Capacitor is a device to store the charge and electricity. Dielectric are non conducting materials like wooden, Glass, etc.It is first discovered by Faraday that if the space between conductors of the capacitor is completely occupied by the dielectric then the capacitance of capacitor is increased by an factor K it is the characteristics of the dielectric and This factor is known as the dielectric constant. Dielectric constant of vacuum is unity.
C- capacitance of capacitor
Q -charge stored by capacitor
V- potential difference on capacitor
C- and V have opposite effect.
So if V decreases C increases.
For a good capacitor C should be high.
This can be possible by decreasing V.
V can be decrease by using dielectric between the capacitor plates.
If a material has polar molecules, they will be normally in random orientations when no electric field is applied. When we apply the electric field they will be polarized the material by orienting the dipole moments of polar molecules.
The presence of the dielectric decreases the electric field produced by a given charge density. Since the polarized particles also generate a electric field opposite to the main electric field. So effective electric field will be decrease by k.
The factor k by which the effective field is decreased by the polarization of the dielectric is called the dielectric constant of the material.
When a dielectric is placed between charged plates, the polarization of the medium produces an electric field opposing the field of the charges on the plate. The dielectric constant k is defined to effect the amount of reduction of effective electric field . The capacitance of the parallel plate conductor is increased by dielectric factor k.