Physics - Capacitor Question with Solution | TestHub

When a dielectric material is introduced between the plates of a capacitor, it gets polarized due to the external electric field. This polarization creates an induced electric field inside the dielectric which opposes the external electric field.

As a result, the net electric field between the plates decreases. Since the potential difference is given by $V=E\times d$, the effective potential difference between the plates also decreases for a given charge.

This reduction in potential difference leads to an increase in the capacitance of the capacitor, as $C=\frac{Q}{V}$. Therefore, the function of a dielectric is to reduce the effective potential on the plates.