Question

How does capactance with insertion of dielectric increases?

Answer 1

Parallel Plate with Dielectric. The capacitance of a set of charged parallel plates is increased by the insertion of a dielectric material. The capacitance is inversely proportional to the electric field between the plates, and the presence of the dielectric reduces the effective electric field.

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Answer 2

When a dielectric slab is introduced between the two plates of a parallel plate capacitor, the electric field is reduced and the capacitance of a capacitor is increased by K times.
i.e., Cm=KC0 where Cm is capacity of capacitor with dielectric medium introduced in it and C0= capacity of capacitor without dielectric and K is the dielectric constant