors are not in contact, so the current cannot flow across the capacitor. The capacitor is now charged up and the switch can be opened. The capacitor is storing electrical energy. When the energy is needed the capacitor is connected to the circuit needing the energy. The current flows rapidly in the opposite direction, discharging the capacitor in a burst of electrical energy.
Capacitors take many shapes, but the simplest is a parallel plate capacitor. It consists of two flat conductors placed parallel to each other. Larger plates can store more charge and hence more energy. Putting the plates close together also allows the capacitor to store more energy. The capacitance of a capacitor is the charge on the conductor divided by the voltage and is used to measure the ability of a capacitor to store energy. The capacitance of a parallel plate capacitor is proportional to the area of the plates divided by the distance between them. This number must then be multiplied by a constant which is a property of the dielectric between the plates. The dielectric has the effect of increasing the capacitance.
Capacitors come in a wide range of sizes. Banks of large capacitors can store and rapidly release large bursts of electrical energy. Among other uses, engineers can use such devices to test a circuit's performance when struck by a bolt of lightning. On an intermediate scale, a camera flash works by storing energy in a capacitor and then releasing it to cause a quick bright flash of light. Electronic circuits use large numbers of small capacitors. For example, a RAM (Random Access Memory) chip uses hundreds of thousands of very small capacitors coupled with switching transistors in a computer memory. Computer information is stored in a binary code of ones and zeros. A charged capacitor is a one, and an uncharged is a zero. These are just a few example of the many uses of capacitors.