CAPACITOR -  Capacitor is a system of two conductors separated by an insulator. The conductors have charges +Q and –Q and potential V₁  and V₂

                           Q  V

                            c = Q / V  , the constant c is called capacitance of the capacitor. Capacitance c depends only on the geometrical configuration (shape , size , separation of the two conductors .)

             S.I. unit of capacitance is ‘FARAD’ (F)

DEFINATION  OF 1 FARAD –

                           1F = 1 C/V

                           1µF = 10^-6 F                       &           1pF = 10^-12F

PARALLEL PLATE CAPACITOR -

The electric field in  outer region 1

  E = σ /2є₀ - σ /2є₀  = 0

The electric field outer region 2

                   E = σ /2є₀ - σ/2є₀  = 0

            Electric field in the inner region between the plates 1 and 2

             E = σ /2є₀ + σ /2є₀   = Q/ є₀A

              V = E . d = 1/ є₀ × Qd/ A

          The capacitance C on the parallel plate capacitor is

                          c = Q/V = є₀A/d

                           c = є₀A/d

         c depends on the factors

                         1-  c   A

                         2-  c   1/d