CBSE Class 12-science Answered

The generalised equation for the capacitance of a parallel plate capacitor is

C =εA/d

Where € is the permittivity of vacuum, A is the area of the plate and d is the distance between the plate.

In the above case, the medium between the two parallel plates is air.

The capacitance of capacitor can be changed by introducing a dielectric material that means by changing the (€)

If dielectric material is placed between the two parallel plates of capacitor then it's capacity of storing energy in the form of charge increases and it increases by a factor k( which is also known as dielectric constant)

The permittivity of dielectric is

ε(s)=ε(r) * ε(0)

Where, 

 ε(r) is the realtive permittivity,ε(s) is the permittivity of the medium, ε(0) is the permittivity of vaccumm.

Hence,

The capacitance of parallel plate capacitor filled with dielectric is C=ε(s)A/d

C=ε(r) * ε(0)*A/d

Now €(r) can be written as dielectric constant k

k =ε(r)= ε(s)/ε(0)

Hence C=kε(0)A/d