Question

Explain why the capacitance decrease when the dielectric medium is removed from between the plates.

Answer 1

When a dielectric medium is introduced between the plates of a parallel plate capacitor, the dielectric gets polarized by the electric field between the plates. As a result, the electric field and hence the potential difference between the plates of the capacitor decreases. Consequently, the capacitance of the capacitor increases since capacitance of a capacitor is inversely proportional to the potential difference between the plates of the capacitor, i.e.; $C=\frac{Q}{V}$.

The capacitance of a parallel plate capacitor with a dielectric slab of dielectric constant $K$ inserted in between the plates is given by,

$C=\frac{AK{ϵ}_0}{d}$

Where,

$A$ = Area of the plates

$d$ = separation between the plates

Now if the dielectric medium is removed from between the plates then the capacitance of the capacitor becomes, $C_0=\frac{A{ϵ}_0}{d}$.

Thus the capacitance of the capacitor decreases by a factor of $K$.