What is a Capacitor?

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Capacitor is a passive component that has the ability to store the energy in the form potential difference between two plates. which form to be positive & negative depending upon the direction of charge storage. 

Symbol &Unit - The capacitor symbol is represented by drawing two parallel lines close to each other, but not touching. It consists of two terminals.

Standard units for capacitor is Farads. The most common subunits of capacitance are micro farad, nano farad (nF), pico farad (pF) & femo farad(fF) etc. 

1 micro farad = 10–⁶ farads
1 nano farad = 10–⁹ farads
1 pico farad = 10–¹² farads
1 femo farad = 10–¹⁵ farads

Construction of capacitor - A capacitor has the  ability to store electric energy in the form of electric field. A non conducting region is present between two plates which is called as dielectric material  (Insulator such as aluminum, paper,air,& ceramic etc).
When two plates having same area A, & distance between two parallel plate d,& if same energy is applied to the plates then the capacitance of the parallel plate capacitor can be termed as - 

Here are some relative permittivity values for a few substances -
Charging of capacitor - When the voltage V is applied across the capacitor plates, the electrons accumulate on the side of the capacitor connected to the negative terminal of the voltage source.The plate connected to the positive terminal of the voltage source loses electrons. This accumulation of electrons produces a negative charge. Thus, with the application of voltage, the electrons are simply redistributed from one side of the capacitor to the other. This redistribution process of the electrons is called charging of capacitor.
 The charging continues until the potential difference across the capacitor is equal to applied voltage.The more the applied voltage, the stronger is the electric field & more charge is stored in the dielectric.The 
amount of charge stored in the capacitor is, therefore, proportional to the applied voltage. 
Discharging of capacitor - When capacitor remains charged, then capacitor is connected to any electric device such as electric bulb through a conductive wire.
We know that electric current is the flow of charge carriers(free electrons). The electrons that started flowing from the right side plate through the conductive wire finally reach the left side plate & fill the holes of the left side plate.As the result, the charge on both plates start decreasing.Finally, the charge stored on the both plates of the capacitor discharged.As a result, the bulb will turn off, because no electric current flows through the bulb.

Connecting capacitors - A capacitor when connected in a circuit, that connected can be either series or parallel.
Capacitor in series- When n fixed  capacitors connected in series.The reciprocal of the capacitances of all capacitors is added to get the reciprocal of the total capacitance.

Capacitor in parallel- When capacitors are placed in parallel with one another the total capacitance is simply the sum of all capacitances.

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