Introducing a dielectric into a capacitor decreases the electric field, which decreases the voltage, which increases the capacitance. A capacitor with a dielectric stores the same charge as one without a dielectric, but at a lower voltage. ... Voltage and capacitance are inversely proportional when charge is constant.

Why does a dielectric increase capacitance?

(a) The molecules in the insulating material between the plates of a capacitor are polarized by the charged plates. This produces a layer of opposite charge on the surface of the dielectric that attracts more charge onto the plate, increasing its capacitance.

What is effect of dielectric on capacitance?

The strength of the electric field is reduced due to the presence of dielectric. If the total charge on the plates is kept constant, then the potential difference is reduced across the capacitor plates. In this way, dielectric increases the capacitance of the capacitor.