Capacitor working principle

Capacitors are used to store charge so you can say that capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy. Inside the battery, chemical reactions produce electrons on one terminal and absorb electrons on the other terminal. A capacitor is much simpler than a battery, as it can't produce new electrons -- it only stores them.

Capacitor consist of two metal plates separated by a non-conducting substance, or dielectric. When DC voltage is applied across capacitor then +ve charge will get accumulated at one plate and –ve charge at another plate. +ve and –ve Charges are of equal amount.

A parallel plate capacitor consists of two conducting plates of same dimensions. These plates are
placed parallel to each other. Space between the plates is filled with air or any insulating material (dielectric). One plate is connected to positive terminal and other is connected to negative term-
inal of power supply. The plate connected to positive terminal acquires positive charge and the
other plate connected to negative terminal acquires equal negative charge .The charges are stored between the plates of capacitor due to attraction.

In theory, the dielectric can be any non-conductive substance. However, for practical applications, specific materials are used that best suit the capacitor's function. Mica, ceramic, cellulose, porcelain, Mylar, Teflon and even air are some of the non-conductive materials used. The dielectric dictates what kind of capacitor it is and for what it is best suited. Depending on the size and type of dielectric, some capacitors are better for high frequency uses, while some are better for high voltage applications.

Capacity of charge storage inside a capacitor. Here is your formula.
C=Q/V.

·         Air as dielectric medium are most  Often used in radio tuning circuits

·         Mylar- Most commonly used for timer circuits like clocks, alarms and counters

·         Glass- Good for high voltage applications

·         Ceramic - Used for high frequency purposes like antennas, X-ray and MRI machines

·         Super capacitor - Powers electric and hybrid cars

Capacitor storage capacity is measured in Farads. A 1-farad capacitor can store one coulomb  of charge at 1 volt. A coulomb is 6.25e18 (6.25 * 10^18, or 6.25 billion billion) electrons. One ampre presents a rate of electron flow of 1 coulomb of electrons per second, so a 1-farad capacitor can hold 1 amp-second of electrons at 1 volt.

A 1-farad capacitor would typically be pretty big. It might be as big as a can of tuna or a 1-liter soda bottle, depending on the voltage it can handle. For this reason, capacitors are typically measured in microfarads