When a dielectric is introduced between the plates of a capacitor, the capacity increases effectively. Explain.

A dielectric slab is introduced between the plates of a capacitor. Then the potential difference and the capacity respectively

What happens when a dielectric medium is introduced between the capacitor plates ?

A dielectric slab is introduced between the plates of a capacitor. Then the field intensity between the plates of the capacitor

The electric field intensity between the plates of a parallel plate capacitor decreases by 20%, when a dielectric slab is inserted between the plates. Find the dielectric constant of the dielectric.