Chapter-2|Electrostatic Potential and Capacitance| NCERT 12th Physics:
Effect of Dielectric on Parallel Plate Capacitor:
Let a dielectric is inserted between the plates fully occupying the intervening reason. The dielectric is polarized by the electric field due to two metallic positive and negative plates.
Since, the direction of Eᵢ (Induced electric field) and E₀ (External electric field) are opposite in direction, then
From above it is clear that due to dielectric material the capacitance of the capacitor increases K times.