Capacitor

When  we place two conducting surfaces  close to each other and separated by a dielectric or any insulating material between them then a capacitor /condenser is formed
                  OR
Any two conducting surfaces separated by a dielectric is called condensor or capacitor
Aluminium and tin are the most common conducting materials used in capacitor
Paper ,oil, ceramic,polyster etc are common insulataros
The two conductOr plates are usually kept parallel and the dielectric material keeps the conductor plates separated from each other
The capacitor functions as to store electrical charge and then releases it as when this energy is required
                WORKING
lets consider a capacitor
And connect it with a battery through key K
When we press the key the current flow through the circuit
The electrons from plate A will be attracted by the positive terminal of battery and these electrons start accumulating on plate B
Thus results more positive charge on plate A and more negative charge on plate B this is reffered as charging of capacitor this flow of charge remains continue till it acuries p.d to that of battery

 Factors on which capacitance depends
AREA OF PLATE:more the area of the plates of capacitor  larger is the capacitance of the capacitor and vice versa

THICKNESS OF DIELECTRIC MEDIUM;if there is smaller thinkness of dielectric between plates ,larger is the capacitance of capacitor or vice versa this is because capacitance of capacitor is inversely  propotional to the thinkness
           CAPACITANCE
capacitance is the ability of a capacitor to store charge .and is defined as the charge required to raise its potential through unity when a charge of Q coulombs is given to a conductor and if its potential raises from 0to v volts
According to expermental  observation it has been found that chargeQ stored in a capacitor is directly proportional to the potential difference across it
     Q directly proportional to V
     or    Q/V = constant =C
This constant C is called the  capacitance of the capacitor
Hence the capacitance of capacitor is defined as The ratio of charge  on capacitor plates to the p.d across the plate  is called capacitance
Units  of capacitance
 The SI unit of capacitance is farads
I,e
1farad=1C/1V
Hence  a capacitor is said to have a capacitance of 1 farad if a charge of 1C  accumulates on each plate against a p.d  of 1v across the plates

Following points should be noted;

1 No current can flow through the capacitor due to presence of dielectric between the plates of capacitors  which offers infinite resistance.the electric charge is mommentarily displaced from one plate to another plate through external circuits
2 as  p.d  between the plates is increased  ,the dielectric meadium comes under increasing stress.if p.d is increased,the stress in the dielectric increases till it can no longer bear it.At that stage, electrical breakdown  ocuures  which accompained by a spark between the two plates of capacitor. the maximum voltage per meter thickness which a meadium can withstand without a rupture or breakdown is called its dielectric  strength .usually it is given in Kv/mm instead  of the basic unit V/m.if two leads of a charged capacitor are connected together ,the p.d between the two plates is equalized and the capacitor becomes discharged.
3 since there exists a p.d between the two plates , an electric field is set up between them and whose strength is given by
E= V/d volt/meter