How Capacitors Work

Capacitors are like little batteries that store electrical energy, although they both function in completely different ways. Unlike a battery that produces electrons via the chemical reactions that occurs at one terminal and is absorbed on the other terminal. A capacitor can’t produce new electrons, it only stores them. Hence, a capacitor is simpler than a battery.



A capacitor stores electrons like a water tower; A water tower "stores" water pressure  when the water system pumps produce more water than a town needs, the excess is stored in the water tower. Then, at times of high demand, the excess water flows out of the tower to keep the pressure up.


The Capacitor consists of two metal plates placed in parallel, with a dielectric or non conducting substance isolating them from each other. So, there is no means of electric contact between them. A capacitor can be made using two pieces of aluminium foil and a piece of paper.


Suppose we have the circuit below:



Applying voltage to the plates generates an electric field between both plates which in turn causes a significant difference in the number of free electrons between them. Free electrons that are taken away from the positive connected plate are forced to gather on the negative connected plate. This is the representation of the charge effect of the capacitor. The greater number of electrons polarized, the greater field generated and the greater charge of the capacitor. When the capacitor is disconnected from the power supply, it will remain charged. An ideal capacitor would remain charged indefinitely. However, this is not possible in practice, owing to slight leakage current between both plates.


The dielectric determines what kind of capacitor it is and for what purpose it is best suited. Some Capacitors are best suited for high voltage applications while others work best when used in systems with high frequencies. Capacitors have many applications; they are used in calculator and in powering a commuter bus. NASA uses glass capacitors to help wake up the shuttle’s circuitry and assist in the deployment of space probes.